In most forested areas of the planet, whether temperate latitudes or in the tropics, insect-eating birds often form flocks of several species. These flocks are familiar to every birdwatcher in Europe and North America, for instance, and are composed of chickadees (which are called "tits" in Europe) with some small woodpeckers and other insect-eating species.
In temperate latitudes, these flocks are largely confined to the nonbreeding season, which is to say, from the fall through the winter.
In the tropical rainforests of the world, mixed-species flocks of insect-eating birds exist all year round, in breeding season and outside the breeding season. In all the world, the mixed-species flocks of the Amazon rainforest are the most complex known, and of the Amazonian flocks, those of SE Peru, particularly in the Manu and Tambopata areas, appear to be not only the most complex bird flocks in the world, but also the most complex multi-species assemblages of any group of organisms on Earth.
In Manu, research that I carried out between 1976 and 1983 showed that mixed species flocks include 103 species of forest birds, including virtually every species that actively searches foliage for insects. I also found that up to 70 species of birds can be found in one mega-flock at the same time. These mega-flocks are found normally only from about 1100 am until 230 pm in tall, lowland forest, and they are result of the joining together of a permanent understory flock, an entirely separate and permanent canopy flock, and a temporary flock of fruit-eating tanagers. |
