🧐Why do birds form mixed-species flocks❓❓
HAVE YOU EVER ENCOUNTERED A NOISY FLOCK OF DIFFERENT BIRDS FORAGING TOGETHER IN THE WINTERTIME?
If so, you have found yourself a mixed-species flock.
This flocking behavior among different species occurs all over the world and is most prevalent in the non-breeding season. If you live in the southeastern US, you have probably seen flocks that consist of Tufted Titmice, Carolina Chickadees, Blue-gray Gnatcatchers, Yellow-rumped Warblers, White-eye Vireos, and Downy Woodpeckers. If you observe the flock carefully, you may also find some Black-and-white Warblers foraging along tree trunks in search of hidden insects and other arthropods. Additionally, you may find a hovering Ruby-crowned Kinglet whose flamboyant crown feathers are only visible when the bird is agitated.
WHY DO DIFFERENT SPECIES OF BIRDS FORAGE TOGETHER?
To answer this seemingly simple question, researchers have conducted observational, experimental, and theoretical studies for a long time. It seems that most mechanisms that can explain this behavior come down to two benefits associated with mixed species flocking: foraging enhancement and antipredation. On the one hand, flock participants can learn from each other about the locations of food resources. On the other hand, foraging in a large group can lower your own risk of being attacked by predators, not only because you are less likely to be singled out but also because more eyes are watching out for predators (“many-eyes effect”). The foraging and antipredation benefits are not mutually exclusive to each other, as less time spent scanning for predators usually translates to more time spent foraging.
Now, one question might come to your mind: it seems that birds can achieve both foraging and antipredation benefits by flocking with their own species. Then why bother flocking with different species? Here are a few answers. First, different species differ in their foraging niche (foraging microhabitats, foraging maneuvers, and prey items). By foraging with a different species, you avoid competing with your own species that have the same foraging niche. Second, birds can gain foraging and antipredation benefits in ways unique to mixed-species flocks. For example, sallying species, which normally catch prey on the wing, can take advantage of the foraging maneuver of gleaning species, which normally pick prey from leaves or branches. When gleaning species travel through dense foliage, their movement scares up lots of prey items, which then become food for the sallying species that are in the same flock. Also, certain mixed-species flock participants are alarm-callers that are especially good at spotting predators and alarming other flock members. By closely associating with these alarm callers, other birds can reduce the risk of being predated.
Do mixed-species flocks sound interesting to you? As most birds wrap up their breeding season this year, be sure to take a walk in the woods and observe some flocks. How many species do you see in one flock? How many individuals do you count in each species? Which species do you think is the leader of the flock? I hope you have a fun time observing mixed-species flocks.