Astaxanthin is the carotenoid thought to be responsible for the pink feathers we see in gulls (McGraw, Hardy 2005). I've written on this subject in a previous post, but I'm now wondering if this same carotenoid is responsible for the extra yellow/orange we see in bare parts.
Adult Ring-billed Gull. 25 March 2012. Chicago, IL. Note the pink blemish on the face, neck and breast.
Not only does this individual display pink in its plumage, but the bare parts are on hyper-orange!