Non-mimetic shiny cowbird nestlings escape discrimination by baywings in absence of host nest mates

  • Juan M. Rojas RipariEmail author
  • Luciano N. Segura
  • Juan C. Reboreda
  • María C. De Mársico
Original Article


Nestlings of obligate brood parasites must obtain resources from heterospecific hosts that are attuned to the solicitation behaviours of their own progeny. Failing to match the appropriate stimuli may result in suboptimal provisioning or even the starvation of parasite young. Parasitic nestlings could overcome it by sharing the nest with host young, as long as they are able to compete efficiently for parental feedings. Here, we examined if non-mimetic shiny cowbird (Molothrus bonariensis) nestlings reared alone fail to elicit sufficient parental care from the grayish baywing (Agelaioides badius), a host that discriminates between their own and parasitic nestlings based on species-specific begging cues. We manipulated baywing broods to assess the ability of shiny cowbird nestlings to elicit parental provisioning and survive without host nest mates. Host provisioning rates and survival did not differ between shiny cowbirds reared alone and host nestlings in singleton broods. Also, growth patterns of experimental nestlings reared alone were similar to those reported for shiny cowbirds reared alongside baywing young. Hence, we did not find support for the hypothesis that non-mimetic nestlings require the assistance of host nest mates to elicit sufficient parental care from its baywing host. Furthermore, we found that shiny cowbirds that were reared alone continued receiving care from baywings after fledging, unlike shiny cowbirds from mixed broods. Our results add evidence to the idea of opposing selective pressures on the evolution of nest mate acceptance in cowbirds and suggest context-dependent host’s discrimination abilities that deserve further investigation.

Significance statement

The evolution of nest mate killing versus tolerance strategies is a long-standing question in the study of brood parasitism. Parasitic nestlings may benefit from sharing the nest with host young if they collectively induce more parental provisioning and the parasite can benefit from it. Host nest mates could also confer protection against discrimination when hosts respond preferentially to stimuli of their own kind. We examined this idea in a generalist brood parasite, the shiny cowbird (Molothrus bonariensis), and a host able to discriminate species-specific begging cues. The results showed that shiny cowbirds reared alone performed well and circumvent host discrimination also after leaving the nest. Our study supports the existence of trade-offs on the evolution of nest mate killing behaviours and adds evidence that context-dependent host’s discrimination abilities similar to those observed towards parasitic eggs can be at play towards parasitic fledglings.


Brood parasitism Nestling discrimination Coevolution Host defences Molothrus Begging 



We thank María Luisa Shaw and Luis del Soto for allowing us to conduct the fieldwork at ‘Estancia Luis Chico’ and ‘Estancia La Matilde’ respectively. We are also grateful to A. Jauregui and E. Gonzalez for assistance in the field and Manuel Soler and two anonymous reviewers for helpful comments on the manuscript.

Funding information

JMRR has a scholarship from the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). LNS, JCR, and MCDM are research fellows of CONICET. This study was supported by research grants from Agencia Nacional de Promoción Científica y Tecnológica (PICT-2014-3347 and PICT-2013-1667).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. As the experimental protocols involving the handling of birds were of minimal impact, the University of Buenos Aires committee for animal care and use did not intervene. Manipulations of baywing nests were done under permit issued by the local authority (OPDS; 303/16). Whenever possible, baywing eggs that were removed were transferred to non-experimental nests in order to minimise host reproductive losses at manipulated broods. No cowbird or host nestling was harmed or died as a result of our manipulations (see below) and we did not detect differences in predation rates between experimental and non-experimental nests.

Supplementary material

265_2019_2749_MOESM1_ESM.xlsx (20 kb)
ESM 1 (XLSX 19 kb)


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Departamento de Ecología, Genética y Evolución & IEGEBA-CONICET, Facultad de Ciencias Exactas y NaturalesUniversidad de Buenos AiresBuenos AiresArgentina
  2. 2.Sección Ornitología, División Zoología VertebradosUniversidad Nacional de La PlataBuenos AiresArgentina

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