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Brood parasitism

Behaviour and Ecology

Young cowbirds do not eject host chicks from the nest, as occurs in some avian brood parasites, but are instead raised alongside them. Cowbird chicks must therefore compete for care and provisioning with host chicks, sometimes when host chicks are much larger than themselves. We are interested in behavioural adaptations to brood parasitism in cowbird chicks, and particularly the differences in such behaviours between cowbird chicks raised in various hosts. Any such differences may arise either from developmental plasticity in cowbirds or from host-specific genotypic variation in cowbird populations. This research is relevant not only to understanding the behavioural ecology of cowbirds but more generally to understanding the influence of natal environment on behavioural development.

We are also interested in host use by South American cowbirds and the mechanisms which may determine patterns of host use. Shiny Cowbirds (Molothrus bonariensis) are host generalists, utilising numerous hosts in any one region and a total of over 200 hosts across their entire range. Screaming Cowbirds (Molothrus rufoaxillaris) are host specialists, parasitising only one host at high frequency. Why cowbirds have evolved such varying host use strategies and the mechanisms that sustain them (e.g. imprinting on hosts during chick development) are under investigation.

Fieldwork is conducted at Magdalena, about 90km from Buenos Aires, Argentina. The field site supports strong populations of both Shiny and Screaming cowbirds and also a number of their hosts.

For relevant publications on South American Cowbirds please see our collaborators Laboratorio de Ecologia y Comportamiento Animal, Prof. Juan Carlos Reboreda University of Buenos Aires, Argentina.