Food availability, growth, and heritability of body size in nestling tree swallows (Tachycineta bicolor)

Abstract

I studied the effects of food deprivation on the growth, final size, and inheritance of body size in nestling tree swallows (Tachycineta bicolor). Each experimental brood was divided into deprived and fed nestlings. Deprived nestlings showed relatively poor growth during the experimental stage (days 5–8), but were not significantly different in size from either their nestmates or control young at day 16. Parents of experimental broods did not compensate by increasing their food delivery rate. Heritability estimates of tarsus length were similar for deprived and fed nestlings. For control nestlings, tarsus length was significantly heritable at days 9 and 16, and bill length was heritable at day 16. There were no significant heritability estimates for wing length or body mass. Small sample sizes and single-parent–offspring regression likely inflated the standard errors associated with the heritability estimates. The mechanism that allowed deprived nestlings to grow as large as control and fed nestlings remains unknown.