Red is the color of passion, even for birds. A new study led by the University of Colorado shows that testosterone of male North American barn swallows intensely increased when researchers artificially darkened their breast feathers to a deep red that is known to be most attractive to the female birds. The birds likely had more testosterone pumping through their bodies because of amorous interactions with the opposite sex and more run-ins with jealous males, said CU assistant professor Rebecca Safran, lead author of the study. The jump in testosterone was unexpected because it was observed at the time in the breeding cycle when levels of sex steroids are typically declining, Safran said. "Males that are darker have greater evolutionary fitness," she said. The experiment has a significant impact on evolutionary studies: It shows that a simple appearance alteration -- a minor bird makeover -- triggered physiological changes. Kevin McGraw, a co-author of the study from Arizona State University's School of Life Sciences, said the results indicate that a bird's hormonal profile is influenced by its outward appearance. A paper on the subject will be published in today's issue of "Current Biology." Other co-authors include James Adelman and Michaela Hau, of Princeton University. The two-year study was funded primarily by the National Science Foundation. Click here for the full article.
