The story of how the Pilgrims shared a feast with Native Americans at our nation’s first Thanksgiving celebration is full of inaccuracies, but there are plenty of stories of shared feasts that we can tell without ignoring important facts or inventing new ones. Perhaps no group feeding situation is as well studied as mixed-species foraging flocks of birds.
Mixed-species foraging flocks of birds have been described in terrestrial habitats all over the world, and they are just what the phrase suggests—a variety of bird species eating together. These groups are common because individuals have so much to gain by belonging to them, including an increase in the amount of food they consume.
Foraging in one of these flocks improves the chances of finding high-quality food sources. A group of birds may be able to gain access to a good feeding site because they can overwhelm territorial defenses that would cause a single individual to be kicked out of an area. Because the individuals in a group are moving through the landscape together, it’s easier for them to avoid areas that have recently been exploited, leaving little food available. Additionally, there may be less competition than in a flock made up of members of the same species because they are not all eating the same type of food. One species may even flush prey that another species feeds on. Birds can sometimes learn about new food sources by observing members of other species as they eat.
If increased foraging efficiency is a driving force behind the formation of mixed-species foraging flocks, then this flocking behavior should be related to food abundance. One simple experiment found this to be true by showing that when food was extremely plentiful, mixed-species foraging flocks were less likely to form. In the study, one area of forest was left undisturbed, but an adjacent one was provisioned with large amounts of beef suet and sunflower seeds. A number of birds commonly found in mixed-species foraging flocks, including woodpeckers, nuthatches, chickadees, creepers and titmice, were less likely to join groups in the provisioned area than in the natural area.
In addition to the direct feeding benefits, being in a mixed-species foraging flock offers birds enhanced safety from predation. With more eyes and ears alert to predators, there is a greater chance that dangerous natural enemies will be spotted in time for the birds to take evasive action. This combined vigilance is even more advantageous when different species, with different sensory abilities, share sentry duties. Also, being in a large group may make it harder for a predator to zero in on a single target, and lowers the probability that any particular individual will be taken by the predator. The improved ability to detect predators and the shared responsibility for doing so may mean that individual birds are able to spend less time watching out for danger and more time actually foraging.
At Thanksgiving time and always, take it from the birds—feasting together makes the eating better.