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Condition dependence of structural plumage coverage in Indigo Buntings

Posted on 25. July, 2018.

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Nuptial plumage colouration is seemingly favoured by females of avian species with regards to sexual selection. This particular secondary sexual characteristic has been previously shown to be a condition-dependent signal of individual quality among passerines with pigment-based colouration (i.e. yellows and reds). 

In contrast, relationships between structural plumage colouration (i.e. blues) and aspects of both physical quality and physiological function have been understudied. Using free-living Indigo Buntings (Passerina cyanea) as a study species, we compared the percentage of blue feather coverage to body condition, innate immune responses, antioxidant capacity, stress physiology, reproductive physiology, and parasitism. We found the overall percentage of blue feathers on individual birds to be positively correlated with testosterone levels and body condition, while negatively correlated with heterophil to lymphocyte ratio. Birds with more blue coverage were also less likely to harbour blood parasites. Our results indicate male Indigo Buntings with greater moult investment have better overall body condition, lower stress, increased testosterone levels, and decreased parasitic susceptibility

Read the full article in Avian Biology Research, Volume 11, Number 1, February 2018, pp. 54-61.


Authors: Spencer B. Hudsona,b and Travis E. Wilcoxena*
aBiology Department, Millikin University, 1184 West Main Street, Decatur, IL 62522
bDepartment of Biology, Utah State University, 5305 Old Main Hill, Logan, UT 84322

Keywords: colouration, prenuptial moult, individual quality, ecophysiology, ornithology

Image: Photographs of two Indigo Buntings (Passerina cyanea)
used in this study, demonstrating variation in blue plumage.