Yesterday at Malibu Lagoon, we saw a group of Pelicans preening themselves. We saw saw of them rubbing heir heads on their backs. This turns out to be an instance of cosmetic coloration in birds. During mating season, they make their heads yellower by applying oil from the uropygial gland. This article I found discusses cosmetic coloration at length: http://orn.mpg.de/documents/kempenaers/Kemp_66.pdf
Here are a couple of beautiful close-up shots of Pelicans engaging in this activity taken by Vivek Vatsyayan:
