Summary
Avian brood parasites usually severely depress the reproductive success of their hosts, yet many host species, including those presumably capable of ejecting parasitic eggs, accept them. Female, brood-parasitic, Brown-headed Cowbirds typically remove a host egg when they lay their own and damage some host eggs in the process of ejecting a host egg. Data from a field study of Red-winged Blackbirds show that these costs, which cannot be avoided by ejecting the parasitic egg, account for some of the reproductive losses attributable to parasitism, but part is due to the presence of the cowbird egg in the nest. To assess whether ejection would be favoured under current circumstances, the probable damage a female Redwing could cause to her own eggs by attempting to eject a cowbird egg needs to be determined.
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Røskaft, E., Orians, G.H. & Beletsky, L.D. Why do Red-winged Blackbrids accept eggs of Brown-headed Cowbirds?. Evol Ecol 4, 35–42 (1990). https://doi.org/10.1007/BF02270713
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DOI: https://doi.org/10.1007/BF02270713