Planning host exploitation through prospecting visits by parasitic cowbirds


We studied visits to potential host nests by two avian brood parasites, the host generalist shiny cowbird, Molothrus bonariensis, and the host specialist screaming cowbird, Molothrus rufoaxillaris, in the periods preceding and overlapping the laying period of their hosts. Our goal was to examine the hypothesis that during prelaying visits, cowbird females form a dynamic memory library of laying opportunities, which they deploy to target suitable nests at a later predawn period. We recorded presence of radio-tagged females within a fixed area around nests of chalked-browed mockingbirds, Mimus saturninus (a common host of shiny cowbirds), and baywings, Agelaioides badius (the main host of screaming cowbirds), using proximity data loggers placed at nests during prelaying, laying and early incubation. Our data confirmed that females of both species visit potential host nests prior to laying and that parasitic events occurred before dawn, earlier in screaming than shiny cowbirds but with little chance of host nests having been discovered on the laying day. There were interesting species differences: visits were less frequent in shiny than screaming cowbirds and the former rarely returned after laying, while screaming cowbirds visited nests repeatedly after laying and occasionally showed repeat parasitism. The higher frequency of revisiting by screaming cowbirds to baywing nests is consistent with the uncommonly long and variable baywing prelaying period, and the incidence of repeat parasitism may reflect low availability of baywing nests and greater flexibility of its parental care potential thanks to it being a social breeder.

Significance statement

Avian brood parasites synchronize their laying with that of their hosts, as this reduces egg rejection and optimizes hatching time. They also avoid parasitizing nests repeatedly, thus preventing harm to their own previously laid eggs and competition among their offspring. Further, they lay at dawn, so that location of target nests must be known from previous days’ exploration. It has been argued that these adaptations must depend on memory for the location and status of host nests within their home range, a memory feat known as ‘bookkeeping’. We study nest prospecting in a host specialist and a host generalist parasitic cowbird, using a combination of proximity radio tracking and video recordings. Our results confirm the prospecting hypothesis, report previously unknown interspecies differences and illustrate how cognitive adaptations can be studied in the context of field behavioural ecology.

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  1. Alderson GW, Gibbs HL, Sealy SG (1999) Determining the reproductive behaviour of individual brown-headed cowbirds using microsatellite DNA markers. Anim Behav 58:895–905

  2. Arlt D, Pärt T (2008) Post-breeding information gathering and breeding territory shifts in northern wheatears. J Anim Ecol 77:211–219

  3. Astié AA, Reboreda JC (2009) Shiny cowbird parasitism of a low quality host: effect of host traits on a parasite’s reproductive success. J Field Ornithol 80:224–233

  4. Banks AJ, Martin TE (2001) Host activity and the risk of nest parasitism by brown-headed cowbirds. Behav Ecol 12:31–40

  5. Bártol I, Karcza Z, Moskát C, Røskaft E, Kisbenedek T (2002) Responses of great reed warblers Acrocephalus arundinaceus to experimental brood parasitism: the effects of a cuckoo Cuculus canorus dummy and egg mimicry. J Avian Biol 33:420–425

  6. Clayton NS, Griffiths DP, Emery NJ, Dickinson A (2001) Elements of episodic-like memory in animals. Philos T Roy Soc B 356:1483–1491

  7. Clayton NS, Reboreda JC, Kacelnik A (1997) Seasonal changes of hippocampus volume in parasitic cowbirds. Behav Process 41:237–243

  8. Clotfelter ED (1998) What cues do brown-headed cowbirds use to locate red-winged blackbird host nests? Anim Behav 55:1181–1189

  9. Davies NB (2000) Cuckoos, cowbirds and other cheats. T & AD Poyser Ltd, London

  10. De Mársico MC, Gantchoff MG, Reboreda JC (2012) Host-parasite coevolution beyond the nestling stage? Mimicry of host fledglings by the specialist screaming cowbird. Proc R Soc Lond B 279:3401–3408

  11. De Mársico MC, Gloag R, Ursino CA, Reboreda JC (2013) A novel method of rejection of brood parasitic eggs reduces parasitism intensity in a cowbird host. Biol Lett 9:20130076

  12. De Mársico MC, Reboreda JC (2008) Egg-laying behavior in screaming cowbirds: why does a specialist brood parasite waste so many eggs? Condor 110:143–153

  13. De Mársico MC, Reboreda JC (2014) High frequency but low impact of brood parasitism by the specialist screaming cowbird on its primary host, the baywing. Emu 114:309–316

  14. Doligez B, Danchin E, Clobert J, Gustafsson L (1999) The use of conspecific reproductive success for breeding habitat selection in a non-colonial, hole-nesting species, the collared flycatcher. J Anim Ecol 68:1193–1206

