Seasonal Changes in Bird Territoriality

During the breeding season most birds defend their territories with song and visual display. Watch your feeder as spring approaches. Gradually the social pattern of the birds using will change. Birds that had been feeding in flocks, such as chickadees and White-throated Sparrows. begin appearing more and more as pairs or solitary birds. They may burst unexpectedly into song or fly off pell-mell hurriedly dashing after some real or imagined violation of their territorial sovereignty.

Just the opposite occurs in late summer. Species that had shown no signs of sociability begin to gather into flocks. In part this is due to newly flying young that move around in small groups. These groups coalesce, adults join them, and they grow into large flocks. By early fall, flocks of blackbirds, grackles, starlings, robins, or swallows may number in the hundreds or thousands, The chickadees once again begin to move in small foraging groups. White-throated Sparrows stop their singing and join small flocks.

Flocking in the winter has the advantage of making birds less vulnerable to predators and can also make finding food a little easier; when one flock member finds a good feeding site, the others join in.

Black-capped, Carolina, and Chestnut-backed Chickadees are good examples of birds with seasonal changes in spacing behavior that you can easily witness in your own backyard. During the breeding season these three species are highly territorial. Pity the individual bird who wanders into a neighbors' area -- the greeting will be the entire belligerence a tiny bird can muster. In the fall, however, the local birds that were so intolerant of one another in spring now seek out company. The birds join in a foraging flock that includes adults as well as the young that hatched during the summer. Other species also may join in, such as Plain Titmouse on the West Coast or Tufted Titmouse in the East. Bushtits, Ruby-crowned Kinglets, and even Downy Woodpeckers may drift along as well, forming mixed-species flocks that forage together.

Come spring, the old intolerance reappears. The first sign usually comes in late winter, when males begin singing near their old territories on sunny days. Pairs begin dropping out of the flock. Instead of ten chickadees coming to your feeder, only two appear. The flock soon dissolves, and individual pairs stake out their old territories.