I have had lots of inquiries this fall about the lack of birds at bird feeders.  I don’t think Hurricane Irene or other natural phenomena have caused bird populations to plummet.  Rather, I think that our resident birds are finding enough food in nature during our mild and mostly snow-free fall so far.  I have hopes that we will get a nice influx of Common Redpolls and Pine Siskins this winter throughout our state.

An obvious difference in birds from breeding season to the winter is the increase in flocking behavior. During the breeding season, a pair of birds often occupies a nesting territory for the exclusive use of themselves and their young.  This territorial behavior breaks down after the nesting season and flocking behavior is commonly observed in the fall, persisting until the following spring.

What is the advantage of flocking?  Ornithological research has indicated two major advantages of this social behavior.  The first is an increase in foraging success, that is an increase in the success of finding food.  Food abundance for many birds is typically much reduced in the winter in comparison to the bounty of summer.  Furthermore, food in the winter tends to be patchy.  The food, such as acorns or birch seeds, may be abundant in one small area but non-existent in nearby areas.

In such cases where food is rare and patchy, flocking can be a real advantage to birds in locating the highly dispersed food.  With many eyes searching for food, it is likely that a food bonanza will be located that might well be missed if only one or two birds were searching the same area.

Even though the food will need to be shared among a number of birds, a modest meal is better than no meal.  Sometimes, it pays to cooperate.

The second advantage of flocking is an increase in the detection of predators.  With many pairs of eyes searching for Sharp-shinned Hawks or Northern Shrikes, flocking land birds stand a better chance of seeing those predators.  Watch the American Goldfinches, Black-capped Chickadees and other birds at your feeder.  You can see each bird spends a good bit of time looking around, ever vigilant against predators.

Both of these advantages of flocking may be realized for a flock.  Actually, there may be an interaction between these two benefits.  With lots of birds keeping a watch out for predators, each individual in a large flock devotes less time to searching for predators and more time in searching for food.  An individual bird would have to spend much more time being vigilant and therefore have less time to forage.

A flock, like many human families, is not free of conflict.  Often times within a flock, one can observe a pecking order or hierarchy in the flock.  One bird is dominant to all in the flock; the second bird in the pecking order dominates all but the top bird and so on down to the most subordinate bird that dominates no member of the flock.

Birds rarely have to resort to fighting to claim their position in a pecking order.  A dominant bird may simply make a threatening gesture and the subordinate bird will make a submissive gesture.  As an example, the Jackdaw (a Eurasian member of the crow family) shows submission by bending its head low and turning the nape of its neck toward the dominant bird.

Black-capped Chickadees provide a nice local example.  In a winter flock, the dominant bird is the single adult male in the flock and its mate is the second-highest ranked individual.  The remaining flock members are juvenile birds, none of which are the offspring of the adult pair.  These juveniles interact with each other during the fall to establish a strict pecking order.

[First published on December 11, 2011]