Guigueno, M. F., University of Manitoba, Winnipeg, Canada,
Sealy, S. G., University of Manitoba, Winnipeg, Canada,


Several hosts of the Brown-headed Cowbird (Molothrus ater) eliminate costs of parasitism. Yellow Warblers bury cowbird eggs, possibly to clean nests, as non-egg-shaped objects have been ejected, buried, and nests deserted by other hosts. With two experiments, we tested the "nest sanitation" hypothesis by recording warblers' responses to objects similar in volume, mass, and color to cowbird eggs, and half the mass and volume, placed into nests before and during incubation. We tested whether rejection (1) declines from stars (dissimilar to eggs) through dumbbells (moderately similar) and real eggs, (2) is similar between stages, and (3) non-egg-shaped objects are ejected (least costly rejection method). Large stars were rejected (most buried) significantly more frequently (43.8%) than cowbird eggs (16.3%) before incubation, suggesting warblers reject objects unlike their own eggs to rid nests of debris. Responses to small stars and dumbbells, and foreign warbler eggs, were similar in both stages. Stars were rejected (most ejected or selectively buried) more frequently (28.8%) than dumbbells (1.3%) and warbler eggs (0%). Burial may keep nests clean, with cowbird eggs rejected in the process.

Oral presentation

Session #:G03
Date: Tuesday, 8/5/08
Time: 2:15 PM

Presentation is given by student: Yes