Partial Leucistic Eurasian Tree Sparrow

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.