Foraging Ontogeny in an Urban Population of Black Phoebes (Sayornis Nigricans)

The ability to forage successfully is intimately tied to juvenile survivorship in many avian species. The time it takes juveniles to develop competent foraging skills varies with the prey type and foraging behaviors. My research examined the length of time it took juvenile Black Phoebes (Sayornis nigricans), a bird species abundant in urban environments, to exhibit foraging behavior similar to adults. Black phoebes are insectivorous and forage by scanning for and then pursuing potential prey. I hypothesized that before they disperse, approximately two months after fledging, juvenile phoebes should forage as successfully as adults. Because foraging proficiency affects time allocation, the study also compared how juveniles spend their time compared to adults. In support of my hypothesis, when juveniles were five weeks old, they foraged as successfully as adults. However, by the time of dispersal juveniles did not allocate their time similarly to adults, spending more time flying and less time perched than adults. Finally, the scanning rate and duration of foraging flights were similar to adults after the second week of successful foraging (around week six of age). Overall, these results indicate that foraging is a learned behavior that juveniles develop during their first few months of independence. Early development of proficient foraging abilities increases chances of survival. However, the development of proficient foraging abilities appears to precede the development of effective time allocation, which must occur sometime after independence