Yellow warbler nests, structure, building materials and cowbird parasitism

Abstract

Egg burial in Yellow Warblers is a behaviour that has been frequently observed and recorded in the ornithological literature. According to the literature, burial in North America is rarely observed in passerine species other than the Yellow Warbler. One hundred and twenty-five records of burial were found for 56 species, 89% of these records were in the context of cowbird parasitism. Most of these cases (93%) involved burial of cowbird egg(s) only. Due to the lack of host eggs being buried along with the cowbirds suggests that the majority of these burials is a result of premature egg laying by the female cowbird and the host simply buried the cowbird egg while finishing its nest. To explain the high frequency of burial observed in Yellow Warblers, Rothstein (1975) suggested that Yellow Warblers build nests with similar lining and frames. Thus, female cowbirds may not be able to determine when the nest is finished and possibly parasitize the nest too soon. The prematurely laid egg would simply be covered over by ining as the Yellow Warbler completes its nest. A total of 113 Yellow Warbler nests were dissected. (Abstract shortened by UMI.)