Dijkstra, Cor,

Dijkstra, Eelco,

Komdeur, Jan,

Dijkstra, Eelco

Komdeur, Jan

Dijkstra, Cor

ARTS repository - University of Groningen

   University of GroningenAdoption of young in the Blackbird Turdus merulaDijkstra, Eelco; Komdeur, Jan; Dijkstra, CorPublished in:IbisIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1997Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Dijkstra, E., Komdeur, J., & Dijkstra, C. (1997). Adoption of young in the Blackbird Turdus merula. Ibis,139(1), 174-175.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 16-07-20231 7 4  S H O R T  C O M  M I J N  I C A ' r I  ( I N S  I R I S  1 3 9  Egg Total Nestling Total predation predation predation by voles by voles predation Hatched nestling Vole Total Un- nest- Total egg predation (No. found eggs lings dcnsity eggs hatched by voles Year pcr h a )  I )  n n ' X ,  n '%, n II '%, I 1  '%I I 1  '%, 1993 40 132 10 22 17 18 14 100 16 16 12 12 30 22.7 7994 1 5  1 3 3  9 27 20 1 3  10 97 18 19 9 9 22 16.5 1 W i  4 134 6 11 8 7 5 117 20 17 5 4 12 9.0 I+edatio~i by voles detected by a video camera and by other signs as described in the text. cad i  (trodden by Chamois Hirpicnpm nrpicapm and bitten by Carabid bcctlcs) were placed 30-100 cm from vole burrows. The nestlings wc'rc 3 davs and 7 days old and weighed 3.559 g. A video camera w.ts locused on the nest (in one instance a 500-mm lens was used to photograph from a hide). 'I'he study was carried out in June 1 OY 5. In each ciise the C'ominon Voles took both the eggs and the nest- Iiiigs into their burrows. 'I'he nestlings were bitten on the head and immediately pulled into the burrows. None of the nests were dis- turbed by the voles. The removal of the prey from these nests which Mere less well concealed than natural nests. into burrows was prob- ably inlluenced by the vole's antipredator behaviour. In addition, pieces of eggshells. egg contents soaked into the nest and vole drop- pings were found in about half of the natural pipit nests. which werc mainly well hidden. examined. Partially devoured nestlings wcre sporadically found in nests. and they were sometimes fouiid i i i  the grass near the nests. Parts of their bodies. often the head and legs. were partly devoured. In most cases. the nestlings had been Idled by a bite through the skull. l'he predation on Meadow Pipit eggs and nestlings changed with the density of' the voles during their cycle of numbers. The voles wcrc the most important predators during the vole outbreak (Table 1 ). The approximate spring density of voles was estimated from the iiumber of observed occupied burrows found on a strip transect I 300 X L m). Verbeek (1970) recorded similar signs of Deer Mouse predation on Water Pipit eggs and nestlings. Again. the predation oii cggs was much higher when the Deer Mice were plentiful. I'he results confirm the suggestion of Piatt et ( 1 1 .  (1990) that the disappearance of eggs and nestlings could have been caused by WJICS. I3ased on the results above. egg and nestling predation by voles could be usual throughout their range. REFERENCES Furness. R.W. 1988. Predation of ground-nesting seabirds by is- land populations of red deer Cerims elnplius and sheep Ovis. J. Zool. Lond. 216: 565-573. Major. R.E. 199 1. Identification of nest predators by photography. dummy eggs. and adhesive tape. Auk 108: 190-195. Maxson. S.J. & Oring, L.W. 1978. Mice as a source 0 1  egg loss among ground-nesting birds. Auk 95: 582-584. Murray. K.G..  Winnet-Murray. K.. Eppley. Z.A.. Hunt. C.L. & Schwartz, D.B. 1Y83. Breeding biology ul' the Xantus' Murrelet. Condor 8 5: 12-2 1. Niethammer. J. & Krapp. F. (cds). 1978. Handbuch der Saugetiere Europas. Band I-Rodentia 1 .  Wiesbadcn: Academische Verlags- gesellshaft Wiesbaden. Obrtel. R.  81 HoliSova. V 1977. Sufficient sample sixe for analyses of small rodent diets. Folia Zool. 26: 193-205. Pedroli. J.C. 1978. Breeding success of the Meadow Pipit Aritluis prciteiisis in the Swiss Jura. Ornis Scand. 9: 168-171. Pennington. M.G. 1992. Predation of birds' cggs and chicks by herbivorous mammals. Scot. Birds 16: 285. Pialt. J.E. Roberts. B.11.. Lidster. W.W.. Wells. J.L. & Hatch. S.A. 1990. Effect of human disturbance on breeding Least and Crest- ed Auldets at St. Lawrence Island. Alaska. iiulr 107: 342- 3 50. Sealy. S.G. 1982. Voles as a source of egg and nestling loss among nesting auklets. Murrelet 63:  9-14. Verbeek, N.A.M. 1970. Breeding biology 0 1  the Water Pipit. Auk 87: 425-451. Adoption of young in the Blackbird Turdus merula The term "adoption" is defined as the provision of care to young by unrelated adults. Of the bird species studied with biparerital care. adoptive behaviour has been recorded in 17 species. and only by replacement males (Meek & Robertson 1991). Rohwer's (1986) hy- pothesis is that adoption may facilitate the replacement male ac- quiring the female for renesting (either within or between breeding seasons). It is expected that adoption will be favoured within brccd- ing seasons in double-brooded species that break the pair bond and disperse following nest failure but maintain pair bonds following 1 9 9 7  S H 0 R 1 C 0 M M U N I C A T  10 N S 1 7 5  successful nesting. Only nine studies have quantified the amount of care provided when replacement males feed young. and there are 110 documented examples of full adoption by a replacement breed- ing pair (Meek & Kobertson 1991). We record a rare case of adop- tion of young by a breeding pair in the Blackbird Turdus merulu. ohscrvcd in The Netherlands. Blackbirds are territorial. sexually dimorphic birds. Observations on thc breeding ecology of colour-ringed birds showed that only the femtrle incubate. but both parents feed the nestlings until they fledge 13-14 days after hatching (Snow 1958.  Reise 1990,  Magrath 1992, Schnack 1991) .  In the Netherlands. clutches are usually laid lroni mid-March to late June. during which time a pair can raise twtr broods. sometimes more (Snow 1958.  Glutz & Bauer 1988) .  Advptions in the Blackbird have not been reported previously (Reise 1990. Magrath 1992.  Meek & Robertson 1991. Schnack 1991) .  In May 1995 a breeding pair (male 1 and female 1 )  built a nest at ii height of 4 m in a spruce tree, 3 m from a window. which offered good opportunities for observation. Soon after the female started incubating. the male was injured by a cat. Due to damaged flight leathers in one wing and the loss of all tail feathers he was unahle to fly and after 7 week he was found dead. The female, which was also identifiable by the absence of tail feathers. remained incubating. During the first 2 days alter hatching, the female stayed on the nest lor 80% of the day and fed the young infrequently (mean feedings per hour i s.e.=0.51 2 0.05; the iiest was ob- served for N hi. Two days after hatching. another pair (male 2 and female 2) .  with undamaged plumage and therefore distinguishable from pair 1. entered the territory. When the male approached the nest. female 1 immediately flew ofr and did not defend her nestlings. However. after a brief inspection. the male started foraging and soon afterward returned to the nest with food and fed the young. During the nestling phase. he took a i0'% share of all feedings (mean feeding rate per hour, female 1 = 1.62 i 0.20: male 2 = 1.86 i 0.16; ti = h h) .  Female 1 did not show any aggressive behaviour toward male 2 or female 2. Instead, she avoided them, leaving the nest immcdiately when one of the others landed in the nest tree. but shc continued feeding her young. Female 2 did not show overt aggression toward female 7 or the young, but she fol- lowed her persistently wherever she went. Two days after the arrival of pair 2. female 2 started building her own nest 1 m above the nest built by pair 1. The male did not assist her hut only fed the young in the first nest. Female 2 laid eggs, hut her clutch was lost c. 3 (lays after she started incubation. After the clutch loss. she also adopted the young in nest 1 by feeding thcrn, though the feeding rate was low (mean feeding rate per hour = 0.32 i 0.11: II = 8 h). At least oiie nestling fledged and was k d  by male 2 away from the nest. The interpretation of the observed adoption behaviour remains speculalivc. as the degree of genetic relatedness between these in- dividuals is unknown. Obviously for female 1. receiving help at the nest IS advantageous for offspring survival. Without this help she would probably have lost her entire brood. since she would not have been able to hoth brood and feed the newly hatched young properly. Adoption by the new inale would he adaptive from his point of view when he had fathered (some of] the young by extra-pair fertilixa- tion. If the ncw male was related to female 1. his adoptive behav- iour t~ould he explained in terms of gaining indirect fitness benefits through the production of related young (Emlen 1995). I f  unrc- lated to female 1. he would gain no clear titness benefits. unless adoption served as a way of establishing a new pair bond with a high-quality partner. For female 2. adoption was not associated with obtaining breeding status: she adopted the young of female 1 after failure of her own clutch. Again. this could he adaptive for her if she was related to female 1. However. being a breeder is generally the most productive. and one might wonder why female 2 did not destroy the brood of female 1 (who seemed to be sub- missive) and expel her from the territory. By this action she might have gained better brood care from her partner, resulting in sur- viving offspring of her own. We are grateful for comments by Ben Hatchwell (Shellield Univer- sity. IJK) and Joost Tinbergen (Groningen Ilniversity. The Nether- lands). REFERENCES Emlen. S.?: 1995.  An evolutionary theory of the family. Proc. Natl. Acad. Sci. U.S.A. 92: 8092-8099. Glutz. I1.N. h; Bauer, K.M. 1988. Handbuch der Vbgel Mitteleuro- pas 11 /It. Wiesbaden: "LA-Verlag. Magrath, R.D. 1992. Seasonal changes in egg-mass within and among clutches of birds: General explanations and a field study of the Blackbird T~rrdus rnerula. Ibis 134: 171-179. Meek, S.B. & Robertson. K.J. 1991.  Adoption of young by replace- ment male birds: An experimental study of eastern bluebirds and a review. Anim. Behav. 42: 81 3-820. Kcise, H. 1990. Observations on ecology and biology of the Hlack- bird (Turdus tnerula) in the Leipxig City (Poland). Zoologische Ab- handlungen (Dresden) 45(9-19): 155-1 78. Rohwer. S. 1986.  Selection for adoption versus infanticide by re- placement 'mates' in birds. Current Ornith. 3 :  353-395. Schnack. S. 1991.  The breeding hiology arid nestling diet of the Blackbird Turdus rrierula 1,. and the Song Thrush Turdus pliilorlir- IIOS C.L. Brelini in Vienna and in a n  adjacent wood. Acta Orn. Warsz. 26(2): 85-106. Snow, D.W. 1958.  A Study of Blackbirds. London: Allen K. Uiiwin. Srrbrriittrrl 2 0  kbrurwy 1996; rrvisiori accepted 20 ilflarrli 1996 Habitat selection by marine birds in relation to water depth A recent analysis of seabird abundance in relation to water depth (Stone et crl. 1995)  showed that some species (auks and Manx Shearwaters Puffirius prffinirs) were restricted largely to continental shelf waters less than 1 0 0  m in depth. while other species (Fulmars 

