Intersexual variation in the foraging ecology of sexually monochromatic Western Wood-Pewees

Abstract

Investigators generally pool observations of males and females in studies of the foraging behavior of sexually monochromatic songbirds. However, such pooling can obscure possible intersexual differences. We compared the foraging behavior of male and female Western Wood-Pewees (Contopus sordidulus), a sexually monochromatic species, in the Sierra Nevada Mountains of California during the breeding seasons of 2007 and 2008. We recorded 143 foraging observations (male N = 74, female N = 69). Overall, mean foraging rates of females (2.8 attacks/min) were higher (P <0.001) than those of males (1.1 attacks/min). In addition, female foraging rates were significantly higher during incubation than during the nest building, nestling, and fledgling periods. When foraging, males perched higher above ground than females (means = 17.1 and 6.7 m, respectively). Differences between male and female Western Wood-Pewees in foraging rates and perch heights suggest that males may spend more time on vigilance while females focus on foraging quickly during incubation and when feeding nestlings. Because metrics such as foraging attack rates are sometimes used as indicators of habitat quality and we found that rates can differ between the sexes and among nesting stages, investigators should consider the possibility of such differences when assessing habitat quality, especially for sexually monochromatic species of birds.

Citation

Fogg, Alissa M.; George, T. Luke; Purcell, Kathryn L. 2013. Intersexual variation in the foraging ecology of sexually monochromatic Western Wood-Pewees. Journal of Field Ornithology 84(1): 40-48.