Abstract
Plumage ornamentation is often considered a signal of fitness, condition, sex, or social status. This theory holds for species with structural UV color, which is influenced by a variety of factors such as environmental pressures during molt or heritability. However, little is known about the consistency of ornamentation and signaling across time in individuals with structural color. We compared juvenile and adult feathers in free-living Florida Scrub-Jays (Aphelocoma coerulescens) to measure UV color change within individuals across molts and to assess possible sources of change. We used multiple imputation to estimate missing data and a combination of pooled estimates and model averaging to infer which parameters explain observed variation in UV color. We also tested whether adult color or relative color change from juvenile to adult plumage predicted acquisition of breeding space. UV color was not consistent across annual molts, as adult feathers reflected significantly less light but greater proportions of UV light than juvenile feathers. Juvenile color was most affected by quality of natal environment and maternal effects whereas adult color was influenced by condition and juvenile color. Adults dosed with corticosterone produced feathers with less UV ornamentation compared to control adults. Feather color did not predict acquisition of breeding space in adults, but females that experienced reductions in UV color across molts were more likely to obtain breeding space, which may reflect sex-specific differences in reproductive strategies in Florida Scrub-Jays. Our evidence suggests that structural color acts as a signal of sex, age, and condition; but ornamentation is only weakly related to acquisition of breeding space and thus unlikely to be under strong sexual selection. Ornamentation may just be one factor among many, such as personality, social dominance, or position in social networks, that determine how jays interact and compete for breeding space.
Consistency of structural color across molts: The effects of environmental conditions and stress on feather ultraviolet reflectance