Fil: Fraga, Rosendo Manuel. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; Argentin

Fraga, Rosendo Manuel

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299SHORT COMMUNICATIONSORNITOLOGIA NEOTROPICAL 19: 299–303, 2008©  The Neotropical Ornithological SocietyNOTES ON THE NESTING OF CHOPI BLACKBIRDS (GNORIMOPSAR CHOPI) IN ARGENTINA AND PARAGUAY, WITH DATA ON COOPERATIVE BREEDING AND BROOD PARASITISM BY SCREAMING COWBIRDS (MOLOTHRUS RUFOAXILLARIS)Rosendo M. FragaCICYTTP, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Matteri y España, (3105) Diamante, Entre Ríos, Argentina. E-mail: chfraga@yahoo.comNotas sobre la nidificación del Chopí (Gnorimopsar chopi) en Argentina y Paraguay, con datosde cría cooperativa y de parasitismo de cría por el Tordo Pico Corto (Molothrus rufoaxillaris).Key words: Chopi Blackbirds, Gnorimopsar chopi, nesting, cooperative breeding, Screaming Cowbird,Molothrus rufoaxillaris. The Chopi Blackbird (Gnorimopsar chopi) is anicterid endemic to South America (Jaramillo& Burke 1999) and a member of the SouthAmerican quiscaline clade, a monophyleticgroup defined by DNA data (Johnson &Lanyon 1999, Cadena et al. 2004). This icteridis found from northeastern Brazil and south-eastern Peru to northern Argentina and Uru-guay (Jaramillo & Burke 1999). It is usuallysubdivided into three subspecies with consid-erable variation in body size (Jaramillo &Burke 1999), but only the nominate subspe-cies occurs in eastern Argentina and Paraguay.Few first hand reports on the natural historyand breeding behavior of Chopi Blackbirdsexist (Azara 1802, de la Peña 1987, Sick 1993,Fraga 1996, Di Giacomo 2005), and only twonests have been described from Paraguay(Dalgleish 1899). I present here new informa-tion obtained from 12 nests observed innortheastern Argentina (Corrientes and Mis-iones provinces) and Paraguay, between 1995and 2007. My data show this icterid to be acooperative breeder (Brown 1987), as individ-uals other than a single pair aid in chick care.Also, I add further information on its host-parasite interactions with Screaming Cow-birds (Molothrus rufoaxillaris) in Argentina andParaguay (Sick 1985, Fraga 1996). I obtained most of my information onChopi Blackbirds while carrying field researchon endangered grassland birds from easternArgentina and Paraguay (Fraga 2005). ChopiBlackbirds were easy to detect by their loudsongs and other vocalizations, and nested inthe open habitats I surveyed. Observationtimes for each breeding pair or group rangedfrom 45 to 180 min, but subsequent visits tothe nests were often impossible. Chopi Black-birds are sexually monomorphic in plumage.300FRAGABody mass data from two male and twofemale specimens (American Museum ofNatural History, New York) collected inPuerto Valle (Corrientes) give values of 73.8and 74.1 g (mean 73. 9 g) for males, and 68.5and 70.8 g (mean 69.6 g) for females. Becauseof this small size dimorphism the sexes couldnot be separated in the field. As no individu-als were banded, the group size I report foreach nest was the maximum number of indi-viduals simultaneously observed. Theexposed location of most nest sites facilitatedbehavioral observations, supplemented withthe help of tape recordings.Chopi Blackbirds avoid dense unbrokenforests, being found in large clearings, openwoodland, savannas and palm groves.Although locally common, this icterid has arather patchy distribution in Argentina, and ismore evenly distributed in eastern Paraguay.Chopi Blackbirds foraged mostly on theground, and were usually found in groups of5–22 individuals. Chopi Blackbirds showedconspicuous sentinel behavior, with one ortwo individuals perching on lookouts (trees,poles or buildings) while the group foraged.As in Baywinged Cowbirds (Agelaioides badius)a descending high-pitched whistle was used asa hawk-alarm call by