Sex-specific environmental sensitivity is transient in nestling Tree Swallows (Tachycineta bicolor)

Abstract

Studies investigating how male and female offspring respond to poor environmental conditions have often focused on species in which members of one sex are considerably larger than the other. We studied the impact of reduced maternal provisioning on post-natal development in nestling Tree Swallows (Tachycineta bicolor), a species displaying slight-to-moderate sexual size dimorphism. We reduced maternal provisioning via maternal feather clipping, and studied the effects on growth rate, immune function, and corticosterone (CORT) levels of male and female nestlings. Nestlings of clipped mothers were lighter at hatch than nestlings of control mothers. There was also a trend for male nestlings of clipped mothers to be lighter at hatch than female nestlings, a pattern not detected in control nests, suggesting possible sex-specific embryonic sensitivity. Although female nestlings grew more slowly than male nestlings when faced with poor environmental conditions, this was only detected for the first few days post-hatch. Maternal feather clipping had no sex-specific effect on nestling CORT levels, or immune function. Interestingly, nestlings raised by feather-clipped mothers had a stronger immune response to a phytohaemagglutinin challenge than nestlings raised by control mothers. We conclude that Tree Swallows show sex-specific sensitivity to reduced environmental quality, but only during the early post-natal growth period.