Archive for January 7th, 2010

Among the winter visitors to our area are Snow Buntings (Plectrophenax nivalis). I most often see flocks of them along the roadside, where they flush and fly up together in a drift of wings as your car approaches. Recently, there was a flock of them in the soybean field neighbouring our property. When I went out to look at them, they flew up into the top of a maple tree, where they sat chattering amongst themselves. Loquacious birds, they carry on a stream of commentary.

Snow buntings are about 6 inches, or 15 cm long. They breed on the rocky tundra, far north. Nests are tucked into crevices and cavities amongst the rocks. The nest is loosely built with grass, moss, lichen, roots and leaves, and is lined with plant down, feathers and fur. Snow buntings eat a diet of insects and grass and weed seed, although young are fed a diet that is 100% insects.

When food becomes scarce, they move to their wintering grounds across central North America, where they forage in sometimes very large flocks, in snow-covered fields. Flocks may include a few Lapland Longspurs (Calcarius lapponicus) or Horned Larks (Eremophila alpestris).

As spring approaches, the males will return to the north 4 to 6 weeks before the females, establishing themselves on territories. Once the females arrive and choose a mate, nesting begins. It has been found that the number of eggs birds lay, or clutch size, shows latitudinal variation. That is, birds of the same species, nesting farther north tend to have larger clutches than those nesting farther south.

Ornithologist N.P. Ashmole examined this phenomenon and concluded that latitudinal variation in clutch size is related to the increase in resource abundance. That is, in areas where food suddenly becomes abundant, as it does in the north when mosquito season arrives, birds have larger clutches of eggs than do those of the same species nesting in areas where resources are more stable over the year. Ashmole’s hypothesis has been confirmed by other ornithologists studying clutch size. You can read more about variations in clutch size at this Stanford site.

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