RELATIONSHIP OF AGE AND SEX TO SIZE AND COLOR OF EASTERN PHOEBES

We recorded variation in body size and ventral plumage coloration in a population of individually marked Eastern Phoebes (Sayornis phoebe). The venter of Eastern Phoebes is mostly gray with gray mottling on the breast. Most birds have a white bib which, although usually small, ma y cover much of the breast and abdomen. We found no significant differ ence in percentage gray area between males and females, but after-seco nd-year (ASY) birds had significantly less gray on their breasts than second-year (SY) birds. Males had significantly longer mean wing lengt hs, tarsal lengths, and vent-tail lengths than females. There was cons iderable overlap of wing, tarsal, and vent-tail lengths between the se xes, but the size differences held both overall and separately in SY a nd ASY birds. We generated a discriminant function which correctly cla ssified 79% (39/49) of females and 95% (22/23) of males. Despite their similar appearance, male Eastern Phoebes are larger than females, at least in the parameters we measured.