You never know when a natural wonder might wander into your awareness. While I was washing dishes at the kitchen sink, movement outside the window caught my attention. There on the ground was a …
You never know when a natural wonder might wander into your awareness. While I was washing dishes at the kitchen sink, movement outside the window caught my attention. There on the ground was a beautiful mottled bird kicking through the leaf litter with great vigor in search of insects and seeds.
That behavior, along with the rounded head, stocky legs and pale yellowish bill tinged toward dark gray on the upper mandible, suggested that my visitor was a fox sparrow. Parts of the bird’s coloration confirmed that too—the deep cinnamon brown of the tail and wings, as well as streaks of rust and gray on the head.
But something about the bird’s upper body coloration didn’t match up. There were irregular patches of white spattered among the rich russet feathers.
Such abnormal plumage patterns point to leucism. According to the Cornell Lab of Ornithology, “leucism is not a genetic mutation, but rather describes defects in pigment cells that are caused during development. This may result in full leucism, where there is a reduction in all types of pigment. An animal with full leucism will appear paler than normal.”
In the case of my backyard bird and its splotchy patches of white, the energetic little sparrow was likely displaying partial leucism in a pattern referred to as “pied” or “piebald.”
Leucism differs from albinism, which results from a genetic mutation that interferes with production of the pigment melanin. Albinism causes a lack of pigmentation in all body parts, not just feathers. As opposed to eye color in albinism, the eye color of leucistic animals is not affected, and will appear normal.
To see images of fox sparrows in their typical coloration, visit the Cornell Lab of Ornithology’s Macaulay Library at search.macaulaylibrary.org/catalog?taxonCode=foxspa&mediaType=photo&sort=rating_rank_desc.
Learn more about this species at www.allaboutbirds.org/guide/Fox_Sparrow/overview.
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