Where are the birds? I’m sure I have been asked this question at least 20 times in the last month. Lots of people are finding that many of our familiar, common birds have abandoned our feeding stations.
Fall migration is drawing to an end, so many of our summer birds have moved on to warmer quarters for the winter. However, most birds that frequent our feeders are residents. Many observers have noted the dearth of black-capped chickadees, tufted titmice, white-breasted nuthatches, American goldfinches, downy woodpeckers and hairy woodpeckers. Where did they go?
The abandonment of bird feeders does not indicate a precipitous decline in bird populations. The phenomenon of resident birds forsaking handouts actually occurs every fall. This year’s pattern is, however, one of the most striking ones in my memory.
To understand it, we need to realize that birds do not rely on our sunflower seeds and millet for their existence. Our feeders provide only a fraction of a bird’s daily energetic demands.
Birds wander throughout a foraging area to feed from many sources. The reason is basically uncertainty. Any given food source can be depleted in short order. To spread the risk, birds do not depend on a single source.
Shrubs, trees and many herbs set seeds in the late summer and fall. This banquet of acorns, birch seeds, winterberries and other bird delicacies is too much to resist for most of our common birds. Sunflower seeds seem to be pretty low on the preference list compared to natural food, so our feeders go unvisited in the early fall.
I’m willing to bet you are seeing fewer squirrels and chipmunks at your feeding station now as well. These rodents are taking advantage of the autumn pulse of natural seeds, too.
Natural food is notoriously patchy. When resources are clumped, ecologists know that individuals can find more food by foraging as a group. One bird in a flock is likely to happen across a rich, localized source of food that is then shared with other members of the group. A lone forager would hit the jackpot if it discovered a rich food source, but like the lottery, the chance of a lone bird finding a mother lode of food is slim.
The common feeder birds listed earlier form mixed-species feeding flocks in the fall that persist well into spring. A flock offers the dual advantage of finding patchy food and avoiding predators because of the many eyes on the alert for sharp-shinned hawks and other predators.
Black-capped chickadees are the nuclear species in a winter flock. A nesting pair of chickadees maintains a summer territory of one to four acres. In the fall, it expands to include up to 25 acres. Mom and dad kick the young ones out but are joined by eight to 12 juvenile chickadees from neighboring parents. For the juveniles, this winter flock provides a matchmaking opportunity. Most will have formed a pair bond with another flock member by spring and will go off to nest for the first time in May.
The chickadees in a winter flock are usually joined by a couple tufted titmice, a couple downy woodpeckers, a few white-breasted nuthatches or red-breasted nuthatches, and even a brown creeper or golden-crowned kinglet. If your feeding station falls within a winter territory, it is possible that the flock has not even discovered it yet.
A possible contributing factor is a phenomenon called partial migration. Depending on food resources, some but not all members of a resident species may move southward.
Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at
whwilson@colby.edu
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