Some of the birds that inhabit our yards during the winter travel about in flocks. Among the birds that adopt this behavior are American robins, chipping sparrows, brown-headed cowbirds, common grackles, and red-winged blackbirds.
Being a member of a flock offers a bird many advantages. A bird traveling in a flock is less likely to be captured by a hawk, owl, or other predator. This is called the predator dilution effect.
Here is how it works. Should a Cooper’s hawk dive into a flock, it must select one bird and not be distracted by all of the others in the flock. This is often difficult to do when lots of birds are frantically trying to escape with the lives. As such, to be successful the hawk must target a single bird. If the hawk attacked the whole flock and simply lashes out trying to catch a bird, chances are all of the birds will fly away unscathed.
Another advantage to being the member of a flock is that it is extremely difficult for a predator to approach a flock of birds when hundreds, if not thousands, of pairs of eyes are poised to detect any potential danger.
In addition, flocks have a tendency to find food more readily than individual birds. In many cases, the older, more experienced members of the flock know the best places to find food and roost. This is a real bonus since food is often difficult to find in winter.
In addition, birds that expend as little energy as possible trying to locate food have a greater chance of survival during frigid weather. A bird in poor physical condition can easily succumb to the cold on frigid nights simply trying to maintain its body temperature.
I am sure you are familiar with the old adage, “There is safety in numbers.” As you can see, in the case of birds that flock together in winter, this statement is indeed true.