Arnaud A.

Arzel C.

Elmberg J.

Fritz H.

Guillemain M.

Legagneux P.

Lepley M.

Massez G

Pin C.

Journal of Ornithology

English

UTUPub

SHORT NOTERisky foraging leads to cost-free mate guarding in male tealAnas creccaMatthieu Guillemain Æ Céline Arzel Æ Pierre Legagneux Æ Johan Elmberg ÆHervé Fritz Æ Michel Lepley Æ Christophe Pin Æ Antoine Arnaud ÆGrégoire MassezReceived: 11 July 2006 / Revised: 20 October 2006 / Accepted: 21 October 2006 / Published online: 12 December 2006 Dt. Ornithologen-Gesellschaft e.V. 2006Abstract Mate guarding by males is common in spe-cies with long-lasting pair bonds. We tested if the needto guard females affected foraging depth in male teal(Anas crecca), and if they were more vigilant than fe-males when foraging with submerged eyes (preventingmonitoring of competing males and predators). Thesepredictions were not supported, suggesting that forag-ing depth selection is primarily driven by other factors,presumably food related. A likely reason why deeplyforaging males did not increase vigilance is that 37.5%of the foraging time was already dedicated to it. Theapparent lack of guarding costs in foraging male tealmay explain why such small ducks can maintain pairbonds for up to 7 months.Keywords Circumannual  Foraging behaviour Mate guarding  Teal  VigilanceIntroductionMany bird species form annual pair bonds long beforenesting (e.g., Black 1996). Mate guarding by males is acommon phenomenon in these species. This may affectdaily time budgets for up to 7 or 8 months per year(e.g., Paulus 1983), not to mention species with lifelongmonogamy, in which males may have to guard theirmate throughout life (e.g. geese; Black et al. 1996).Consequently, mate guarding may have positive effectson fitness in both sexes in terms of natural as well assexual selection. For males, this is often seen as a trade-off between vigilance, which reduces foraging effi-ciency, and enhanced breeding success, by sustainingthe pair bond and preventing extra-pair copulations(e.g., Birkhead and Parker 1997).Pairing in fall or early winter is considered to beadaptive in dabbling ducks Anas spp. (Hepp and Hair1983), as mated birds get a dominant status withinflocks that confers better access to food (e.g., Hepp1986; Black 2005). This in turn allows paired females toimprove body condition earlier than unpaired birds,which is likely to later translate into higher breedingsuccess (due to the negative relationship betweenbreeding date and success in Anatidae; Bowler 2005;Elmberg et al. 2005). However, precocial pairing alsohas drawbacks, especially for males; due to male-Communicated by F. Bairlein.M. Guillemain (&)  C. ArzelOffice National de la Chasse et de la Faune Sauvage,CNERA Avifaune Migratrice , La Tour du Valat,Le Sambuc, 13200 Arles, Francee-mail: m.guillemain@oncfs.gouv.frC. Arzel  J. ElmbergDepartment of Mathematics and Natural Sciences,Kristianstad University, 291 88 Kristianstad, SwedenC. ArzelLaboratoire d’Ecologie des Hydrosystèmes,Université Paul Sabatier, 118 route de Narbonne,31062 Toulouse, FranceP. Legagneux  H. FritzCentre d’Etudes Biologiques de Chizé,CNRS UPR 1934, 79360 Beauvoir sur Niort, FranceM. Lepley  C. Pin  A. ArnaudStation Biologique de la Tour du Valat,Le Sambuc, 13200 Arles, FranceG. MassezLes Marais du Vigueirat, Mas Thibert,13200 Arles, France123J Ornithol (2007) 148:251–254DOI 10.1007/s10336-006-0120-2biased sex-ratios in duck populations (Baldassarre andBolen 1994), males have to devote much time toguarding their female (e.g., Davis 2002; Guillemainet al. 2003). Male vigilance thus offers the female saferefficient foraging conditions, but is costly to males, ifnothing else through reduced foraging efficiency.In an earlier flyway-level study (Guillemain et al.2006, in press), we observed that teal (Anas crecca)gradually increase foraging depth from September toAugust. This change is apparently due to predation riskrestricting the behavioural repertoire in winter to safershallow feeding methods, i.e., those with the eyes abovethe water surface (see also Guillemain et al. 2001).Conversely, the lower frequency of fly-overs by poten-tial predators as the annual cycle progresses allows tealto use a wider variety of methods, including riskierdeeper foraging when prey availability and energyrequirements make it necessary. However, deep forag-ing with the eyes submerged not only limits the ability todetect predators, for a male it also prevents monitoringother males. Given (1) the costs of mate guarding, (2)that teal are paired for several months before breeding(e.g. Johnson