We found this pale specimen at Creamer's Filed Migratory Wildlife Refuge tonight. It's hard to sell from the bright snow, but the bird's neck was dark grey and not jet black.
Hi, Jim,
A variety of mutations in numerous vertebrates can cause "dilution effects" resulting in structures normally containing black or dark brown melanin being, rather, grayed or lighter brown or tan. These traits are distinguished from genetic traits involved in the various distributions of " leukism / leucism" in which there is absolute absence of the normally present dark pigment resulting in regions of pink skin or white fur, hair, or plumage. In some vertebrates, particular forms of pigment dilution may be linked to abnormal iris pigmentation, hearing abnormalities, and abnormalities in certain white blood cells.
Dave Graham, East River, SD
Discussion
1 repliesA variety of mutations in numerous vertebrates can cause "dilution effects" resulting in structures normally containing black or dark brown melanin being, rather, grayed or lighter brown or tan. These traits are distinguished from genetic traits involved in the various distributions of " leukism / leucism" in which there is absolute absence of the normally present dark pigment resulting in regions of pink skin or white fur, hair, or plumage. In some vertebrates, particular forms of pigment dilution may be linked to abnormal iris pigmentation, hearing abnormalities, and abnormalities in certain white blood cells.
Dave Graham, East River, SD