HYLTON, J.H.*; BRIDGE, E.S.; GAMBLE, L.G.; SCHOECH, S.J.; University of Memphis; University of Memphis; University of Memphis; University of Memphis: Cryptic Plumage Dimorphism in Aphelocoma Scrub-Jays: Assessing Visible and Ultraviolet Reflectance Across Species and Subspecies

Recent studies of avian vision and plumage coloration have revealed a surprising degree of cryptic sexual dimorphism, with many examples of sex-based differences in UV reflectance that are invisible to humans. We examined the potential for cryptic plumage signaling in the genus Aphelocoma. This group of five scrub-jay species ranges across southern and central North America and includes cooperatively breeding species, (A. coerulescens and A. unicolor), island populations (A. insularis), tropical species (A. unicolor), and widespread species with considerable intraspecific variation in life history and appearance (A. ultramarina and A. californica). We assessed the visible and UV reflectance properties of Aphelocoma plumages using a fiber optic spectrometer to perform a series of reflectance measurements on hundreds of museum specimens representing all species within 10 subspecies groups. We then calculated quantum photon catches based on a corvid visual system to interpret the reflectance data in the context of what the birds perceive. We found subtle but potentially important differences in reflectance both between adult males and adult females and between first basic (subadult) and definitive basic (adult) plumages of some groups. Although we lack data for some subspecies groups, we have found it somewhat common for female adults to have distinctly brighter blue feathers. This characteristic appears to be most pronounced and consistent throughout the plumage in the cooperatively-breeding Florida Scrub-Jay (A. coerulescens ), which implies a relationship between sexual dichromatism and complex breeding systems.