Master of Science (M.S.)
Degree Granting Department
Biology (Integrative Biology)
Reed Bowman, Ph.D.
Gordon Fox, Ph.D.
Stephen Deban, Ph.D.
Aphelocoma coerulescens, scrub-jay, UV color, plumage consistency, corticosterone
Across avian systems, plumage ornamentation is often considered a signal of individual fitness, condition, sex, or status, and varies due to genetics or environmental sources. In species with structural coloration, plumage variation results from differences in the amount of energy allocated to feather growth during molt, presenting a unique opportunity to study the link between individual quality and ornamentation. In cooperative breeding species, such as the Florida Scrub-Jay (Aphelocoma coerulescens), the role of structural color as a signal is particularly important because helpers may delay breeding for one to several years and competition for space is high. Florida Scrub-Jay juveniles are sexually dimorphic in the ultraviolet range, and plumage color predicts social dominance and condition, but not adult reproductive fitness. Little is known about the consistency of ultraviolet reflectance across molts, and I tested the following questions: 1) does plumage color change across molts within individuals; 2) how do environmental variables and stress affect structural color; and 3) does adult color or change in color predict reproductive fitness?
I measured relative change in color within individuals by comparing their juvenile and first set of adult feathers after pre-basic molt. I used several measures of nutritional condition, social dynamics, habitat quality, and parasite infection to model color, and I experimentally administered corticosterone during pre-basic molt to examine the effects of increased stress on color. Plumage reflectance was compared with breeding status to investigate the role of color in breeding space acquisition.
Plumage reflectance was significantly different within individuals across molts, but juvenile and adult color were correlated. Adults were significantly less bright than juveniles, with higher proportions of UV chroma and hues shifted toward UV wavelengths. Variation in feather color was best explained by sex, mass, parasite infection, and an interaction between area of oak scrub and group size. Juvenile feather color was also strongly associated with mother ID, but this was not the case for adults even though adult color was correlated with juvenile color. Adult chroma was reduced in birds treated with corticosterone, and hues were shifted toward longer wavelengths.
No measure of adult color predicted acquisition of breeding space, but change in brightness and hue were significant predictors of acquisition for females, where breeders tended to experience greater reductions in brightness and shifts toward UV hues compared to helpers. This may be due to sex-specific differences in reproductive strategies in Florida Scrub-Jays. Females tend to disperse farther distances and breed earlier than males, potentially expending more energy foraying and searching for breeding space, which could reduce brightness if it is linked with condition. These results suggest that sexual selection is not a dominant factor in plumage ornamentation for Florida Scrub-Jays, and understanding the interaction between plumage color, personality, and reproductive fitness should be a priority for future research.
Scholar Commons Citation
Windsor, Rebecca Lynn, "Consistency of Structural Color across Molts: The Effects of Environmental Conditions and Stress on Feather Ultraviolet Reflectance" (2017). USF Tampa Graduate Theses and Dissertations.