English

Adoption of young in the Blackbird <i>Turdus merula</i>

Proceedings - University of Groningen

   University of GroningenAdoption of young in the Blackbird Turdus merulaDijkstra, Eelco; Komdeur, Jan; Dijkstra, CorPublished in:IbisIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1997Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Dijkstra, E., Komdeur, J., & Dijkstra, C. (1997). Adoption of young in the Blackbird Turdus merula. Ibis,139(1), 174-175.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 09-09-20231 7 4  S H O R T  C O M  M I J N  I C A ' r I  ( I N S  I R I S  1 3 9  Egg Total Nestling Total predation predation predation by voles by voles predation Hatched nestling Vole Total Un- nest- Total egg predation (No. found eggs lings dcnsity eggs hatched by voles Year pcr h a )  I )  n n ' X ,  n '%, n II '%, I 1  '%I I 1  '%, 1993 40 132 10 22 17 18 14 100 16 16 12 12 30 22.7 7994 1 5  1 3 3  9 27 20 1 3  10 97 18 19 9 9 22 16.5 1 W i  4 134 6 11 8 7 5 117 20 17 5 4 12 9.0 I+edatio~i by voles detected by a video camera and by other signs as described in the text. cad i  (trodden by Chamois Hirpicnpm nrpicapm and bitten by Carabid bcctlcs) were placed 30-100 cm from vole burrows. The nestlings wc'rc 3 davs and 7 days old and weighed 3.559 g. A video camera w.ts locused on the nest (in one instance a 500-mm lens was used to photograph from a hide). 'I'he study was carried out in June 1 OY 5. In each ciise the C'ominon Voles took both the eggs and the nest- Iiiigs into their burrows. 'I'he nestlings were bitten on the head and immediately pulled into the burrows. None of the nests were dis- turbed by the voles. The removal of the prey from these nests which Mere less well concealed than natural nests. into burrows was prob- ably inlluenced by the vole's antipredator behaviour. In addition, pieces of eggshells. egg contents soaked into the nest and vole drop- pings were found in about half of the natural pipit nests. which werc mainly well hidden. examined. Partially devoured nestlings wcre sporadically found in nests. and they were sometimes fouiid i i i  the grass near the nests. Parts of their bodies. often the head and legs. were partly devoured. In most cases. the nestlings had been Idled by a bite through the skull. l'he predation on Meadow Pipit eggs and nestlings changed with the density of' the voles during their cycle of numbers. The voles wcrc the most important predators during the vole outbreak (Table 1 ). The approximate spring density of voles was estimated from the iiumber of observed occupied burrows found on a strip transect I 300 X L m). Verbeek (1970) recorded similar signs of Deer Mouse predation on Water Pipit eggs and nestlings. Again. the predation oii cggs was much higher when the Deer Mice were plentiful. I'he results confirm the suggestion of Piatt et ( 1 1 .  (1990) that the disappearance of eggs and nestlings could have been caused by WJICS. I3ased on the results above. egg and nestling predation by voles could be usual throughout their range. REFERENCES Furness. R.W. 1988. Predation of ground-nesting seabirds by is- land populations of red deer Cerims elnplius and sheep Ovis. J. Zool. Lond. 216: 565-573. Major. R.E. 199 1. Identification of nest predators by photography. dummy eggs. and adhesive tape. Auk 108: 190-195. Maxson. S.J. & Oring, L.W. 1978. Mice as a source 0 1  egg loss among ground-nesting birds. Auk 95: 582-584. Murray. K.G..  Winnet-Murray. K.. Eppley. Z.A.. Hunt. C.L. & Schwartz, D.B. 1Y83. Breeding biology ul' the Xantus' Murrelet. Condor 8 5: 12-2 1. Niethammer. J. & Krapp. F. (cds). 1978. Handbuch der Saugetiere Europas. Band I-Rodentia 1 .  Wiesbadcn: Academische Verlags- gesellshaft Wiesbaden. Obrtel. R.  81 HoliSova. V 1977. Sufficient sample sixe for analyses of small rodent diets. Folia Zool. 26: 193-205. Pedroli. J.C. 1978. Breeding success of the Meadow Pipit Aritluis prciteiisis in the Swiss Jura. Ornis Scand. 9: 168-171. Pennington. M.G. 1992. Predation of birds' cggs and chicks by herbivorous mammals. Scot. Birds 16: 285. Pialt. J.E. Roberts. B.11.. Lidster. W.W.. Wells. J.L. & Hatch. S.A. 1990. Effect of human disturbance on breeding Least and Crest- ed Auldets at St. Lawrence Island. Alaska. iiulr 107: 342- 3 50. Sealy. S.G. 1982. Voles as a source of egg and nestling loss among nesting auklets. Murrelet 63:  9-14. Verbeek, N.A.M. 1970. Breeding biology 0 1  the Water Pipit. Auk 87: 425-451. Adoption of young in the Blackbird Turdus merula The term "adoption" is defined as the provision of care to young by unrelated adults. Of the bird species studied with biparerital care. adoptive behaviour has been recorded in 17 species. and only by replacement males (Meek & Robertson 1991). Rohwer's (1986) hy- pothesis is that adoption may facilitate the replacement male ac- quiring the female for renesting (either within or between breeding seasons). It is expected that adoption will be favoured within brccd- ing seasons in double-brooded species that break the pair bond and disperse following nest failure but maintain pair bonds following 1 9 9 7  S H 0 R 1 C 0 M M U N I C A T  10 N S 1 7 5  successful nesting. Only nine studies have quantified the amount of care provided when replacement males feed young. and there are 110 documented examples of full adoption by a replacement breed- ing pair (Meek & Kobertson 1991). We record a rare case of adop- tion of young by a breeding pair in the Blackbird Turdus merulu. ohscrvcd in The Netherlands. Blackbirds are territorial. sexually dimorphic birds. Observations on thc breeding ecology of colour-ringed birds showed that only the femtrle incubate. but both parents feed the nestlings until they fledge 13-14 days after hatching (Snow 1958.  Reise 1990,  Magrath 1992, Schnack 1991) .  In the Netherlands. clutches are usually laid lroni mid-March to late June. during which time a pair can raise twtr broods. sometimes more (Snow 1958.  Glutz & Bauer 1988) .  Advptions in the Blackbird have not been reported previously (Reise 1990. Magrath 1992.  Meek & Robertson 1991. Schnack 1991) .  In May 1995 a breeding pair (male 1 and female 1 )  built a nest at ii height of 4 m in a spruce tree, 3 m from a window. which offered good opportunities for observation. Soon after the female started incubating. the male was injured by a cat. Due to damaged flight leathers in one wing and the loss of all tail feathers he was unahle to fly and after 7 week he was found dead. The female, which was also identifiable by the absence of tail feathers. remained incubating. During the first 2 days alter hatching, the female stayed on the nest lor 80% of the day and fed the young infrequently (mean feedings per hour i s.e.=0.51 2 0.05; the iiest was ob- served for N hi. Two days after hatching. another pair (male 2 and female 2) .  with undamaged plumage and therefore distinguishable from pair 1. entered the territory. When the male approached the nest. female 1 immediately flew ofr and did not defend her nestlings. However. after a brief inspection. the male started foraging and soon afterward returned to the nest with food and fed the young. During the nestling phase. he took a i0'% share of all feedings (mean feeding rate per hour, female 1 = 1.62 i 0.20: male 2 = 1.86 i 0.16; ti = h h) .  Female 1 did not show any aggressive behaviour toward male 2 or female 2. Instead, she avoided them, leaving the nest immcdiately when one of the others landed in the nest tree. but shc continued feeding her young. Female 2 did not show overt aggression toward female 7 or the young, but she fol- lowed her persistently wherever she went. Two days after the arrival of pair 2. female 2 started building her own nest 1 m above the nest built by pair 1. The male did not assist her hut only fed the young in the first nest. Female 2 laid eggs, hut her clutch was lost c. 3 (lays after she started incubation. After the clutch loss. she also adopted the young in nest 1 by feeding thcrn, though the feeding rate was low (mean feeding rate per hour = 0.32 i 0.11: II = 8 h). At least oiie nestling fledged and was k d  by male 2 away from the nest. The interpretation of the observed adoption behaviour remains speculalivc. as the degree of genetic relatedness between these in- dividuals is unknown. Obviously for female 1. receiving help at the nest IS advantageous for offspring survival. Without this help she would probably have lost her entire brood. since she would not have been able to hoth brood and feed the newly hatched young properly. Adoption by the new inale would he adaptive from his point of view when he had fathered (some of] the young by extra-pair fertilixa- tion. If the ncw male was related to female 1. his adoptive behav- iour t~ould he explained in terms of gaining indirect fitness benefits through the production of related young (Emlen 1995). I f  unrc- lated to female 1. he would gain no clear titness benefits. unless adoption served as a way of establishing a new pair bond with a high-quality partner. For female 2. adoption was not associated with obtaining breeding status: she adopted the young of female 1 after failure of her own clutch. Again. this could he adaptive for her if she was related to female 1. However. being a breeder is generally the most productive. and one might wonder why female 2 did not destroy the brood of female 1 (who seemed to be sub- missive) and expel her from the territory. By this action she might have gained better brood care from her partner, resulting in sur- viving offspring of her own. We are grateful for comments by Ben Hatchwell (Shellield Univer- sity. IJK) and Joost Tinbergen (Groningen Ilniversity. The Nether- lands). REFERENCES Emlen. S.?: 1995.  An evolutionary theory of the family. Proc. Natl. Acad. Sci. U.S.A. 92: 8092-8099. Glutz. I1.N. h; Bauer, K.M. 1988. Handbuch der Vbgel Mitteleuro- pas 11 /It. Wiesbaden: "LA-Verlag. Magrath, R.D. 1992. Seasonal changes in egg-mass within and among clutches of birds: General explanations and a field study of the Blackbird T~rrdus rnerula. Ibis 134: 171-179. Meek, S.B. & Robertson. K.J. 1991.  Adoption of young by replace- ment male birds: An experimental study of eastern bluebirds and a review. Anim. Behav. 42: 81 3-820. Kcise, H. 1990. Observations on ecology and biology of the Hlack- bird (Turdus tnerula) in the Leipxig City (Poland). Zoologische Ab- handlungen (Dresden) 45(9-19): 155-1 78. Rohwer. S. 1986.  Selection for adoption versus infanticide by re- placement 'mates' in birds. Current Ornith. 3 :  353-395. Schnack. S. 1991.  The breeding hiology arid nestling diet of the Blackbird Turdus rrierula 1,. and the Song Thrush Turdus pliilorlir- IIOS C.L. Brelini in Vienna and in a n  adjacent wood. Acta Orn. Warsz. 26(2): 85-106. Snow, D.W. 1958.  A Study of Blackbirds. London: Allen K. Uiiwin. Srrbrriittrrl 2 0  kbrurwy 1996; rrvisiori accepted 20 ilflarrli 1996 Habitat selection by marine birds in relation to water depth A recent analysis of seabird abundance in relation to water depth (Stone et crl. 1995)  showed that some species (auks and Manx Shearwaters Puffirius prffinirs) were restricted largely to continental shelf waters less than 1 0 0  m in depth. while other species (Fulmars 