and Rohwer 1998), and (3) the theoreti-cally high relative energy requirements due to smallbody size compared to other dabbling ducks (ca. 300 gon average), we hypothesized that there should beintersexual differences in teal foraging behaviour.Our aims were: (1) to determine if both sexes switchto deeper foraging methods over the annual cycle and,if so, if they do it at the same rate; alternatively, malesmay maintain vigilance by foraging shallower, e.g. byfeeding on different food types than females, and (2) totest whether males and females partition foraging timeinto feeding bouts and interruptions in the same waywhen they rely on deep foraging. As deep foragingprevents monitoring of competing males, we hypothe-sized that deep foraging males should have shorterfeeding bouts and/or longer foraging interruptions.Study sites and methods are described in detail inGuillemain et al. (2006, in press). In brief, we usedfocal individual observations (Altman 1974) of forag-ing teal, chosen at random within flocks during daylighthours at 25 different sites in seven geographical areaswithin its flyway in western Europe (from Camargue insouthern France to Västerbotten in north-centralSweden), covering the whole annual cycle except au-tumn migration stopovers. In total, 658 focal observa-tions, i.e., the duration of ten successive foraging boutsusing the same foraging method, plus the duration ofthe ten associated foraging interruptions, were re-corded (244 females and 414 males). For each bird, wecalculated an average value of bout length for foragingas well as for interruptions. Each foraging posture wasassociated with a feeding depth based on body mea-surements in Thomas (1982), e.g., bill length for dab-bling, head + neck length for dipping, etc. Foragingdepth does not necessarily depend on the depth oflakes, since ducks may also seek floating seeds andinvertebrates in the water column. High turnover ratesin teal assemblages (Pradel et al. 1997) made doublerecording of the same individual unlikely, with thepossible exception of breeding lakes where density islow. Because each focal individual relied on one for-aging method, associated with a certain depth, hence adiscontinuous variable, means of behavioural parame-ters were computed for all birds per 10-day period(foraging depth and duration of foraging and inter-ruption bouts).We have earlier demonstrated that increased use ofdeep foraging methods from September to August isassociated with a relaxation of predation risk (Guille-main et al. 2006, in press). Here, we do not address whybirds change behavior, but rather use ANCOVAs tocompare sex-specific patterns of mean foraging depthand duration of feeding bouts and interruptions overthe year.The model exploring mean foraging depth in rela-tion to date and sex was significant (F3.55 = 7.49,r2 = 0.29, P = 0.0003). However, neither sex nor sex ·date had a significant effect (sex: F = 0.03, P = 0.8539;sex · date: F = 0.08, P = 0.7792). Instead, all variancewas explained by date, i.e. foraging depth increasedseasonally (10-day periods: F = 21.37, P < 0.0001;Fig. 1) at the same rate in both sexes, which on averageforaged at the same depth.For individuals foraging with submerged eyes, themodel including sex, date, and sex · date did not fitwith variation in average length of feeding boutsFig. 1 Annual variation in foraging depth of male (dots) andfemale (circles) teal (Anas crecca) (mean ± SE), expressed per10-day period starting 1–10 September. The main phases of theannual cycle are indicated under the x-axis. See main text forstatistics252 J Ornithol (2007) 148:251–254123(F3.52 = 0.36, r2 = 0.02, P = 0.7848), nor feeding inter-ruptions (F3.52 = 1.35, r2 = 0.07, P = 0.2682). The par-titioning of behaviour into foraging and vigilance thusremained unchanged over time, and did not differ be-tween sexes when foraging in a posture preventingvigilance. Deep foraging bouts lasted 1.88 s on average(±0.09 SE, n = 56), feeding interruptions lasted 1.20 s(±0.06 SE, n = 56).Among dabbling ducks, mate guarding has beenshown to strongly influence male behavior in wigeon(A. penelope) (Mayhew 1987; Guillemain et al. 2003)and gadwall (A. strepera) (Dwyer 1975). Deeply for-aging male teal cannot detect competing males, which iswhy we hypothesized that they should use this behav-iour less than females do. However, this is not what weobserved. Both sexes had similar foraging depths, andswitched from shallow to deep foraging at the same rateover time. In a previous study, we hypothesized thatrelaxing predation risk over time would allow