The Physiological Effects of Bright Plumage Coloration

Abstract

Songbirds with extensive, carotenoid-based plumage tend to maintain high levels of circulating carotenoids in plasma, which could represent a potential tradeoff between maintaining brightness at the expense of carotenoid-related toxicities. To test this hypothesis, we maintained American goldfinch (Carduelis tristas) males on either a high (n=40) or a low (n=40) dose of lutein/zeaxanthan treatment for 60 days for two years during the time of molt. We took blood samples from animals before, during, and after supplementation, and analyzed the samples for aspartate amino transferase (AST) as a measure of liver and creatine kinase (CK) as a measure of muscle degradation. Additionally, we tested muscle function using a vertical ascent test, a technique that tests the performance capability of the pectoral muscles in birds. We found that AST levels were not affected. In addition, CK levels were significantly higher 60 days after the end of supplementation in animals receiving a high dose of dietary carotenoids (p = 0.008), indicating the presence of muscular degradation in these birds. Birds in the same treatment had significantly reduced flight elevations at the same time as the significant elevation in CK levels (p=0.008) at the time creatine kinase levels were elevated indicating that there was a direct effect between increased carotenoid intake, increased creatine kinase levels and outward physical ability.