University of Groningen

   University of GroningenAdoption of young in the Blackbird Turdus merulaDijkstra, Eelco; Komdeur, Jan; Dijkstra, CorPublished in:IbisIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1997Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Dijkstra, E., Komdeur, J., & Dijkstra, C. (1997). Adoption of young in the Blackbird Turdus merula. Ibis,139(1), 174-175.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 12-11-20191 7 4  S H O R T  C O M  M I J N  I C A ' r I  ( I N S  I R I S  1 3 9  Egg Total Nestling Total predation predation predation by voles by voles predation Hatched nestling Vole Total Un- nest- Total egg predation (No. found eggs lings dcnsity eggs hatched by voles Year pcr h a )  I )  n n ' X ,  n '%, n II '%, I 1  '%I I 1  '%, 1993 40 132 10 22 17 18 14 100 16 16 12 12 30 22.7 7994 1 5  1 3 3  9 27 20 1 3  10 97 18 19 9 9 22 16.5 1 W i  4 134 6 11 8 7 5 117 20 17 5 4 12 9.0 I+edatio~i by voles detected by a video camera and by other signs as described in the text. cad i  (trodden by Chamois Hirpicnpm nrpicapm and bitten by Carabid bcctlcs) were placed 30-100 cm from vole burrows. The nestlings wc'rc 3 davs and 7 days old and weighed 3.559 g. A video camera w.ts locused on the nest (in one instance a 500-mm lens was used to photograph from a hide). 'I'he study was carried out in June 1 OY 5. In each ciise the C'ominon Voles took both the eggs and the nest- Iiiigs into their burrows. 'I'he nestlings were bitten on the head and immediately pulled into the burrows. None of the nests were dis- turbed by the voles. The removal of the prey from these nests which Mere less well concealed than natural nests. into burrows was prob- ably inlluenced by the vole's antipredator behaviour. In addition, pieces of eggshells. egg contents soaked into the nest and vole drop- pings were found in about half of the natural pipit nests. which werc mainly well hidden. examined. Partially devoured nestlings wcre sporadically found in nests. and they were sometimes fouiid i i i  the grass near the nests. Parts of their bodies. often the head and legs. were partly devoured. In most cases. the nestlings had been Idled by a bite through the skull. l'he predation on Meadow Pipit eggs and nestlings changed with the density of' the voles during their cycle of numbers. The voles wcrc the most important predators during the vole outbreak (Table 1 ). The approximate spring density of voles was estimated from the iiumber of observed occupied burrows found on a strip transect I 300 X L m). Verbeek (1970) recorded similar signs of Deer Mouse predation on Water Pipit eggs and nestlings. Again. the predation oii cggs was much higher when the Deer Mice were plentiful. I'he results confirm the suggestion of Piatt et ( 1 1 .  (1990) that the disappearance of eggs and nestlings could have been caused by WJICS. I3ased on the results above. egg and nestling predation by voles could be usual throughout their range. REFERENCES Furness. R.W. 1988. Predation of ground-nesting seabirds by is- land populations of red deer Cerims elnplius and sheep Ovis. J. Zool. Lond. 216: 565-573. Major. R.E. 199 1. Identification of nest predators by photography. dummy eggs. and adhesive tape. Auk 108: 190-195. Maxson. S.J. & Oring, L.W. 1978. Mice as a source 0 1  egg loss among ground-nesting birds. Auk 95: 582-584. Murray. K.G..  Winnet-Murray. K.. Eppley. Z.A.. Hunt. C.L. & Schwartz, D.B. 1Y83. Breeding biology ul' the Xantus' Murrelet. Condor 8 5: 12-2 1. Niethammer. J. & Krapp. F. (cds). 1978. Handbuch der Saugetiere Europas. Band I-Rodentia 1 .  Wiesbadcn: Academische Verlags- gesellshaft Wiesbaden. Obrtel. R.  81 HoliSova. V 1977. Sufficient sample sixe for analyses of small rodent diets. Folia Zool. 26: 193-205. Pedroli. J.C. 1978. Breeding success of the Meadow Pipit Aritluis prciteiisis in the Swiss Jura. Ornis Scand. 9: 168-171. Pennington. M.G. 1992. Predation of birds' cggs and chicks by herbivorous mammals. Scot. Birds 16: 285. Pialt. J.E. Roberts. B.11.. Lidster. W.W.. Wells. J.L. & Hatch. S.A. 1990. Effect of human disturbance on breeding Least and Crest- ed Auldets at St. Lawrence Island. Alaska. iiulr 107: 342- 3 50. Sealy. S.G. 1982. Voles as a source of egg and nestling loss among nesting auklets. Murrelet 63:  9-14. Verbeek, N.A.M. 1970. Breeding biology 0 1  the Water Pipit. Auk 87: 425-451. Adoption of young in the Blackbird Turdus merula The term "adoption" is defined as the provision of care to young by unrelated adults. Of the bird species studied with biparerital care. adoptive behaviour has been recorded in 17 species. and only by replacement males (Meek & Robertson 1991). Rohwer's (1986) hy- pothesis is that adoption may facilitate the replacement male ac- quiring the female for renesting (either within or between breeding seasons). It is expected that adoption will be favoured within brccd- ing seasons in double-brooded species that break the pair bond and disperse following nest failure but maintain pair bonds following 1 9 9 7  S H 0 R 1 C 0 M M U N I C A T  10 N S 1 7 5  successful nesting. Only nine studies have quantified the amount of care provided when replacement males feed young. and there are 110 documented examples of full adoption by a replacement breed- ing pair (Meek & Kobertson 1991). We record a rare case of adop- tion of young by a breeding pair in the Blackbird Turdus merulu. ohscrvcd in The Netherlands. Blackbirds are territorial. sexually dimorphic birds. Observations on thc breeding ecology of colour-ringed birds showed that only the femtrle incubate. but both parents feed the nestlings until they fledge 13-14 days after hatching (Snow 1958.  Reise 1990,  Magrath 1992, Schnack 1991) .  In the Netherlands. clutches are usually laid lroni mid-March to late June. during which time a pair can raise twtr broods. sometimes more (Snow 1958.  Glutz & Bauer 1988) .  Advptions in the Blackbird have not been reported previously (Reise 1990. Magrath 1992.  Meek & Robertson 1991. Schnack 1991) .  In May 1995 a breeding pair (male 1 and female 1 )  built a nest at ii height of 4 m in a spruce tree, 3 m from a window. which offered good opportunities for observation. Soon after the female started incubating. the male was injured by a cat. Due to damaged flight leathers in one wing and the loss of all tail feathers he was unahle to fly and after 7 week he was found dead. The female, which was also identifiable by the absence of tail feathers. remained incubating. During the first 2 days alter hatching, the female stayed on the nest lor 80% of the day and fed the young infrequently (mean feedings per hour i s.e.=0.51 2 0.05; the iiest was ob- served for N hi. Two days after hatching. another pair (male 2 and female 2) .  with undamaged plumage and therefore distinguishable from pair 1. entered the territory. When the male approached the nest. female 1 immediately flew ofr and did not defend her nestlings. However. after a brief inspection. the male started foraging and soon afterward returned to the nest with food and fed the young. During the nestling phase. he took a i0'% share of all feedings (mean feeding rate per hour, female 1 = 1.62 i 0.20: male 2 = 1.86 i 0.16; ti = h h) .  Female 1 did not show any aggressive behaviour toward male 2 or female 2. Instead, she avoided them, leaving the nest immcdiately when one of the others landed in the nest tree. but shc continued feeding her young. Female 2 did not show overt aggression toward female 7 or the young, but she fol- lowed her persistently wherever she went. Two days after the arrival of pair 2. female 2 started building her own nest 1 m above the nest built by pair 1. The male did not assist her hut only fed the young in the first nest. Female 2 laid eggs, hut her clutch was lost c. 3 (lays after she started incubation. After the clutch loss. she also adopted the young in nest 1 by feeding thcrn, though the feeding rate was low (mean feeding rate per hour = 0.32 i 0.11: II = 8 h). At least oiie nestling fledged and was k d  by male 2 away from the nest. The interpretation of the observed adoption behaviour remains speculalivc. as the degree of genetic relatedness between these in- dividuals is unknown. Obviously for female 1. receiving help at the nest IS advantageous for offspring survival. Without this help she would probably have lost her entire brood. since she would not have been able to hoth brood and feed the newly hatched young properly. Adoption by the new inale would he adaptive from his point of view when he had fathered (some of] the young by extra-pair fertilixa- tion. If the ncw male was related to female 1. his adoptive behav- iour t~ould he explained in terms of gaining indirect fitness benefits through the production of related young (Emlen 1995). I f  unrc- lated to female 1. he would gain no clear titness benefits. unless adoption served as a way of establishing a new pair bond with a high-quality partner. For female 2. adoption was not associated with obtaining breeding status: she adopted the young of female 1 after failure of her own clutch. Again. this could he adaptive for her if she was related to female 1. However. being a breeder is generally the most productive. and one might wonder why female 2 did not destroy the brood of female 1 (who seemed to be sub- missive) and expel her from the territory. By this action she might have gained better brood care from her partner, resulting in sur- viving offspring of her own. We are grateful for comments by Ben Hatchwell (Shellield Univer- sity. IJK) and Joost Tinbergen (Groningen Ilniversity. The Nether- lands). REFERENCES Emlen. S.?: 1995.  An evolutionary theory of the family. Proc. Natl. Acad. Sci. U.S.A. 92: 8092-8099. Glutz. I1.N. h; Bauer, K.M. 1988. Handbuch der Vbgel Mitteleuro- pas 11 /It. Wiesbaden: "LA-Verlag. Magrath, R.D. 1992. Seasonal changes in egg-mass within and among clutches of birds: General explanations and a field study of the Blackbird T~rrdus rnerula. Ibis 134: 171-179. Meek, S.B. & Robertson. K.J. 1991.  Adoption of young by replace- ment male birds: An experimental study of eastern bluebirds and a review. Anim. Behav. 42: 81 3-820. Kcise, H. 1990. Observations on ecology and biology of the Hlack- bird (Turdus tnerula) in the Leipxig City (Poland). Zoologische Ab- handlungen (Dresden) 45(9-19): 155-1 78. Rohwer. S. 1986.  Selection for adoption versus infanticide by re- placement 'mates' in birds. Current Ornith. 3 :  353-395. Schnack. S. 1991.  The breeding hiology arid nestling diet of the Blackbird Turdus rrierula 1,. and the Song Thrush Turdus pliilorlir- IIOS C.L. Brelini in Vienna and in a n  adjacent wood. Acta Orn. Warsz. 26(2): 85-106. Snow, D.W. 1958.  A Study of Blackbirds. London: Allen K. Uiiwin. Srrbrriittrrl 2 0  kbrurwy 1996; rrvisiori accepted 20 ilflarrli 1996 Habitat selection by marine birds in relation to water depth A recent analysis of seabird abundance in relation to water depth (Stone et crl. 1995)  showed that some species (auks and Manx Shearwaters Puffirius prffinirs) were restricted largely to continental shelf waters less than 1 0 0  m in depth. while other species (Fulmars 

