Dark plumage helps birds survive on small islands

http://www.eurekalert.org/pub_releases/2015-07/copo-dph072215.php

Public Release: 22-Jul-2015
Central Ornithology Publication Office

Animal populations on islands tend to develop weird traits over time, becoming big (like Galapagos tortoises) or small (like extinct dwarf elephants) or losing the ability to fly (like the flightless parrots of New Zealand). One less-studied pattern of evolution on islands is the tendency for animal populations to develop "melanism"--that is, dark or black coloration.

•••••

Because the pattern is repeated on island after island, it is very unlikely to have developed through random chance; instead, dark coloration must provide some sort of benefit to birds on small islands. Studies in mammals and fish have found a genetic link between melanism and aggressive behavior, and Uy and Vargas-Castro speculate that the limited space available on smaller islands makes competition for breeding territories more intense, giving an advantage to the most aggressive individuals. Previous experiments with other Monarcha castaneiventris subspecies using taxidermied birds and recorded songs have shown that melanic birds react more aggressively than their chestnut-bellied counterparts when they perceive a threat to their territory.

•••••