Black-Throated Blue Warblers (IMAGE) University of Chicago Medical Center Caption Male black-throated blue warblers (left) differ greatly in coloration from females (right). The opsin Sws2 appears to play a role in the evolution of these differences. Credit Mdf, DickDaniels, Wikimedia Commons Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.