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Adoption of young in the Blackbird Turdus merula

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   University of GroningenAdoption of young in the Blackbird Turdus merulaDijkstra, Eelco; Komdeur, Jan; Dijkstra, CorPublished in:IbisIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1997Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Dijkstra, E., Komdeur, J., & Dijkstra, C. (1997). Adoption of young in the Blackbird Turdus merula. Ibis,139(1), 174-175.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 03-06-20221 7 4  S H O R T  C O M  M I J N  I C A ' r I  ( I N S  I R I S  1 3 9  Egg Total Nestling Total predation predation predation by voles by voles predation Hatched nestling Vole Total Un- nest- Total egg predation (No. found eggs lings dcnsity eggs hatched by voles Year pcr h a )  I )  n n ' X ,  n '%, n II '%, I 1  '%I I 1  '%, 1993 40 132 10 22 17 18 14 100 16 16 12 12 30 22.7 7994 1 5  1 3 3  9 27 20 1 3  10 97 18 19 9 9 22 16.5 1 W i  4 134 6 11 8 7 5 117 20 17 5 4 12 9.0 I+edatio~i by voles detected by a video camera and by other signs as described in the text. cad i  (trodden by Chamois Hirpicnpm nrpicapm and bitten by Carabid bcctlcs) were placed 30-100 cm from vole burrows. The nestlings wc'rc 3 davs and 7 days old and weighed 3.559 g. A video camera w.ts locused on the nest (in one instance a 500-mm lens was used to photograph from a hide). 'I'he study was carried out in June 1 OY 5. In each ciise the C'ominon Voles took both the eggs and the nest- Iiiigs into their burrows. 'I'he nestlings were bitten on the head and immediately pulled into the burrows. None of the nests were dis- turbed by the voles. The removal of the prey from these nests which Mere less well concealed than natural nests. into burrows was prob- ably inlluenced by the vole's antipredator behaviour. In addition, pieces of eggshells. egg contents soaked into the nest and vole drop- pings were found in about half of the natural pipit nests. which werc mainly well hidden. examined. Partially devoured nestlings wcre sporadically found in nests. and they were sometimes fouiid i i i  the grass near the nests. Parts of their bodies. often the head and legs. were partly devoured. In most cases. the nestlings had been Idled by a bite through the skull. l'he predation on Meadow Pipit eggs and nestlings changed with the density of' the voles during their cycle of numbers. The voles wcrc the most important predators during the vole outbreak (Table 1 ). The approximate spring density of voles was estimated from the iiumber of observed occupied burrows found on a strip transect I 300 X L m). Verbeek (1970) recorded similar signs of Deer Mouse predation on Water Pipit eggs and nestlings. Again. the predation oii cggs was much higher when the Deer Mice were plentiful. I'he results confirm the suggestion of Piatt et ( 1 1 .  (1990) that the disappearance of eggs and nestlings could have been caused by WJICS. I3ased on the results above. egg and nestling predation by voles could be usual throughout their range. REFERENCES Furness. R.W. 1988. Predation of ground-nesting seabirds by is- land populations of red deer Cerims elnplius and sheep Ovis. J. Zool. Lond. 216: 565-573. Major. R.E. 199 1. Identification of nest predators by photography. dummy eggs. and adhesive tape. Auk 108: 190-195. Maxson. S.J. & Oring, L.W. 1978. Mice as a source 0 1  egg loss among ground-nesting birds. Auk 95: 582-584. Murray. K.G..  Winnet-Murray. K.. Eppley. Z.A.. Hunt. C.L. & Schwartz, D.B. 1Y83. Breeding biology ul' the Xantus' Murrelet. Condor 8 5: 12-2 1. Niethammer. J. & Krapp. F. (cds). 1978. Handbuch der Saugetiere Europas. Band I-Rodentia 1 .  Wiesbadcn: Academische Verlags- gesellshaft Wiesbaden. Obrtel. R.  81 HoliSova. V 1977. Sufficient sample sixe for analyses of small rodent diets. Folia Zool. 26: 193-205. Pedroli. J.C. 1978. Breeding success of the Meadow Pipit Aritluis prciteiisis in the Swiss Jura. Ornis Scand. 9: 168-171. Pennington. M.G. 1992. Predation of birds' cggs and chicks by herbivorous mammals. Scot. Birds 16: 285. Pialt. J.E. Roberts. B.11.. Lidster. W.W.. Wells. J.L. & Hatch. S.A. 1990. Effect of human disturbance on breeding Least and Crest- ed Auldets at St. Lawrence Island. Alaska. iiulr 107: 342- 3 50. Sealy. S.G. 1982. Voles as a source of egg and nestling loss among nesting auklets. Murrelet 63:  9-14. Verbeek, N.A.M. 1970. Breeding biology 0 1  the Water Pipit. Auk 87: 425-451. Adoption of young in the Blackbird Turdus merula The term "adoption" is defined as the provision of care to young by unrelated adults. Of the bird species studied with biparerital care. adoptive behaviour has been recorded in 17 species. and only by replacement males (Meek & Robertson 1991). Rohwer's (1986) hy- pothesis is that adoption may facilitate the replacement male ac- quiring the female for renesting (either within or between breeding seasons). It is expected that adoption will be favoured within brccd- ing seasons in double-brooded species that break the pair bond and disperse following nest failure but maintain pair bonds following 1 9 9 7  S H 0 R 1 C 0 M M U N I C A T  10 N S 1 7 5  successful nesting. Only nine studies have quantified the amount of care provided when replacement males feed young. and there are 110 documented examples of full adoption by a replacement breed- ing pair (Meek & Kobertson 1991). We record a rare case of adop- tion of young by a breeding pair in the Blackbird Turdus merulu. ohscrvcd in The Netherlands. Blackbirds are territorial. sexually dimorphic birds. Observations on thc breeding ecology of colour-ringed birds showed that only the femtrle incubate. but both parents feed the nestlings until they fledge 13-14 days after hatching (Snow 1958.  Reise 1990,  Magrath 1992, Schnack 1991) .  In the Netherlands. clutches are usually laid lroni mid-March to late June. during which time a pair can raise twtr broods. sometimes more (Snow 1958.  Glutz & Bauer 1988) .  Advptions in the Blackbird have not been reported previously (Reise 1990. Magrath 1992.  Meek & Robertson 1991. Schnack 1991) .  In May 1995 a breeding pair (male 1 and female 1 )  built a nest at ii height of 4 m in a spruce tree, 3 m from a window. which offered good opportunities for observation. Soon after the female started incubating. the male was injured by a cat. Due to damaged flight leathers in one wing and the loss of all tail feathers he was unahle to fly and after 7 week he was found dead. The female, which was also identifiable by the absence of tail feathers. remained incubating. During the first 2 days alter hatching, the female stayed on the nest lor 80% of the day and fed the young infrequently (mean feedings per hour i s.e.=0.51 2 0.05; the iiest was ob- served for N hi. Two days after hatching. another pair (male 2 and female 2) .  with undamaged plumage and therefore distinguishable from pair 1. entered the territory. When the male approached the nest. female 1 immediately flew ofr and did not defend her nestlings. However. after a brief inspection. the male started foraging and soon afterward returned to the nest with food and fed the young. During the nestling phase. he took a i0'% share of all feedings (mean feeding rate per hour, female 1 = 1.62 i 0.20: male 2 = 1.86 i 0.16; ti = h h) .  Female 1 did not show any aggressive behaviour toward male 2 or female 2. Instead, she avoided them, leaving the nest immcdiately when one of the others landed in the nest tree. but shc continued feeding her young. Female 2 did not show overt aggression toward female 7 or the young, but she fol- lowed her persistently wherever she went. Two days after the arrival of pair 2. female 2 started building her own nest 1 m above the nest built by pair 1. The male did not assist her hut only fed the young in the first nest. Female 2 laid eggs, hut her clutch was lost c. 3 (lays after she started incubation. After the clutch loss. she also adopted the young in nest 1 by feeding thcrn, though the feeding rate was low (mean feeding rate per hour = 0.32 i 0.11: II = 8 h). At least oiie nestling fledged and was k d  by male 2 away from the nest. The interpretation of the observed adoption behaviour remains speculalivc. as the degree of genetic relatedness between these in- dividuals is unknown. Obviously for female 1. receiving help at the nest IS advantageous for offspring survival. Without this help she would probably have lost her entire brood. since she would not have been able to hoth brood and feed the newly hatched young properly. Adoption by the new inale would he adaptive from his point of view when he had fathered (some of] the young by extra-pair fertilixa- tion. If the ncw male was related to female 1. his adoptive behav- iour t~ould he explained in terms of gaining indirect fitness benefits through the production of related young (Emlen 1995). I f  unrc- lated to female 1. he would gain no clear titness benefits. unless adoption served as a way of establishing a new pair bond with a high-quality partner. For female 2. adoption was not associated with obtaining breeding status: she adopted the young of female 1 after failure of her own clutch. Again. this could he adaptive for her if she was related to female 1. However. being a breeder is generally the most productive. and one might wonder why female 2 did not destroy the brood of female 1 (who seemed to be sub- missive) and expel her from the territory. By this action she might have gained better brood care from her partner, resulting in sur- viving offspring of her own. We are grateful for comments by Ben Hatchwell (Shellield Univer- sity. IJK) and Joost Tinbergen (Groningen Ilniversity. The Nether- lands). REFERENCES Emlen. S.?: 1995.  An evolutionary theory of the family. Proc. Natl. Acad. Sci. U.S.A. 92: 8092-8099. Glutz. I1.N. h; Bauer, K.M. 1988. Handbuch der Vbgel Mitteleuro- pas 11 /It. Wiesbaden: "LA-Verlag. Magrath, R.D. 1992. Seasonal changes in egg-mass within and among clutches of birds: General explanations and a field study of the Blackbird T~rrdus rnerula. Ibis 134: 171-179. Meek, S.B. & Robertson. K.J. 1991.  Adoption of young by replace- ment male birds: An experimental study of eastern bluebirds and a review. Anim. Behav. 42: 81 3-820. Kcise, H. 1990. Observations on ecology and biology of the Hlack- bird (Turdus tnerula) in the Leipxig City (Poland). Zoologische Ab- handlungen (Dresden) 45(9-19): 155-1 78. Rohwer. S. 1986.  Selection for adoption versus infanticide by re- placement 'mates' in birds. Current Ornith. 3 :  353-395. Schnack. S. 1991.  The breeding hiology arid nestling diet of the Blackbird Turdus rrierula 1,. and the Song Thrush Turdus pliilorlir- IIOS C.L. Brelini in Vienna and in a n  adjacent wood. Acta Orn. Warsz. 26(2): 85-106. Snow, D.W. 1958.  A Study of Blackbirds. London: Allen K. Uiiwin. Srrbrriittrrl 2 0  kbrurwy 1996; rrvisiori accepted 20 ilflarrli 1996 Habitat selection by marine birds in relation to water depth A recent analysis of seabird abundance in relation to water depth (Stone et crl. 1995)  showed that some species (auks and Manx Shearwaters Puffirius prffinirs) were restricted largely to continental shelf waters less than 1 0 0  m in depth. while other species (Fulmars 