  15. Ellison K, Sealy SG, Gibbs HL (2006) Genetic elucidation of host use by individual sympatric bronzed cowbirds (Molothrus aeneus) and brown-headed cowbirds (M. ater). Can J Zool 84:1269–1280

  16. Fiorini VD, Gloag R, Kacelnik A, Reboreda JC (2014) Strategic egg destruction by brood-parasitic cowbirds? Anim Behav 93:229–235

  17. Fiorini VD, Reboreda JC (2006) Cues used by shiny cowbirds (Molothrus bonariensis) to locate and parasitise chalk-browed mockingbird (Mimus saturninus) nests. Behav Ecol Sociobiol 60:379–385

  18. Fiorini VD, Tuero DT, Reboreda JC (2009) Shiny cowbirds synchronize parasitism with host laying and puncture host eggs according to host characteristics. Anim Behav 77:561–568

  19. Fraga RM (1998) Interactions of the parasitic screaming and shiny cowbirds (Molothrus rufoaxillaris and M. bonariensis) with a shared host, the bay-winged cowbird (M. badius). In: Rothstein SI, Robinson SK (eds) Parasitic birds and their hosts. Studies in coevolution. Oxford University Press, New York, NY, pp. 173–193

  20. Gloag R, Fiorini VD, Reboreda JC, Kacelnik A (2013) The wages of violence: mobbing by mockingbirds as a frontline defence against brood-parasitic cowbirds. Anim Behav 86:1023–1029

  21. Gloag R, Fiorini VD, Reboreda JC, Kacelnik A (2014) Shiny cowbirds share foster mothers but not true mothers in multiply parasitized mockingbird nests. Behav Ecol Sociobiol 68:681–689

  22. Guigueno MF, MacDougall-Shackleton SA, Sherry DF (2016) Sex and seasonal differences in hippocampal volume and neurogenesis in brood-parasitic brown-headed cowbirds (Molothrus ater). Dev Neurobiol. doi:10.1002/dneu.22421 published online

  23. Guigueno MF, Sealy SG (2011) Aggression towards egg-removing cowbird elicits clutch abandonment in parasitized yellow warblers, Dendroica petechia. Anim Behav 81:211–218

  24. Guigueno MF, Snow DA, MacDougall-Shackleton SA, Sherry DF (2014) Female cowbirds have more accurate spatial memory than males. Biol Lett 10:20140026

  25. Hahn DC, Sedgwick JA, Painter IS, Casna NJ (1999) A spatial and genetic analysis of cowbird host selection. Stud Avian Biol-Ser 18:204–217

  26. Honza M, Taborsky B, Taborsky M, Teuschl Y, Vogl W, Moksnes A, Røskaft E (2002) Behaviour of female common cuckoos, Cuculus canorus, in the vicinity of host nests before and during egg laying: a radiotelemetry study. Anim Behav 64:861–868

  27. Kattan GH (1997) Shiny cowbirds follow the “shotgun” strategy of brood parasitism. Anim Behav 53:647–654

  28. McLaren CM, Woolfenden BE, Gibbs HL, Sealy SG (2003) Genetic and temporal patterns of multiple parasitism by brown-headed cowbirds (Molothrus ater) on song sparrows (Melospiza melodia). Can J Zool 81:281–286

  29. Mennill DJ, Doucet SM, Ward K-AA, Maynard DF, Otis B, Burt JM (2012) A novel digital telemetry system for tracking wild animals: a field test for studying mate choice in a lekking tropical bird. Methods Ecol Evol 3:663–672

  30. Mermoz ME, Reboreda JC (1999) Egg-laying behaviour by shiny cowbirds parasitizing brown-and-yellow marshbirds. Anim Behav 58:873–882

  31. Moskát C, Barta Z, Hauber ME, Honza M (2006) High synchrony of egg laying in common cuckoos (Cuculus canorus) and their great reed warbler (Acrocephalus arundinaceus) hosts. Ethol Ecol Evol 18:159–167

  32. Peer BD (2006) Egg destruction and egg removal by avian brood parasites: adaptiveness and consequences. Auk 123:16–22

  33. Peer BD, Sealy SG (1999) Laying time of the bronzed cowbird. Wilson Bull 111:137–139

  34. Pöysä H (2006) Public information and conspecific nest parasitism in goldeneyes: targeting safe nests by parasites. Behav Ecol 17:459–465

  35. Rappole JH, Tipton AR (1991) New harness design for attachment of radio transmitters to small passerines. J Field Ornithol 62:335–337

  36. Reboreda JC, Clayton NS, Kacelnik A (1996) Species and sex differences in hippocampus size in parasitic and non-parasitic cowbirds. Neuroreport 7:505–508

  37. Rivers JW, Peer BD (2016) Relatedness constrains virulence in an obligate avian brood parasite. Ornithol Sci 15:191–201

