During wetland survey work at Lakelands, in Naas town, Co. KIldare I came across this unusal Rook (Corvus frugilegus). Not sure what causes the unusual colour form - and when i first saw the bird in flight I thought it was some sort of a bird of prey !
Seems the explantion below might explain the unusual colour:
Leucism, or leukism, is an abnormal plumage condition caused by a genetic mutation that prevents pigment, particularly melanin from being properly deposited on a bird’s feathers. As a result, the birds do not have the normal, classic plumage colors listed in field guides, and instead the plumage have several color changes, including:
- White patches where the bird should not have any
- Paler overall plumage that looks faint, diluted or bleached
- Overall white plumage with little or no color discernable
The degree of leucism, including the brightness of the white and the extent of pigment loss, will vary depending on the bird’s genetic makeup. Birds that show only white patches or sections of leucistic feathers – often in symmetrical patterns – are often called pied or piebald birds, while birds with fully white plumage are referred to as leucistic birds.
For more info see: http://birding.about.com/od/identifyingbirds/a/leucism.htm