the sentinels (pers.observ.). Groups of Chopi Blackbirds wereoften seen mobbing and chasing avian preda-tors, even during the non-breeding season. Basic information on all the blackbirdnests can be found in Appendix 1. My nestlocations mostly agree with published reports(Azara 1802, Dalgleish 1899, de la Peña 1987,Sick 1993, Fraga 1996, Di Giacomo 2005),but the use of nests built by Rufous Horneros(Furnarius rufus) (three of the five nests foundin Corrientes) had not been reported forArgentina. Chopi Blackbirds should beincluded among the few hole nesting icterids(Orians 1985). Chopi Blackbirds sometimes breed insmall colonies in palm groves (Di Giacomo2005). None of my nests were in palm groves,and all were apparently solitary, with a mini-mal distance of 60 m between simultaneousnests (Appendix 1). Moreover, nests 1 and 9were located in isolated trees in extensive pas-tures or agricultural fields. I observed agonistic interactions betweennesting pairs and other conspecifics at four ofthe nine nests found before egg hatching. Theinteractions involved some chasing and sup-planting, with most individuals singing. Myobservations suggest that Chopi Blackbirdnests were attended by single pairs during theearlier stages of the nesting cycle. By contrast, group size in the three nestscontaining chicks ranged from five to six indi-viduals. Group members often perched in thesame branch and no intraspecific aggressionwas observed. At nest 10, only two individu-als brought food simultaneously but, becauseof the small size of the delivered prey (greencarterpillars), possibly the chicks wererecently hatched. Other three individuals usu-ally perched within 20 m of the nest withoutany visible antagonism, and on two occasionsthe five blackbirds attacked a Yellow-headedCaracara (Milvago chimachima) that flew abovethe nest tree. The five individuals observed at nest 11brought insects and spiders to the nest, and atleast three removed fecal sacs. All scolded vig-orously while I inspected the nest. The fiveindividuals also chased and mobbed CrestedCaracaras (Caracara plancus) and parasiticScreaming Cowbirds. At nest 12, at least fourof the six individuals carried insects and spi-ders to the chicks, while others scolded me, ormobbed Crested Caracaras and ScreamingCowbirds. In a previous study at the Iguazú Airportvillage, Misiones, Argentina (Fraga 1996),fledged Chopi Blackbird chicks were escortedby up to three adults, but I obtained no goodevidence of helping behavior at this stage ofthe breeding cycle. Besides, this village popu-301SHORT COMMUNICATIONSlation was subject to a high incidence ofScreaming Cowbird parasitism, and some par-asite fledglings were fed by only one adultblackbird (Fraga 1996). During a later visit tothis site (18 December 2000) I found a mini-mum of nine adult Chopi Blackbirds, but theonly fledglings I saw were five ScreamingCowbirds, escorted by one or two adult black-birds. The other adult Chopi Blackbirds in thearea were seen attacking and chasing theyoung cowbirds three times, rather than feed-ing them. One parasite chick uttered repeateddistress calls when pecked by an adult black-bird. This observation may be compared tothe few reports of host discrimination oraggression against the parasitic chicks of hon-eyguides (Short & Horne 1985) and cuckoos(Langmore et al. 2003). Screaming Cowbirdchicks do not mimic Chopi Blackbird chicksin plumage, and are conspicuously different incoloration (Fraga 1996, 1998). Chopi Black-bird fledglings have uniform blackish plum-age and bare grayish facial areas, whereasScreaming Cowbird chicks closely resemblechicks of Baywinged Cowbirds (Fraga 1998).Two of the five Screaming Cowbird chicksattacked by Chopi Blackbirds had a few blackblotches in the upperparts, the others appar-ently not (the molt sequence is described inFraga 