University of Groningen Research Database

  
 University of Groningen
Adoption of young in the Blackbird Turdus merula
Dijkstra, Eelco; Komdeur, Jan; Dijkstra, Cor
Published in:
Ibis
IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from
it. Please check the document version below.
Document Version
Publisher's PDF, also known as Version of record
Publication date:
1997
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):
Dijkstra, E., Komdeur, J., & Dijkstra, C. (1997). Adoption of young in the Blackbird Turdus merula. Ibis,
139(1), 174-175.
Copyright
Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the
author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).
Take-down policy
If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately
and investigate your claim.
Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the
number of authors shown on this cover page is limited to 10 maximum.
Download date: 10-02-2018
1 7 4  S H O R T  C O M  M I J N  I C A ' r I  ( I N S  I R I S  1 3 9  
Egg Total Nestling Total 
predation predation 
predation by voles by voles 
predation Hatched nestling Vole Total Un- 
nest- Total egg 
predation (No. found eggs lings 
dcnsity eggs hatched by voles 
Year pcr h a )  I )  n n ' X ,  n '%, n II '%, I 1  '%I I 1  '%, 
1993 40 132 10 22 17 18 14 100 16 16 12 12 30 22.7 
7994 1 5  1 3 3  9 27 20 1 3  10 97 18 19 9 9 22 16.5 
1 W i  4 134 6 11 8 7 5 117 20 17 5 4 12 9.0 
I+edatio~i by voles detected by a video camera and by other signs as described in the text. 
cad i  (trodden by Chamois Hirpicnpm nrpicapm and bitten by Carabid 
bcctlcs) were placed 30-100 cm from vole burrows. The nestlings 
wc'rc 3 davs and 7 days old and weighed 3.559 g. A video camera 
w.ts locused on the nest (in one instance a 500-mm lens was used 
to photograph from a hide). 'I'he study was carried out in June 
1 OY 5. 
In each ciise the C'ominon Voles took both the eggs and the nest- 
Iiiigs into their burrows. 'I'he nestlings were bitten on the head and 
immediately pulled into the burrows. None of the nests were dis- 
turbed by the voles. The removal of the prey from these nests which 
Mere less well concealed than natural nests. into burrows was prob- 
ably inlluenced by the vole's antipredator behaviour. In addition, 
pieces of eggshells. egg contents soaked into the nest and vole drop- 
pings were found in about half of the natural pipit nests. which 
werc mainly well hidden. examined. Partially devoured nestlings 
wcre sporadically found in nests. and they were sometimes fouiid 
i i i  the grass near the nests. Parts of their bodies. often the head 
and legs. were partly devoured. In most cases. the nestlings had 
been Idled by a bite through the skull. 
l'he predation on Meadow Pipit eggs and nestlings changed with 
the density of' the voles during their cycle of numbers. The voles 
wcrc the most important predators during the vole outbreak (Table 
1 ). The approximate spring density of voles was estimated from the 
iiumber of observed occupied burrows found on a strip transect 
I 300 X L m). Verbeek (1970) recorded similar signs of Deer Mouse 
predation on Water Pipit eggs and nestlings. Again. the predation 
oii cggs was much higher when the Deer Mice were plentiful. 
I'he results confirm the suggestion of Piatt et ( 1 1 .  (1990) that the 
disappearance of eggs and nestlings could have been caused by 
WJICS. I3ased on the results above. egg and nestling predation by 
voles could be usual throughout their range. 
REFERENCES 
Furness. R.W. 1988. Predation of ground-nesting seabirds by is- 
land populations of red deer Cerims elnplius and sheep Ovis. J. 
Zool. Lond. 216: 565-573. 
Major. R.E. 199 1. Identification of nest predators by photography. 
dummy eggs. and adhesive tape. Auk 108: 190-195. 
Maxson. S.J. & Oring, L.W. 1978. Mice as a source 0 1  egg loss 
among ground-nesting birds. Auk 95: 582-584. 
Murray. K.G..  Winnet-Murray. K.. Eppley. Z.A.. Hunt. C.L. & 
Schwartz, D.B. 1Y83. Breeding biology ul' the Xantus' Murrelet. 
Condor 8 5: 12-2 1. 
Niethammer. J. & Krapp. F. (cds). 1978. Handbuch der Saugetiere 
Europas. Band I-Rodentia 1 .  Wiesbadcn: Academische Verlags- 
gesellshaft Wiesbaden. 
Obrtel. R.  81 HoliSova. V 1977. Sufficient sample sixe for analyses 
of small rodent diets. Folia Zool. 26: 193-205. 
Pedroli. J.C. 1978. Breeding success of the Meadow Pipit Aritluis 
prciteiisis in the Swiss Jura. Ornis Scand. 9: 168-171. 
Pennington. M.G. 1992. Predation of birds' cggs and chicks by 
herbivorous mammals. Scot. Birds 16: 285. 
Pialt. J.E. Roberts. B.11.. Lidster. W.W.. Wells. J.L. & Hatch. S.A. 
1990. Effect of human disturbance on breeding Least and Crest- 
ed Auldets at St. Lawrence Island. Alaska. iiulr 107: 342- 3 50. 
Sealy. S.G. 1982. Voles as a source of egg and nestling loss among 
nesting auklets. Murrelet 63:  9-14. 
Verbeek, N.A.M. 1970. Breeding biology 0 1  the Water Pipit. Auk 
87: 425-451. 
Adoption of young in the Blackbird 
Turdus merula 
The term "adoption" is defined as the provision of care to young 
by unrelated adults. Of the bird species studied with biparerital care. 
adoptive behaviour has been recorded in 17 species. and only by 
replacement males (Meek & Robertson 1991). Rohwer's (1986) hy- 
pothesis is that adoption may facilitate the replacement male ac- 
quiring the female for renesting (either within or between breeding 
seasons). It is expected that adoption will be favoured within brccd- 
ing seasons in double-brooded species that break the pair bond and 
disperse following nest failure but maintain pair bonds following 
1 9 9 7  S H 0 R 1 C 0 M M U N I C A T  10 N S 1 7 5  
successful nesting. Only nine studies have quantified the amount of 
care provided when replacement males feed young. and there are 
110 documented examples of full adoption by a replacement breed- 
ing pair (Meek & Kobertson 1991). We record a rare case of adop- 
