Saturday, February 05, 2011

White-throated sparrows

Now that we have 20 inches of snow on the ground, the juncos and white-throated sparrows are able to reach the high seeds on the asters. Both species arrived in my backyard back in November, scratching around the brushpile, plucking seeds off some of the grasses. White-throated sparrows and juncos are among Missouri's more common wintering birds; they migrate from the rapidly disappearing boreal forests of Canada to fan out all over North America. Some white-throated sparrows fly all the way to the Amazon, making the route the longest of all migratory songbird routes. Our Christmas Bird Count participants logged 850 white-throated sparrows and 2066 juncos. Plenty of native seeds to go around for both species in my area, and while during the winter the sparrows forage for seeds and nuts on the ground, in spring and summer they live primarily on arthropods and spiders.

White-throated sparrows are the most abundant songbird in the boreal and the northern Great Lakes. 85% of their population nests in northern Ontario and Quebec, and the rest spend their breeding season in southwestern Yukon and the northern Great Lakes region. Their breeding biology is curious: there are two color morphs of the white-throated sparrow, one with tan markings on the head and the other with more noticeable white and black marks. As monogamous breeders, each pair consists of one tan striped and one white striped bird. The mixed pairs produce equal numbers of each color morph. According to the Boreal Songbird Initiative, there's a good reason for the mixed pairing:
"White striped males are more aggressive and territorial and less faithful than the tan striped males. Tan striped females provide more parental care than white striped females....Uniform pairs are deficient in either territoriality or parental care."

96% of pairs are therefore mixed.

The Canadian boreal forests contain 25% of all remaining forests on Earth. 80% of the forest remains intact, but is threatened by logging and oil exploration. The United States is the leading importer of boreal forest products; 2/3 of all the wood cut in the boreal is used to make paper products like catalogs and junkmail in America. Large retailers such as Home Depot will not sell products from the boreal, but other retailers aren't as conscientious. The destruction of the boreal directly impacts the white-throated sparrow populations, not to mention other songbird, mammal and countless other life forms that live there. White-throated sparrows are declining in the eastern side of its range, where the clearcut areas are reverting to second growth forest. Young, new forests lack the structural features and composition required for forest-dwelling songbirds to breed. The white-throated sparrow population is holding steady in the western reaches of their range due to minimal forest disturbance factors which cause periodic breaks in the canopy, encouraging rich understory production. The sparrow's wintering grounds are healthier than some parts of their breeding grounds and have been declared "sufficient." Backyard bird feeders, while not vital for their sustainability, certainly don't hurt populations.

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