1998). Details of the social organization of ChopiBlackbirds in the nonbreeding season (senti-nel behaviour, group mobbing) closely resem-ble those of other cooperative breeding SouthAmerican quiscalines (e.g., Orians et al. 1977,Fraga & Di Giacomo 2004). Begore egghatching single Chopi Blackbird pairs attendnests, and show agonistic behavior againstconspecifics. After egg hatching, however,other individuals (three to four) may performas helpers, bringing food and defendingnests and chicks against potential predators.Although my results are preliminary, a similarpattern occurs in cooperative breedingBaywinged Cowbirds in Argentina (Fraga1972, Orians et al. 1977, Fraga 1991). ChopiBlackbirds also resembled Baywinged Cow-birds in nesting in cavities, palm trees and thecovered nests built by other birds (Fraga1988). Most cooperative breeding icterids aremembers of the South American quiscalineclade, (Johnson & Lanyon 1999, Cadena et al.2004, Fraga 2008). Chopi Blackbirds becomeanother cooperative species in this remarkablegroup. ACKNOWLEDGMENTS. My travels in Argentina and Paraguay werefinanced by American Bird Conservancy,Asociación Guyrá Paraguay and the WorldBank. I thank all the landowners that allowme to visit their properties. My visit to theAMNH was financed by a collection studygrant from the same institution. Commentsby reviewers improved the MS. REFERENCESAzara, F. de. 1802. Apuntamientos para la historianatural de los páxaros del Paraguay y Río de laPlata. Volume 1. Imprenta de la Viuda deIbarra, Madrid, Spain. Brown, J. L. 1987. Helping and communal breedingin birds. Princeton Univ. Press, Princeton, NewJersey. Cadena, C. D., A. M. Cuervo, & S. M. Lanyon.2004. Phylogenetic relationships of the Red-bellied Grackle (Icteridae: Hypopyrrhus pyrohypo-gaster) inferred from mitochondrial DNAsequence data. Condor 106: 664–670.Dalgleish, J. J. 1889. Notes on a collection of birdsand eggs from the Republic of Paraguay. Proc.Royal Phys. Soc. Edinburgh 10: 73–88.de la Peña, M. R. 1987. Nidos y huevos de avesargentinas. Imprenta Lux, Santa Fe, Argentina.Di Giacomo, A. G. 2005. Aves de la reserva ElBagual. Pp. 201–465 in Di Giacomo, A. G., &S.F. Krapovickas (eds.). Historia natural ypaisaje de la reserva El Bagual, provincia deFormosa, Argentina. Temas de Naturaleza y302FRAGAConservación N°4, Aves Argentinas, BuenosAires, Argentina.Fraga, R. M. 1972. Cooperative breeding and a caseof successive polyandry in the Baywinged Cow-bird. Auk 89: 447–449.Fraga, R. M. 1988. Nest sites and breeding successin Molothrus badius. J. Ornithol. 129: 175–183. Fraga, R. M . 1991. The social system of a commu-nal breeder, the Bay-winged Cowbird Molothrusbadius. Ethology 89: 195–210.Fraga, R. M . 1996. Futher evidence of parasitismof Chopi Blackbirds by the specialized Scream-ing Cowbird. Condor 98: 866–867.Fraga, R. M. 1998. The interactions of the parasiticShiny and Screaming cowbirds (Molothrus bona-riensis and M. rufoaxillaris ) with a shared host,the Bay-winged Cowbird (M. badius). Pp. 173–193 in Rothstein, S. I., & S. K. Robinson (eds.).Parasitic birds and their hosts. OxfordUniv.Press, New York, New York. Fraga, R. M. 2005. Behavior, ecology and socialorganization of Saffron-cowled Blackbirds(Xanthopsar flavus). Ornitol. Neotrop. 16: 15–29.Fraga, R. M. 2008. Phylogeny and behavioral evo-lution in the family Icteridae. Ornitol. Neotrop.19 (Suppl.): 61–71. Fraga, R. M., & A. Di Giacomo. 2004. Cooperativebreeding of the Yellow-rumped Marshbird (Ict-eridae) in Argentina and Paraguay. Condor 106:671–673.Jaramillo, A., & P. Burke. 1999. New World black-birds. The Icterids. A. & C. Black Publishers,London, UK.Johnson, K. P., & S. M. Lanyon. 1999. Molecularsystematics of the grackles and allies, and theeffect of additional sequence (CYT b andND2). Auk 116:759–768.Langmore, N. E., S. Hunt, & R. M. Kilner. 