Date of Award

Summer 7-18-2023

Degree Type

Thesis

Degree Name

Master of Science in Integrative Biology (MSIB)

Department

Biology

Committee Chair/First Advisor

Todd Pierson

Major Professor

Sarah Guindre-Parker

Second Committee Member

Joel McNeal

Abstract

Urbanization has brought grave consequences that lead to declines in many species; however, some species thrive in urban ecosystems. This allows us the opportunity to study evolution in real time, as species adapt and change in a new setting. Novel urban ecosystems have led to phenotypic divergence between urban and rural populations. There is a rich body of literature on how songbirds are affected by urbanization, however divergent signaling behaviors are less well understood. Urban color homogenization is well-documented in carotenoid-colored species. However, iridescent plumage is understudied in general, and little is understood about how environmental changes shape iridescent plumage. This study seeks to identify and explain urbanization-induced coloration differences in an iridescent species for the first time. We investigated the role of urbanization, body condition, stress, and preening effort in shaping variation in iridescent plumage coloration. We compared breeding European starlings (Sturnus vulgaris) captured across urban and rural sites to test the urban dulling hypothesis. Plumage coloration was estimated by extracting mean brightness (average area under the curve), full width half maximum (saturation; the width of the percent reflectance curve at half the maximum reflectance value), ultraviolet chroma (saturation; proportion of color in the ultraviolet range of the electromagnetic spectrum), and peak wavelength (hue; the wavelength of maximum percent reflectance) from reflectance spectrophotometry values for the throat, belly and back feathers of free-living birds. In contrast with similar studies on pigment-derived colorful species, European starlings not differ in coloration across a gradient of urbanization. We did find that body condition and preening effort both have a negative relationship with back plumage saturation, though all other plumage coloration variables were uncorrelated to preening or body condition. Since the throat plumage—the most important for courtship displays—was uncorrelated to urbanization our results do not support the idea that plumage dulling occurs in urban starlings to shape mate choice. Instead, iridescence in starlings may be a beneficial trait as this plumage type could be more resilient to the various overly abundant plumage degrading mechanisms common to cities. Future research studies should explore how exactly iridescent plumage resists urban degradation.

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