An Odd Pair: Social Monogamy in an Avian Brood Parasite

ROMINA C. SCARDAMAGLIA; ALEX KACELNIK; JUAN C. REBOREDA

Minneapolis, Minnesota

Congreso; International Society for Behavioral Ecology 2018 Conference; 2018

University of Minnesota

Social monogamy predominates in avian mating systems, but this strategy seems unlikely among brood parasites, since hypotheses regarding avian mating systems predict that the absence of parental care should lead to an increase in numbers of mates for both sexes. The screaming cowbird (Molothrus rufoaxillaris) is an extreme host-specialist brood parasite. It has been suggested that they are socially monogamous because they travel in pairs throughout the day. However, the extent of social monogamy in this species and its potential benefits remain unknown. Hypotheses for monogamy in cowbirds suggest males may provide females with services such as aid in nest-searching and relocation, and access to nests by distracting hosts. Alternatively, social monogamy may be the product of mate-guarding by males to defend exclusive access to a female. We radio-tracked pairs of screaming cowbirds to collect data on spatial behavior and social mating system. Monogamous pair bonds endured throughout the entire breeding season, with males and females remaining associated during the day and the night. Interestingly, this mating strategy resulted markedly different from the social polygyny/promiscuity shown by host generalist shiny cowbird (M. bonariensis), a closely related species, suggesting that these contrasting mating systems may respond to differences in host-use specialization.