2003.Escalation of a coevolutionary arms racethrough host rejection of brood parasiticyoung. Nature 422: 157–160.Orians, G. H. 1985. Blackbirds of the Americas.Univ. of Washington Press, Seattle, Washing-ton. Orians, G. H., C. E. Orians, & K. J. Orians. 1977.Helpers at the nest in some Argentine black-birds. Pp. 137–151 in Stonehouse, B., & C. Per-rins (eds.). Evolutionary ecology. Univ. ParkPress, Baltimore, Maryland.Short, L. L., & J. F. M. Horne. 1985. Behavioralnotes on the nest-parasitic Afrotropical hon-eyguides (Aves, Indicatoridae). Am. Mus.Novit. 2825: 1–46.Sick, H. 1993. Birds in Brazil. Princeton Univ.Press, Princeton, New Jersey.Accepted 27 January 2008.APPENDIX 1. A list and brief description of the Chopi Blackbird nests reported in this paper. A) Nests found from the nest building to the incubation stages. Nest 1. Estancia Mora Cué, Corrientes,  Argentina  (28o22´S,  56o08´W),  2  November 1995. Observationtime 45 min. Natural hole in dead, isolated Eucalyptus tree. Two individuals were carrying nest mate-rial into the hole.Nest 2. Estancia Rincón de las  Mercedes,  Corrientes,  Argentina  (28o19´S, 55o46´W),  24 October 2000.Observation time 90 min. Located within an old nest of Rufous Horneros (Furnarius rufus). Oneblackbird repeatedly entering the nest and probably incubating. Nest 3. Estancia La Hortensia, Corrientes, Argentina (28o26´S, 56o28´W), 20 November 2000. Observationtime 120 min. Located within an old nest of Rufous Horneros (Furnarius rufus). Two individualswere carrying nest material, and copulation was observed.303SHORT COMMUNICATIONSNests 4 and 5. Isla Yacyretá, departamento Itapúa, Paraguay (27o25´S, 56o26´W), 21 November 2001. Obser-vation time 90 min. Built in the crowns of two spiny “mbocayá” palms (Acrocomia totai), about 60 mappart. Each nest occupied by single Chopi Blackbird pairs. Nests 6 to 8. San Miguel Potrero, departamento Itapúa, Paraguay (27o04´S, 56o12´W), 22 and 23 November2001. Observation time 120 min. Three nests were built in niches at the top of three electricitypoles placed at intervals of 80 m along a power line. The cavities were shallow, and contained open-cup nests visible with binoculars. At least one nest was in the incubation stage, with one individualclosely sitting. Screaming Cowbirds visited all the nests, chased by one ot two blackbirds.Nest 9. Tobunas, Misiones province, Argentina (26o28´S, 53o53´W), 25 and 26 October 2007. Observationtime 120 min. Nest in woodpecker hole in a dead tree in a large agricultural clearing. B) Nests found with chicks. Data on helping behavior is provided in the text.  Nest 10. Rincón de Santa María, Corrientes, Argentina (27o28´S, 56o34´W), 25 October 1999. Nest found ina natural hole in a dead tree. Observation time 60 min. Nest contents could not be examined, butadults were bringing food. Nest 11. Rincón de San Mateo,  Corrientes, Argentina  (28º28´S, 55º27´W), 17 and 18  November 2000.Observation time 180 min. Nest built within an unfinished nest of Rufous Horneros, and contain-ing three unfeathered Chopi Blackbird nestlings. Nest 12. Estancia  La Golondrina,  departamento  Presidente Hayes,  Paraguay (24o59´S, 57o43´W),  25November 2001. Observation time 120 min. Nest built within the crown of a “caranday” palm(Copernicia alba), and contained two or three well-feathered Chopi Blackbird chicks.

Notas sobre la nidificación del Chopí (Gnorimopsar chopi) en Argentina y Paraguay, con datos de cría cooperativa y de parasitismo de cría por el Tordo Pico Corto (Molothrus rufoaxillaris)

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Notas sobre la nidificación del Chopí (Gnorimopsar chopi) en Argentina y Paraguay, con datos de cría cooperativa y de parasitismo de cría por el Tordo Pico Corto (Molothrus rufoaxillaris)

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