  38. Rivers JW, Young S, Gonzalez EG, Horton B, Lock J, Fleischer RC (2012) High levels of relatedness between brown-headed cowbird (Molothrus ater) nestmates in a heavily parasitized host community. Auk 129:623–631

  39. Robertson RJ, Norman RF (1976) Behavioral defenses to brood parasitism by potential hosts of the Brown-headed cowbird. Condor 78:166–173

  40. Robertson RJ, Norman RF (1977) The function and evolution of aggressive host behavior towards the Brown-headed cowbird (Molothrus ater). Can J Zool 55:508–518

  41. Robinson SK, Robinson WD (2001) Avian nesting success in a selectively harvested north temperate deciduous forest. Conserv Biol 15:1763–1771

  42. Rothstein SI, Robinson SK (1998) Parasitic birds and their hosts: studies in coevolution. Oxford University Press, New York

  43. Rutz C, Burns ZT, James R, Ismar SMH, Burt J, Otis B, Bowen J, St Clair JJH (2012) Automated mapping of social networks in wild birds. Curr Biol 22:R669–R671

  44. Scardamaglia RC, Reboreda JC (2014) Ranging behavior of female and male shiny cowbirds and screaming cowbirds while searching for host nests. Auk 131:610–618

  45. Scott DM (1991) The time of day of egg laying by the brown-headed cowbird and other icterines. Can J Zool 69:2093–2099

  46. Seeley TD, Buhrman SC (2001) Nest-site selection in honey bees: how well do swarms implement the “best-of-N” decision rule? Behav Ecol Sociobiol 49:416–427

  47. Selonen V, Hanski IK (2010) Decision making in dispersing Siberian flying squirrels. Behav Ecol 21:219–225

  48. Sherry DF, Forbes MRL, Khurgel M, Ivy GO (1993) Females have a larger hippocampus than males in the brood-parasitic brown-headed cowbird. P Natl Acad Sci USA 90:7839–7843

  49. Smith JNM, Arcese P, McLean IG (1984) Age, experience, and enemy recognition by wild song sparrows. Behav Ecol Sociobiol 14:101–106

  50. Soler M, Pérez-Contreras T (2012) Location of suitable nests by great spotted cuckoos: an empirical and experimental study. Behav Ecol Sociobiol 66:1305–1310

  51. Soler M, Pérez-Contreras T, Soler JJ (2015) Synchronization of laying by great spotted cuckoos and recognition ability of magpies. J Avian Biol 46:608–615

  52. Spottiswoode CN, Kilner RM, Davies NB (2012) Brood parasitism. In: Royle NJ, Smiseth PT, Kölliker M (eds) The evolution of parental care. Oxford University Press, Oxford, pp. 226–243

  53. Teuschl Y, Taborsky B, Taborsky M (1998) How do cuckoos find their hosts? The role of habitat imprinting. Anim Behav 56:1425–1433

  54. Ursino CA, De Mársico MC, Sued M, Farall A, Reboreda JC (2011) Brood parasitism disproportionately increases nest provisioning and helper recruitment in a cooperatively breeding bird. Behav Ecol Sociobiol 65:2279–2286

  55. Van Nouhuys S, Ehrnsten J (2004) Wasp behavior leads to uniform parasitism of a host available only a few hours per year. Behav Ecol 15:661–665

  56. Wiley JW (1988) Host selection by the shiny cowbird. Condor 90:289–303

  57. Wyllie I (1981) The cuckoo. Batsford, London

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We thank Fundación Elsa Shaw de Pearson for allowing us to conduct this research in Reserva El Destino and Victoria Weinsztok and Cynthia Ursino for help in the field. RCS was supported by a scholarship from the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). VDF and JCR are research fellows of CONICET. This work was supported by grants from Agencia Nacional de Promoción Científica y Tecnológica and the University of Buenos Aires. All work complied with Argentinean law.

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Correspondence to Romina C. Scardamaglia.

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The study was funded by research grants of the University of Buenos Aires (W808) and Agencia Nacional de Promoción Científica y Tecnológica (PICT-2011-0045).

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The authors declare that they have no conflict of interest.

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The study was conducted with the permission of the Provincial Organism for Sustainable Development (OPDS, Buenos Aires, Argentina) and complies with the current laws of Argentina.

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Communicated by M. Soler

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Scardamaglia, R.C., Fiorini, V.D., Kacelnik, A. et al. Planning host exploitation through prospecting visits by parasitic cowbirds. Behav Ecol Sociobiol 71, 23 (2017) doi:10.1007/s00265-016-2250-8

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  • Brood parasitism
  • Molothrus bonariensis
  • Molothrus rufoaxillaris
  • Nest searching
  • Automated telemetry