Did you ever hear the expression “Birds of a feather flock together”? They do, especially in fall and winter. One of my favorite parts about birding in the fall and winter is seeing these huge flocks. In my area I usually see hundreds of European starlings on telephone wires, brown-headed cowbirds on the ground, and American robins in the forest. Why do birds form such huge flocks when the weather gets cold? To find out, let’s think back to spring and summer.
Spring and summer is a very busy and competitive time for birds. The weather is warmer, food is more abundant, and breeding season begins. At a park I frequent, American robins can be seen running all over in the spring. They are all spread out and seem to be preoccupied with their own agendas. There are mates to attract, nests to build, and eggs to watch over. A bird will expend a lot of energy protecting and feeding their chicks. In the warmer months it makes more sense for birds to be in smaller family groups, like house sparrows and Florida scrub jays tend to do. Even cedar waxwings, almost always seen in larger groups, will separate during breeding season. Towards the end of summer molting begins. This is a dangerous time for most songbirds. Molting is when worn feathers are replaced by new feathers. Birds tend to want to lay low during molting to avoid predators. Therefore, large groups are not very advantageous.
Once cold weather hits, being in a huge flock has three benefits: food, safety, and warmth. Food sources become scarcer, so if birds are in a large group they can help each other find food. People use the expression “you eat like a bird” to mean that someone doesn’t eat much, but that idea is far from the truth! Birds become gluttonous in the winter and will try to eat as much as possible. If you ever watched a feeder cam or have a feeder in the winter you’re bound to see a lot of visitors. At my feeder house sparrows, Carolina chickadees, and white-breasted nuthatches will come continuously for hours, eating the food like it’s going out of style. The downside to this gluttonous behavior is that the more weight a bird carries the slower it is, and the more likely the bird itself will become a meal to a predator! If you’re a bird that is surrounded by a few hundred others, you have less of a chance of being eaten, and more of a chance of finding food to eat.
Another reason large flocks are beneficial in the winter is for warmth. When birds are in large flocks they can cuddle up and use body heat from others to help stay warm. Most songbirds also have down feathers, which are a fine layer under the exterior feathers that help insulate a bird against heat loss. But let’s say you’re a woodpecker, a kind of bird that doesn’t have down feathers. What other strategies can a bird use to keep warm? Birds can also stay warm by keeping one leg close to their bodies to conserve heat, or roost (rest) in a hole or crevice to get out of the wind.
Once spring arrives again the huge flocks of hundreds will disperse and the cycle will continue. I hope everyone enjoys seeing the large winter flock in their area. What large flocks are you seeing?