Sunday, July 18, 2010

House Sparrow

Digital photography has revolutionized my birding. I am excited even to take a picture of the lowly House (or English) Sparrow. They are despised and ignored by most birders and banders. Not only have these sparrows been introduced from England and Germany, they are ubiquitous (they have a nearly world-wide distribution) and take over nesting cavities of native species. Why were they introduced? I read that people wanted every bird mentioned in Shakespeare (or maybe birds of the Bible) to inhabit Central Park. In any case, the English tend to introduce British birds around the world.

House Sparrows prove to be interesting. The species demonstrates evolution at work. Since their introduction to Brooklyn in 1851 (and San Francisco in 1871, and Salt Lake City in 1873), House Sparrows have evolved! Today House Sparrows are smaller in the southern parts of North America and larger in the north. Furthermore, they have longer limbs in warm climates and shorter ones in cooler areas. (Similar size trends are noted for many species. Larger birds retain heat better than smaller ones since the larger ones have less of a surface to body mass ratio. And you would want shorter legs in cool climates to protect you from heat loss.)

Lowther and Cink (2006) also cite an 1898 study of House Sparrows after a Rhode Island ice-storm. Half of the 136 birds brought in to a lab died. Larger males survived more often than smaller ones. Females showed different survival patterns--average-sized females survived better than larger or smaller ones. This study is a clasic example of natural selection.

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