Last week I photographed some Black-billed Magpies on Antelope Island State Park and one of them was partially leucistic which means it was showing white feathers where they should have been a different color, in this case the feathers should have been black. When the magpie landed on a budding greasewood bush two white secondaries were exposed on the underside of the bird’s right wing sandwiched in between normal colored feathers.
This image shows the underside of a normal Black-billed Magpie. Note that where the partially leucistic has the two white feathers this bird has black feathers.
Leucism (occasionally spelled leukism) is a general term for the phenotype resulting from defects in pigment cell differentiation and/or migration from the neural crest to skin, hair, or feathers during development. This results in either the entire surface (if all pigment cells fail to develop) or patches of body surface (if only a subset are defective) having a lack of cells capable of making pigment.
This image shows the partially leucistic magpie lifting off and shows that the lack of pigmentation of those two secondary feathers from a dorsal view. This magpie may have additional feathers on it’s left wing lacking pigmentation because I can see a white feather behind the bird’s dangling feet but I don’t have any clear images of the bird’s left side to be sure if it has more than one white feather on that side.
This image shows a dorsal view of a normal colored Black-billed Magpie.
You could say that the partially leucistic Black-billed Magpie is “pied” or has a “piebald” effect. And who knows, if this partially leucistic Black-billed Magpie has a successful nesting season we might be seeing more partially leucistic Black-billed Magpies on the island.
Life is good.