tion of young by a breeding pair in the Blackbird Turdus merulu. 
ohscrvcd in The Netherlands. 
Blackbirds are territorial. sexually dimorphic birds. Observations 
on thc breeding ecology of colour-ringed birds showed that only the 
femtrle incubate. but both parents feed the nestlings until they fledge 
13-14 days after hatching (Snow 1958.  Reise 1990,  Magrath 
1992, Schnack 1991) .  In the Netherlands. clutches are usually laid 
lroni mid-March to late June. during which time a pair can raise 
twtr broods. sometimes more (Snow 1958.  Glutz & Bauer 1988) .  
Advptions in the Blackbird have not been reported previously (Reise 
1990. Magrath 1992.  Meek & Robertson 1991. Schnack 1991) .  
In May 1995 a breeding pair (male 1 and female 1 )  built a nest 
at ii height of 4 m in a spruce tree, 3 m from a window. which 
offered good opportunities for observation. Soon after the female 
started incubating. the male was injured by a cat. Due to damaged 
flight leathers in one wing and the loss of all tail feathers he was 
unahle to fly and after 7 week he was found dead. The female, 
which was also identifiable by the absence of tail feathers. remained 
incubating. During the first 2 days alter hatching, the female stayed 
on the nest lor 80% of the day and fed the young infrequently 
(mean feedings per hour i s.e.=0.51 2 0.05; the iiest was ob- 
served for N hi. Two days after hatching. another pair (male 2 and 
female 2) .  with undamaged plumage and therefore distinguishable 
from pair 1. entered the territory. When the male approached the 
nest. female 1 immediately flew ofr and did not defend her nestlings. 
However. after a brief inspection. the male started foraging and 
soon afterward returned to the nest with food and fed the young. 
During the nestling phase. he took a i0'% share of all feedings 
(mean feeding rate per hour, female 1 = 1.62 i 0.20: male 2 = 
1.86 i 0.16; ti = h h) .  Female 1 did not show any aggressive 
behaviour toward male 2 or female 2. Instead, she avoided them, 
leaving the nest immcdiately when one of the others landed in the 
nest tree. but shc continued feeding her young. Female 2 did not 
show overt aggression toward female 7 or the young, but she fol- 
lowed her persistently wherever she went. Two days after the arrival 
of pair 2. female 2 started building her own nest 1 m above the 
nest built by pair 1. The male did not assist her hut only fed the 
young in the first nest. Female 2 laid eggs, hut her clutch was lost 
c. 3 (lays after she started incubation. After the clutch loss. she also 
adopted the young in nest 1 by feeding thcrn, though the feeding 
rate was low (mean feeding rate per hour = 0.32 i 0.11: II = 8 
h). At least oiie nestling fledged and was k d  by male 2 away from 
the nest. 
The interpretation of the observed adoption behaviour remains 
speculalivc. as the degree of genetic relatedness between these in- 
dividuals is unknown. Obviously for female 1. receiving help at the 
nest IS advantageous for offspring survival. Without this help she 
would probably have lost her entire brood. since she would not have 
been able to hoth brood and feed the newly hatched young properly. 
Adoption by the new inale would he adaptive from his point of view 
when he had fathered (some of] the young by extra-pair fertilixa- 
tion. If the ncw male was related to female 1. his adoptive behav- 
iour t~ould he explained in terms of gaining indirect fitness benefits 
through the production of related young (Emlen 1995). I f  unrc- 
lated to female 1. he would gain no clear titness benefits. unless 
adoption served as a way of establishing a new pair bond with a 
high-quality partner. For female 2. adoption was not associated 
with obtaining breeding status: she adopted the young of female 1 
after failure of her own clutch. Again. this could he adaptive for 
her if she was related to female 1. However. being a breeder is 
generally the most productive. and one might wonder why female 
2 did not destroy the brood of female 1 (who seemed to be sub- 
missive) and expel her from the territory. By this action she might 
have gained better brood care from her partner, resulting in sur- 
viving offspring of her own. 
We are grateful for comments by Ben Hatchwell (Shellield Univer- 
sity. IJK) and Joost Tinbergen (Groningen Ilniversity. The Nether- 
lands). 
REFERENCES 
Emlen. S.?: 1995.  An evolutionary theory of the family. Proc. Natl. 
Acad. Sci. U.S.A. 92: 8092-8099. 
Glutz. I1.N. h; Bauer, K.M. 1988. Handbuch der Vbgel Mitteleuro- 
pas 11 /It. Wiesbaden: "LA-Verlag. 
Magrath, R.D. 1992. Seasonal changes in egg-mass within and 
among clutches of birds: General explanations and a field study 
of the Blackbird T~rrdus rnerula. Ibis 134: 171-179. 
Meek, S.B. & Robertson. K.J. 1991.  Adoption of young by replace- 
ment male birds: An experimental study of eastern bluebirds and 
a review. Anim. Behav. 42: 81 3-820. 
Kcise, H. 1990. Observations on ecology and biology of the Hlack- 
bird (Turdus tnerula) in the Leipxig City (Poland). Zoologische Ab- 
handlungen (Dresden) 45(9-19): 155-1 78. 
Rohwer. S. 1986.  Selection for adoption versus infanticide by re- 
placement 'mates' in birds. Current Ornith. 3 :  353-395. 
Schnack. S. 1991.  The breeding hiology arid nestling diet of the 
Blackbird Turdus rrierula 1,. and the Song Thrush Turdus pliilorlir- 
IIOS C.L. Brelini in Vienna and in a n  adjacent wood. Acta Orn. 
Warsz. 26(2): 85-106. 
Snow, D.W. 1958.  A Study of Blackbirds. London: Allen K. Uiiwin. 
Srrbrriittrrl 2 0  kbrurwy 1996; rrvisiori accepted 20 ilflarrli 1996 
Habitat selection by marine birds in 
relation to water depth 
A recent analysis of seabird abundance in relation to water depth 
(Stone et crl. 1995)  showed that some species (auks and Manx 
Shearwaters Puffirius prffinirs) were restricted largely to continental 
shelf waters less than 1 0 0  m in depth. while other species (Fulmars 


