Mixed-species foraging flock

A mixed-species feeding flock, also called a mixed-species foraging flock, is a group of birds from different species that stay together while searching for food. These birds are usually insectivorous, meaning they eat insects, and they form a special kind of flock that is different from groups of birds that simply gather where there is lots of food.

Scientists are still trying to understand exactly how these mixed groups first come together. Some believe that certain "nuclear" birds lead the way and attract others to join. The shape and layout of forests may also help these flocks form. For instance, in Sri Lanka, the calls of the greater racket-tailed drongo might help bring birds together, while in parts of the American tropics, groups of golden-crowned warblers might serve a similar purpose.

These flocks are fascinating because they show how different kinds of birds can work together and help each other while looking for food.

Composition

Mixed-species foraging flocks usually form around a special group of birds called the "nuclear" species. These birds help start and keep the flock together. They often search for food in many different ways and like to stay in groups. Other birds, called "associate" or "attendant" species, follow the flock when it enters their area and seem to benefit from it.

There are also birds known as "sentinel" species in these flocks. Unlike the nuclear birds, sentinels are usually not social and catch insects by flying. Their job is to watch for danger and warn the other birds if a predator is near.

Benefits

Birds in mixed-species flocks can work together even though they usually compete for the same food. When birds of different species fly together, they can find food more easily. They spot food better, avoid places where food has already been taken, and scare insects out of hiding.

Another reason birds join these flocks is to stay safe from predators. Being in a group makes it harder for predators to pick out a single bird to attack. The more birds there are, the safer each bird feels.

Costs

Mixed-species feeding flocks can have some downsides for the birds involved. Some birds might leave their best feeding spots just to follow the flock, even if it means going to a place where there is less food. They might also have to change the way they search for food to fit in with the group. Another possible problem is a higher chance of encountering kleptoparasitism, where one bird might steal food from another.

In the Holarctic

In the North Temperate Zone, mixed-species foraging flocks are often led by Paridae (tits and chickadees). They are frequently joined by nuthatches, treecreepers, woodpeckers like the downy woodpecker, and kinglets. In North America, Parulidae (New World "warblers") also join these groups. All these birds are insect-eating, and this behavior is especially common when they are not breeding.

The benefits of staying together are not fully known, but it seems to help birds stay safer from predators. Smaller, less watchful birds like vireos and woodpeckers may feel safer in a group. The flock can also catch food more efficiently, as prey that escapes one bird might be caught by another.

In the Neotropics

Insectivorous feeding flocks are most developed in tropical forests, especially in the Neotropics. Here, certain birds like black-throated shrike-tanagers in southern Mexico or three-striped warblers in Central America often lead these flocks. In South America, leaders can include antbirds, antshrikes, and various Parulidae such as golden-crowned warblers.

These flocks usually consist of many small, diurnal insect-eating birds from different families, such as cardinals, Passerellidae, and Thraupidae. Some birds, like buff-throated warbling finches, may join these flocks without starting them. The flocks move through the forest at a slow pace, with each bird species foraging in its preferred area.

In the Old World tropics

In tropical Asia, especially in places like Sri Lanka, mixed-species flocks can include hundreds of birds that stay together all day. When these flocks appear, the quiet jungle fills with the calls of birds such as the orange-billed babbler and greater racket-tailed drongo, along with others like the ashy-headed laughingthrush.

In the Philippines, particularly in the Cordillera Central of Luzon, flocks often include bar-bellied cuckooshrikes, Philippine fairy-bluebirds, and violaceous crows. Sometimes, Luzon hornbills join too. African rainforests also have these flocks, with core birds like bulbuls and sunbirds, and other birds such as the red-billed dwarf hornbill and tit-hylia joining in.