Abstract

REBOREDA, Juan C. et al. Impact of brood parasitism by Shiny Cowbirds (Molothrus bonariensis) on the reproductive success of their hosts. Hornero [online]. 2003, vol.18, n.2, pp.77-88. ISSN 0073-3407.

We present a review of the impact of brood parasitism by Shiny Cowbirds (Molothrus bonariensis) on the reproductive success of their hosts. We analysed the effect of parasitism on nest survival and on egg survival, hatching success and chick survival in successful nests. We also analysed the effect of the intensity of parasitism and egg pecking behaviour in unparasitized nests. Egg pecking produced the main impact of parasitism on host's reproductive success. This behaviour also reduced host's reproductive success in unparasitized nests. Parasitism decreased hatching success and chick survival only in hosts much smaller than the parasite. In these hosts, parasitism also increased the frequency of nest abandonment, generally as a result of the destruction of the majority of host's eggs. The cost produced by egg pecking increased with intensity of parasitism. Considering that intensity and frequency of parasitism are tightly associated, the latter would be a good predictor of the impact that Shiny Cowbird's parasitism might produce on the reproductive success of their hosts. We mention some aspects of the biology of the parasite and their hosts that we need to study in more detail to estimate the impact that brood parasitism produces on the viability of hosts' populations.

Keywords : brood parasitism; egg pecking; Molothrus bonariensis; reproductive success; Shiny Cowbird.

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