Capable of weighing as much an adult human, the capybara is the world’s largest rodent. It is often seen wallowing on the banks of the Tambopata River by ecotourism visitors traveling by boat through the National Reserve area, and in surrounding forests. In additional to riverbanks, it also inhabits areas close to streams and marshes. As highly social animals, capybaras live in groups of between ten and thirty individuals.
As groups of capybaras roam the riverbanks of the Amazon basin, they are accompanied by flocks of black birds. These are smooth-billed anis (Crotophaga ani), and the two species share a mutual relationship. The smooth-billed ani benefits by eating the capybaras’ external parasites, and the capybaras benefit from the cleaning service provided by the birds. In this way, the two species live in complete harmony, and if for any reason this symbiotic relationship were to be broken, the wellbeing of both species would be affected.
While they look a little like large songbirds, anis are actually related to roadrunners and cuckoos. The smooth-billed ani is an unusual looking bird. A glossy, coal-black in color, with a long tail, it can be identified easily from its curiously flattened bill, which exhibits a heightened ridge on the upper part, while the lower edge of the bill is more sharply angled. They will often use their oversized upper mandible to knock away foliage during foraging.
It is the smooth sides of the bill which give this species its common name and distinguishes it from the smaller groove-billed ani. The smooth-billed ani is a mid-sized bird, measuring up to 36 centimeters (14 inches) in length, and weighing up to 133 grams (just under 5 ounces). Because it is a gregarious bird and tends to live in highly vocal groups, the smooth-billed ani can also be identified by its distinctive call, which has been described as a hawk-like whistle.
Smooth-billed anis are widespread, mostly occupying open habitats within subtropical and tropical forest ecosystems, all the way from Florida in the United States, through Central America and the Caribbean, to the Amazon forests of South America. Interestingly, in the breeding season several pairs of anis will build a bowl-shaped communal nest measuring up to 6 meters (almost 20 feet) in diameter. Several females will lay their bluish-white eggs in this nest, and then share in the task of incubating the eggs and feeding the young.
Cumbersome in flight, the smooth-billed ani is quick on its feet, and therefore prefers to feed on the ground. Although it will also feed on termites, insects and -on occasion- small lizards or frogs, the most distinctive feature of the smooth-billed ani’s feeding behavior is its symbiotic relationship with capybara. While other bird species may fly close to capybaras in order to catch the insects that tend to gather around the rodents, the smooth-billed ani specializes by feeding on the ticks and other external parasites which would otherwise infest this semi-aquatic rodent.