   University of GroningenAdoption of young in the Blackbird Turdus merulaDijkstra, Eelco; Komdeur, Jan; Dijkstra, CorPublished in:IbisIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1997Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Dijkstra, E., Komdeur, J., & Dijkstra, C. (1997). Adoption of young in the Blackbird Turdus merula. Ibis,139(1), 174-175.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 06-06-20221 7 4  S H O R T  C O M  M I J N  I C A ' r I  ( I N S  I R I S  1 3 9  Egg Total Nestling Total predation predation predation by voles by voles predation Hatched nestling Vole Total Un- nest- Total egg predation (No. found eggs lings dcnsity eggs hatched by voles Year pcr h a )  I )  n n ' X ,  n '%, n II '%, I 1  '%I I 1  '%, 1993 40 132 10 22 17 18 14 100 16 16 12 12 30 22.7 7994 1 5  1 3 3  9 27 20 1 3  10 97 18 19 9 9 22 16.5 1 W i  4 134 6 11 8 7 5 117 20 17 5 4 12 9.0 I+edatio~i by voles detected by a video camera and by other signs as described in the text. cad i  (trodden by Chamois Hirpicnpm nrpicapm and bitten by Carabid bcctlcs) were placed 30-100 cm from vole burrows. The nestlings wc'rc 3 davs and 7 days old and weighed 3.559 g. A video camera w.ts locused on the nest (in one instance a 500-mm lens was used to photograph from a hide). 'I'he study was carried out in June 1 OY 5. In each ciise the C'ominon Voles took both the eggs and the nest- Iiiigs into their burrows. 'I'he nestlings were bitten on the head and immediately pulled into the burrows. None of the nests were dis- turbed by the voles. The removal of the prey from these nests which Mere less well concealed than natural nests. into burrows was prob- ably inlluenced by the vole's antipredator behaviour. In addition, pieces of eggshells. egg contents soaked into the nest and vole drop- pings were found in about half of the natural pipit nests. which werc mainly well hidden. examined. Partially devoured nestlings wcre sporadically found in nests. and they were sometimes fouiid i i i  the grass near the nests. Parts of their bodies. often the head and legs. were partly devoured. In most cases. the nestlings had been Idled by a bite through the skull. l'he predation on Meadow Pipit eggs and nestlings changed with the density of' the voles during their cycle of numbers. The voles wcrc the most important predators during the vole outbreak (Table 1 ). The approximate spring density of voles was estimated from the iiumber of observed occupied burrows found on a strip transect I 300 X L m). Verbeek (1970) recorded similar signs of Deer Mouse predation on Water Pipit eggs and nestlings. Again. the predation oii cggs was much higher when the Deer Mice were plentiful. I'he results confirm the suggestion of Piatt et ( 1 1 .  (1990) that the disappearance of eggs and nestlings could have been caused by WJICS. I3ased on the results above. egg and nestling predation by voles could be usual throughout their range. REFERENCES Furness. R.W. 1988. Predation of ground-nesting seabirds by is- land populations of red deer Cerims elnplius and sheep Ovis. J. Zool. Lond. 216: 565-573. Major. R.E. 199 1. Identification of nest predators by photography. dummy eggs. and adhesive tape. Auk 108: 190-195. Maxson. S.J. & Oring, L.W. 1978. Mice as a source 0 1  egg loss among ground-nesting birds. Auk 95: 582-584. Murray. K.G..  Winnet-Murray. K.. Eppley. Z.A.. Hunt. C.L. & Schwartz, D.B. 1Y83. Breeding biology ul' the Xantus' Murrelet. Condor 8 5: 12-2 1. Niethammer. J. & Krapp. F. (cds). 1978. Handbuch der Saugetiere Europas. Band I-Rodentia 1 .  Wiesbadcn: Academische Verlags- gesellshaft Wiesbaden. Obrtel. R.  81 HoliSova. V 1977. Sufficient sample sixe for analyses of small rodent diets. Folia Zool. 26: 193-205. Pedroli. J.C. 1978. Breeding success of the Meadow Pipit Aritluis prciteiisis in the Swiss Jura. Ornis Scand. 9: 168-171. Pennington. M.G. 1992. Predation of birds' cggs and chicks by herbivorous mammals. Scot. Birds 16: 285. Pialt. J.E. Roberts. B.11.. Lidster. W.W.. Wells. J.L. & Hatch. S.A. 1990. Effect of human disturbance on breeding Least and Crest- ed Auldets at St. Lawrence Island. Alaska. iiulr 107: 342- 3 50. Sealy. S.G. 1982. Voles as a source of egg and nestling loss among nesting auklets. Murrelet 63:  9-14. Verbeek, N.A.M. 1970. Breeding biology 0 1  the Water Pipit. Auk 87: 425-451. Adoption of young in the Blackbird Turdus merula The term "adoption" is defined as the provision of care to young by unrelated adults. Of the bird species studied with biparerital care. adoptive behaviour has been recorded in 17 species. and only by replacement males (Meek & Robertson 1991). Rohwer's (1986) hy- pothesis is that adoption may facilitate the replacement male ac- quiring the female for renesting (either within or between breeding seasons). It is expected that adoption will be favoured within brccd- ing seasons in double-brooded species that break the pair bond and disperse following nest failure but maintain pair bonds following 1 9 9 7  S H 0 R 1 C 0 M M U N I C A T  10 N S 1 7 5  successful nesting. Only nine studies have quantified the amount of care provided when replacement males feed young. and there are 110 documented examples of full adoption by a replacement breed- ing pair (Meek & Kobertson 1991). We record a rare case of adop- tion of young by a breeding pair in the Blackbird Turdus merulu. ohscrvcd in The Netherlands. Blackbirds are territorial. sexually dimorphic birds. Observations on thc breeding ecology of colour-ringed birds showed that only the femtrle incubate. but both parents feed the nestlings until they fledge 13-14 days after hatching (Snow 1958.  Reise 1990,  Magrath 1992, Schnack 1991) .  In the Netherlands. clutches are usually laid lroni mid-March to late June. during which time a pair can raise twtr broods. sometimes more (Snow 1958.  Glutz & Bauer 1988) .  Advptions in the Blackbird have not been reported previously (Reise 1990. Magrath 1992.  Meek & Robertson 1991. Schnack 1991) .  In May 1995 a breeding pair (male 1 and female 1 )  built a nest at ii height of 4 m in a spruce tree, 3 m from a window. which offered good opportunities for observation. Soon after the female started incubating. the male was injured by a cat. Due to damaged flight leathers in one wing and the loss of all tail feathers he was unahle to fly and after 7 week he was found dead. The female, which was also identifiable by the absence of tail feathers. remained incubating. During the first 2 days alter hatching, the female stayed on the nest lor 80% of the day and fed the young infrequently (mean feedings per hour i s.e.=0.51 2 0.05; the iiest was ob- served for N hi. Two days after hatching. another pair (male 2 and female 2) .  with undamaged plumage and therefore distinguishable from pair 1. entered the territory. When the male approached the nest. female 1 immediately flew ofr and did not defend her nestlings. However. after a brief inspection. the male started foraging and soon afterward returned to the nest with food and fed the young. During the nestling phase. he took a i0'% share of all feedings (mean feeding rate per hour, female 1 = 1.62 i 0.20: male 2 = 1.86 i 0.16; ti = h h) .  Female 1 did not show any aggressive behaviour toward male 2 or female 2. Instead, she avoided them, leaving the nest immcdiately when one of the others landed in the nest tree. but shc continued feeding her young. Female 2 did not show overt aggression toward female 7 or the young, but she fol- lowed her persistently wherever she went. Two days after the arrival of pair 2. female 2 started building her own nest 1 m above the nest built by pair 1. The male did not assist her hut only fed the young in the first nest. Female 2 laid eggs, hut her clutch was lost c. 3 (lays after she started incubation. After the clutch loss. she also adopted the young in nest 1 by feeding thcrn, though the feeding rate was low (mean feeding rate per hour = 0.32 i 0.11: II = 8 h). At least oiie nestling fledged and was k d  by male 2 away from the nest. The interpretation of the observed adoption behaviour remains speculalivc. as the degree of genetic relatedness between these in- dividuals is unknown. Obviously for female 1. receiving help at the nest IS advantageous for offspring survival. Without this help she would probably have lost her entire brood. since she would not have been able to hoth brood and feed the newly hatched young properly. Adoption by the new inale would he adaptive from his point of view when he had fathered (some of] the young by extra-pair fertilixa- tion. If the ncw male was related to female 1. his adoptive behav- iour t~ould he explained in terms of gaining indirect fitness benefits through the production of related young (Emlen 1995). I f  unrc- lated to female 1. he would gain no clear titness benefits. unless adoption served as a way of establishing a new pair bond with a high-quality partner. For female 2. adoption was not associated with obtaining breeding status: she adopted the young of female 1 after failure of her own clutch. Again. this could he adaptive for her if she was related to female 1. However. being a breeder is generally the most productive. and one might wonder why female 2 did not destroy the brood of female 1 (who seemed to be sub- missive) and expel her from the territory. By this action she might have gained better brood care from her partner, resulting in sur- viving offspring of her own. We are grateful for comments by Ben Hatchwell (Shellield Univer- sity. IJK) and Joost Tinbergen (Groningen Ilniversity. The Nether- lands). REFERENCES Emlen. S.?: 1995.  An evolutionary theory of the family. Proc. Natl. Acad. Sci. U.S.A. 92: 8092-8099. Glutz. I1.N. h; Bauer, K.M. 1988. Handbuch der Vbgel Mitteleuro- pas 11 /It. Wiesbaden: "LA-Verlag. Magrath, R.D. 1992. Seasonal changes in egg-mass within and among clutches of birds: General explanations and a field study of the Blackbird T~rrdus rnerula. Ibis 134: 171-179. Meek, S.B. & Robertson. K.J. 1991.  Adoption of young by replace- ment male birds: An experimental study of eastern bluebirds and a review. Anim. Behav. 42: 81 3-820. Kcise, H. 1990. Observations on ecology and biology of the Hlack- bird (Turdus tnerula) in the Leipxig City (Poland). Zoologische Ab- handlungen (Dresden) 45(9-19): 155-1 78. Rohwer. S. 1986.  Selection for adoption versus infanticide by re- placement 'mates' in birds. Current Ornith. 3 :  353-395. Schnack. S. 1991.  The breeding hiology arid nestling diet of the Blackbird Turdus rrierula 1,. and the Song Thrush Turdus pliilorlir- IIOS C.L. Brelini in Vienna and in a n  adjacent wood. Acta Orn. Warsz. 26(2): 85-106. Snow, D.W. 1958.  A Study of Blackbirds. London: Allen K. Uiiwin. Srrbrriittrrl 2 0  kbrurwy 1996; rrvisiori accepted 20 ilflarrli 1996 Habitat selection by marine birds in relation to water depth A recent analysis of seabird abundance in relation to water depth (Stone et crl. 1995)  showed that some species (auks and Manx Shearwaters Puffirius prffinirs) were restricted largely to continental shelf waters less than 1 0 0  m in depth. while other species (Fulmars 

