On several occasions this winter I’ve been out walking my dog when I’ve encountered a scene out of an Alfred Hitchcock thriller — huge flocks of birds all swarming around one or more bare-branched trees.

By Bill Lawyer    

On several occasions this winter I’ve been out walking my dog when I’ve encountered a scene out of an Alfred Hitchcock thriller — huge flocks of birds all swarming around one or more bare-branched trees.  
They find perches, and then start making a racket that sounds like large numbers of leaf blowers and rock hammers roaring in unison. It can be deafening.  

Are they out to get me? What are they doing?

Actually, being part of the YouTube generation, my real first thought was that these noisy, swarming behaviors reminded me of a flash mob in action.  

Wikipedia defines a flash mob as “a group of people who assemble suddenly in a public place, perform an unusual and seemingly pointless act for a brief time, then quickly disperse, often for the purposes of entertainment, satire, and artistic expression.”

On every occasion where I encountered an avian flash mob, they were gone by the time I got back from my walk. And if there was a point to their behavior, it wasn’t readily evident.  

Where did they go? What did they do to the trees?

Truth be told, I have seen such behaviors many times over the years.  Particularly as a kid in the fields around my grandfather’s farm near Gettysburg, Pa. In those cases, it was easy to see what the birds were up to — gleaning grain that the harvesters had left behind. Even bare trees, such as sweet gum, scholar, and plane trees, have seeds still attached to the branches.  

Chris Williams, a University of Delaware associate professor of wildlife ecology, says that flocking provides the birds a great deal of protection against birds of prey.  

And, a large flock also promotes greater feeding efficiency because the birds share information about food sources. “Blackbirds are known to be great communicators,” says Williams.

Roosting in large flocks provides protection against the cold and keeps other types of birds from encroaching on their territory. And when it comes time to migrate, traveling in a flock can be more energy-efficient from an aerodynamic standpoint. Some of the most common winter flocking birds are blackbirds, starlings, and shore birds.

What’s also interesting is that the old expression “birds of a feather flock together” is not really accurate. In many cases, various species — not of a feather — actually flock together.  

Kentucky naturalist Tom Pelletier says that there are two types of flockers — leaders and followers. The leaders tend to be larger species, such as titmice and chickadees, whereas the smaller birds, such as sparrows, wrens, and nuthatches, tend to be followers. By flocking with the larger birds, they get more protection and greater access to food sources. Scientists theorize that the leaders tolerate the followers because it would take too much work to “lose their followers, so they mostly ignore them.”  

But it’s not that easy to ignore the winter flocking birds, when their flocks become swarms of avian flash mobs, right in our backyards.