Who is Missing?
Oct 29, 2018
From late summer through fall, bird species in our yards and woodlands begin to disappear. Bright colors are replaced by subdued elegance, and as our summer birds begin to head south, the year-round residents begin to establish winter-feeding territories, showing up in our yards in growing flocks of chickadees, titmice, nuthatches , many woodpeckers and finches.
So who heads south? Largely it is the birds that depend primarily on insects and flowers for food. Hummingbirds begin to head out in August and September, well before the last flowers disappear from our gardens. In a few parts of the extreme southern and western United States they will stay the winter (or in the case of Rufous Hummingbirds, more in for the winter), but most of the country is too cold to support these little bundles of energy. Orioles also go south before the coming winter months. Although these larger birds could probably adapt to winter in some parts of the country, there simply is not enough food (fruit, nectar and insects) for them to survive.
Most warblers, of course, leave North America as their supply of creeping and crawling things declines for the year. A few will stay in the southern parts of the country, and one, the Yellow-rumped Warbler, has adapted so it can feed on the waxy berries of the wax myrtle, bayberry and juniper in the winter., allowing it to stay at lower elevations of the country (excluding parts of the Northwest and much of the Great Plains). Flycatchers and swallows are out of here for obvious reasons – flying insects are at a premium in the colder, wetter weather of winter.
For a whole bunch of other birds, fall migration is variable. Some, like Blue Jays, head south in larger or smaller numbers, staying pretty much within their range, but shifting around and spreading out to make better use of reduced food supplies. Banding research seems to indicate that others, like the Robins, may withdraw completely from the northernmost parts of their range, hopscotching over some of their more sedentary kin to winter in the southern states.
And some, like goldfinches, are simply wanderers, moving around within their range in response to food availability, weather conditions and, perhaps, pure whim - which reason do you prefer!?