NARCIS 

   University of GroningenAdoption of young in the Blackbird Turdus merulaDijkstra, Eelco; Komdeur, Jan; Dijkstra, CorPublished in:IbisIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1997Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Dijkstra, E., Komdeur, J., & Dijkstra, C. (1997). Adoption of young in the Blackbird Turdus merula. Ibis,139(1), 174-175.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 04-06-20221 7 4  S H O R T  C O M  M I J N  I C A ' r I  ( I N S  I R I S  1 3 9  Egg Total Nestling Total predation predation predation by voles by voles predation Hatched nestling Vole Total Un- nest- Total egg predation (No. found eggs lings dcnsity eggs hatched by voles Year pcr h a )  I )  n n ' X ,  n '%, n II '%, I 1  '%I I 1  '%, 1993 40 132 10 22 17 18 14 100 16 16 12 12 30 22.7 7994 1 5  1 3 3  9 27 20 1 3  10 97 18 19 9 9 22 16.5 1 W i  4 134 6 11 8 7 5 117 20 17 5 4 12 9.0 I+edatio~i by voles detected by a video camera and by other signs as described in the text. cad i  (trodden by Chamois Hirpicnpm nrpicapm and bitten by Carabid bcctlcs) were placed 30-100 cm from vole burrows. The nestlings wc'rc 3 davs and 7 days old and weighed 3.559 g. A video camera w.ts locused on the nest (in one instance a 500-mm lens was used to photograph from a hide). 'I'he study was carried out in June 1 OY 5. In each ciise the C'ominon Voles took both the eggs and the nest- Iiiigs into their burrows. 'I'he nestlings were bitten on the head and immediately pulled into the burrows. None of the nests were dis- turbed by the voles. The removal of the prey from these nests which Mere less well concealed than natural nests. into burrows was prob- ably inlluenced by the vole's antipredator behaviour. In addition, pieces of eggshells. egg contents soaked into the nest and vole drop- pings were found in about half of the natural pipit nests. which werc mainly well hidden. examined. Partially devoured nestlings wcre sporadically found in nests. and they were sometimes fouiid i i i  the grass near the nests. Parts of their bodies. often the head and legs. were partly devoured. In most cases. the nestlings had been Idled by a bite through the skull. l'he predation on Meadow Pipit eggs and nestlings changed with the density of' the voles during their cycle of numbers. The voles wcrc the most important predators during the vole outbreak (Table 1 ). The approximate spring density of voles was estimated from the iiumber of observed occupied burrows found on a strip transect I 300 X L m). Verbeek (1970) recorded similar signs of Deer Mouse predation on Water Pipit eggs and nestlings. Again. the predation oii cggs was much higher when the Deer Mice were plentiful. I'he results confirm the suggestion of Piatt et ( 1 1 .  (1990) that the disappearance of eggs and nestlings could have been caused by WJICS. I3ased on the results above. egg and nestling predation by voles could be usual throughout their range. REFERENCES Furness. R.W. 1988. Predation of ground-nesting seabirds by is- land populations of red deer Cerims elnplius and sheep Ovis. J. Zool. Lond. 216: 565-573. Major. R.E. 199 1. Identification of nest predators by photography. dummy eggs. and adhesive tape. Auk 108: 190-195. Maxson. S.J. & Oring, L.W. 1978. Mice as a source 0 1  egg loss among ground-nesting birds. Auk 95: 582-584. Murray. K.G..  Winnet-Murray. K.. Eppley. Z.A.. Hunt. C.L. & Schwartz, D.B. 1Y83. Breeding biology ul' the Xantus' Murrelet. Condor 8 5: 12-2 1. Niethammer. J. & Krapp. F. (cds). 1978. Handbuch der Saugetiere Europas. Band I-Rodentia 1 .  Wiesbadcn: Academische Verlags- gesellshaft Wiesbaden. Obrtel. R.  81 HoliSova. V 1977. Sufficient sample sixe for analyses of small rodent diets. Folia Zool. 26: 193-205. Pedroli. J.C. 1978. Breeding success of the Meadow Pipit Aritluis prciteiisis in the Swiss Jura. Ornis Scand. 9: 168-171. Pennington. M.G. 1992. Predation of birds' cggs and chicks by herbivorous mammals. Scot. Birds 16: 285. Pialt. J.E. Roberts. B.11.. Lidster. W.W.. Wells. J.L. & Hatch. S.A. 1990. Effect of human disturbance on breeding Least and Crest- ed Auldets at St. Lawrence Island. Alaska. iiulr 107: 342- 3 50. Sealy. S.G. 1982. Voles as a source of egg and nestling loss among nesting auklets. Murrelet 63:  9-14. Verbeek, N.A.M. 1970. Breeding biology 0 1  the Water Pipit. Auk 87: 425-451. Adoption of young in the Blackbird Turdus merula The term "adoption" is defined as the provision of care to young by unrelated adults. Of the bird species studied with biparerital care. adoptive behaviour has been recorded in 17 species. and only by replacement males (Meek & Robertson 1991). Rohwer's (1986) hy- pothesis is that adoption may facilitate the replacement male ac- quiring the female for renesting (either within or between breeding seasons). It is expected that adoption will be favoured within brccd- ing seasons in double-brooded species that break the pair bond and disperse following nest failure but maintain pair bonds following 1 9 9 7  S H 0 R 1 C 0 M M U N I C A T  10 N S 1 7 5  successful nesting. Only nine studies have quantified the amount of care provided when replacement males feed young. and there are 110 documented examples of full adoption by a replacement breed- ing pair (Meek & Kobertson 1991). We record a rare case of adop- tion of young by a breeding pair in the Blackbird Turdus merulu. ohscrvcd in The Netherlands. Blackbirds are territorial. sexually dimorphic birds. Observations on thc breeding ecology of colour-ringed birds showed that only the femtrle incubate. but both parents feed the nestlings until they fledge 13-14 days after hatching (Snow 1958.  Reise 1990,  Magrath 1992, Schnack 1991) .  In the Netherlands. clutches are usually laid lroni mid-March to late June. during which time a pair can raise twtr broods. sometimes more (Snow 1958.  Glutz & Bauer 1988) .  Advptions in the Blackbird have not been reported previously (Reise 1990. Magrath 1992.  Meek & Robertson 1991. Schnack 1991) .  In May 1995 a breeding pair (male 1 and female 1 )  built a nest at ii height of 4 m in a spruce tree, 3 m from a window. which offered good opportunities for observation. Soon after the female started incubating. the male was injured by a cat. Due to damaged flight leathers in one wing and the loss of all tail feathers he was unahle to fly and after 7 week he was found dead. The female, which was also identifiable by the absence of tail feathers. remained incubating. During the first 2 days alter hatching, the female stayed on the nest lor 80% of the day and fed the young infrequently (mean feedings per hour i s.e.=0.51 2 0.05; the iiest was ob- served for N hi. Two days after hatching. another pair (male 2 and female 2) .  with undamaged plumage and therefore distinguishable from pair 1. entered the territory. When the male approached the nest. female 1 immediately flew ofr and did not defend her nestlings. However. after a brief inspection. the male started foraging and soon afterward returned to the nest with food and fed the young. During the nestling phase. he took a i0'% share of all feedings (mean feeding rate per hour, female 1 = 1.62 i 0.20: male 2 = 1.86 i 0.16; ti = h h) .  Female 1 did not show any aggressive behaviour toward male 2 or female 2. Instead, she avoided them, leaving the nest immcdiately when one of the others landed in the nest tree. but shc continued feeding her young. Female 2 did not show overt aggression toward female 7 or the young, but she fol- lowed her persistently wherever she went. Two days after the arrival of pair 2. female 2 started building her own nest 1 m above the nest built by pair 1. The male did not assist her hut only fed the young in the first nest. Female 2 laid eggs, hut her clutch was lost c. 3 (lays after she started incubation. After the clutch loss. she also adopted the young in nest 1 by feeding thcrn, though the feeding rate was low (mean feeding rate per hour = 0.32 i 0.11: II = 8 h). At least oiie nestling fledged and was k d  by male 2 away from the nest. The interpretation of the observed adoption behaviour remains speculalivc. as the degree of genetic relatedness between these in- dividuals is unknown. Obviously for female 1. receiving help at the nest IS advantageous for offspring survival. Without this help she would probably have lost her entire brood. since she would not have been able to hoth brood and feed the newly hatched young properly. Adoption by the new inale would he adaptive from his point of view when he had fathered (some of] the young by extra-pair fertilixa- tion. If the ncw male was related to female 1. his adoptive behav- iour t~ould he explained in terms of gaining indirect fitness benefits through the production of related young (Emlen 1995). I f  unrc- lated to female 1. he would gain no clear titness benefits. unless adoption served as a way of establishing a new pair bond with a high-quality partner. For female 2. adoption was not associated with obtaining breeding status: she adopted the young of female 1 after failure of her own clutch. Again. this could he adaptive for her if she was related to female 1. However. being a breeder is generally the most productive. and one might wonder why female 2 did not destroy the brood of female 1 (who seemed to be sub- missive) and expel her from the territory. By this action she might have gained better brood care from her partner, resulting in sur- viving offspring of her own. We are grateful for comments by Ben Hatchwell (Shellield Univer- sity. IJK) and Joost Tinbergen (Groningen Ilniversity. The Nether- lands). REFERENCES Emlen. S.?: 1995.  An evolutionary theory of the family. Proc. Natl. Acad. Sci. U.S.A. 92: 8092-8099. Glutz. I1.N. h; Bauer, K.M. 1988. Handbuch der Vbgel Mitteleuro- pas 11 /It. Wiesbaden: "LA-Verlag. Magrath, R.D. 1992. Seasonal changes in egg-mass within and among clutches of birds: General explanations and a field study of the Blackbird T~rrdus rnerula. Ibis 134: 171-179. Meek, S.B. & Robertson. K.J. 1991.  Adoption of young by replace- ment male birds: An experimental study of eastern bluebirds and a review. Anim. Behav. 42: 81 3-820. Kcise, H. 1990. Observations on ecology and biology of the Hlack- bird (Turdus tnerula) in the Leipxig City (Poland). Zoologische Ab- handlungen (Dresden) 45(9-19): 155-1 78. Rohwer. S. 1986.  Selection for adoption versus infanticide by re- placement 'mates' in birds. Current Ornith. 3 :  353-395. Schnack. S. 1991.  The breeding hiology arid nestling diet of the Blackbird Turdus rrierula 1,. and the Song Thrush Turdus pliilorlir- IIOS C.L. Brelini in Vienna and in a n  adjacent wood. Acta Orn. Warsz. 26(2): 85-106. Snow, D.W. 1958.  A Study of Blackbirds. London: Allen K. Uiiwin. Srrbrriittrrl 2 0  kbrurwy 1996; rrvisiori accepted 20 ilflarrli 1996 Habitat selection by marine birds in relation to water depth A recent analysis of seabird abundance in relation to water depth (Stone et crl. 1995)  showed that some species (auks and Manx Shearwaters Puffirius prffinirs) were restricted largely to continental shelf waters less than 1 0 0  m in depth. while other species (Fulmars 

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Adoption of young in the Blackbird Turdus merula

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