teal ingeneral to increase foraging depth in response to higherenergy requirements and/or changing food availability(Guillemain et al. 2006, in press). The latter factors maythus be more important than intrasexual competition toforaging depth selection in males or, alternatively, deepforaging is not as costly as hitherto assumed in terms ofdecreased ability to monitor competing males.Our second prediction, i.e. that deeply foragingmales unlike females alter their partitioning ofbehaviors by increasing vigilance, was not supportedeither. Average foraging bout length was similar (<2 s)between sexes, and interruptions lasted 1.2 s in bothmales and females. We suggest that deeply foragingmales already have such high anti-predator vigilance(in terms of frequency of bouts as well as proportion oftime) that they do not have to increase it further toguard their mate. As a comparison, male wigeon in-creased vigilance from 3.32 to 14.36% of foraging timeafter they paired (Guillemain et al. 2003). The corre-sponding percentage here is 37.5% for deeply foragingteal. This implies that, as opposed to earlier studiesdocumenting high costs of mate-guarding, male teal donot pay a significant price for guarding their mate, atleast when foraging. This may explain how such rela-tively small birds, with high relative energy require-ments, can afford to form and defend pairs for up to7 months a year (Johnson and Rohwer 1998).ZusammenfassungRiskante Nahrungssuche erlaubt männlichen Kricken-ten Anas crecca ein kostenfreies BewacherverhaltenBei Arten mit langer Paarbindung findet man beiden Männchen häufig ein Bewacherverhalten. Wirhaben untersucht, ob die Notwendigkeit, die Weibchenzu bewachen männliche Krickenten (Anas crecca) inder Intensität der Nahrungsaufnahme beeinträchtigte,und ob sie bei der Nahrungssuche mit den Augen unterWasser wachsamer waren als die Weibchen (um einerÜberwachung konkurrierender Mänchen und Präda-toren vorzubeugen). Diese Hypothesen bestätigtensich nicht, was nahelegt, dass der Selektionsdruck aufdie Intensität bei der Nahrungssuche primär von and-eren, vermutlich an die Nahrung gekoppelten Faktorenangetrieben wird. Ein Grund, wieso intensiv nachNahrung suchende Männchen ihre Wachsamkeit nichterhöhten, liegt wahrscheinlich darin, dass 37.5% derZeit auf Nahrungssuche bereits auf Wachsamkeits-verhalten verwendet wurde. Dass es bei Kricken-tenmännchen anscheinend keine Bewachungskostengibt, könnte erklären, wieso diese kleine Entenart einebis zu sieben monatige Paarbindung aufrecht erhaltenkann.Acknowledgments We are most grateful to the managers of thestudy sites, especially the Marais du Vigueirat for the Camargue,the Ligue pour la Protection des Oiseaux and the FédérationDépartementale des Chasseurs (FDC) de Charente-Maritime forthe Atlantic sites, the Réserve Naturelle de Chérine and theFDC de l’Indre for the Brenne lakes, the FDC de l’Eure and R.Legay for the Grand’Mare reserve and hunting ponds, and thecounty administration of Västerbotten for permission to workwithin the Brånsjön reserve. The staff at the Biosphere Reserve‘Kristianstads Vattenrike’ is acknowledged for valuable help incoordinating landowner contacts. We also thank those whohelped in the field, especially N. Guillon, F. Latraube and L.Tison, and two referees for their comments on an earlier versionof the manuscript. M. Guillemain received a doctoral grant fromthe Conseil Général Poitou-Charentes when working at theAtlantic sites. C. Arzel was supported by a PhD Grant fromONCFS and grants V-124-01 and V-98-04 from the SwedishEnvironmental Protection Agency. P. Legagneux received agrant from the university Louis Pasteur of Strasbourg, France.ReferencesAltman J (1974) Observational study of behaviour: samplingmethods. Behaviour 49:227–267Baldassarre GA, Bolen EG (1994) Waterfowl ecology andmanagement. Wiley, New YorkBirkhead TR, Parker GA (1997) Sperm competition and matingsystems. In: Krebs JR, Davies NB (eds) Behaviouralecology—an evolutionary approach. Blackwell, Oxford, pp121–145Black JM (1996) Introduction: pair bonds and partnerships. In:Black JM (ed) Partnerships in birds –the study of monog-amy. Oxford University Press, Oxford, pp 3–20Black JM (2005) Ecology of social behaviour. In: Kear J (ed)Ducks, geese and swans. 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Risky foraging leads to cost-free mate guarding in male teal Anas crecca

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Risky foraging leads to cost-free mate guarding in male teal Anas crecca

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