ANT THRUSHES: Formicariidae

PHYSICAL CHARACTERISTICS

Ant thrushes, also called antbirds, antcatchers, antpittas, antshrikes, or antwrens, are a family of small to medium-sized perching songbirds found in the rainforests of Central and South America. There are two major divisions within the ant thrush family, based on where the birds spend most of their time. About fifty-six species live on or near the forest floor and as a group are called ground antbirds. About 188 species live in the canopy, or forest treetops. These birds are sometimes called typical antbirds.

The bodies of antbirds vary in length from 4 to about 15 inches (10 to 38 centimeters). Some antbirds have short, stiff tails that they hold upright, while others have tails as long as their body that droop. Ground antbirds tend to be larger than canopy-dwelling antbirds and have longer, stronger legs and short toes for running and hopping. Antbirds that live in the canopy have developed special longer toes that allow them to grip thin branches for long periods without using much energy.

Antbirds do not migrate, or move seasonally from one region to another. As a result, they have evolved, changed over time, to have stubby, rounded, relatively weak wings that are best suited for flying only short distances.

Antbirds eat mainly insects. Their bills are specially designed for this task. Antbird bills curve slightly downward and in some of the larger species have a hook at the tip. Larger species of antbirds also have a "tooth," or rough spot, inside the bill that helps them to hold on to or tear up food. Smaller antbirds have a smooth bill and no "tooth."

Antbirds are not the most colorful birds in the rainforest. In fact, they are rather dull. They range in color from black to gray to brown. Male and female ground antbirds usually look quite similar. However, canopy-dwelling males are often black or gray with some white feathers, while females are brown and often marked with a pattern of light and dark spots. Their coloring makes them difficult to see on the forest floor or among the shifting shadows and sunlight of the canopy.

GEOGRAPHIC RANGE

Antbirds are found in tropical and subtropical rainforests from southern Mexico to northern Argentina. However, the greatest number of species is found in the rainforest of the Amazon River basin in Brazil and the Orinoco River basin in Venezuela.

HABITAT

Antbirds live in damp, shrubby, forested regions and woodland areas in the tropics, including areas where the original trees have been cut down and new trees are appearing. Species in this family can be found from sea level to high on forested mountains, up to 10,900 feet (3,300 meters).

DIET

Antbirds are insectivores, or insect eaters. They eat many different insects and insect-like bugs including crickets, beetles, spiders, centipedes, and lice. Larger antbirds also eat snails, frogs, lizards, small snakes, mice, and young birds. They use their strong bill and "tooth" to kill this larger food. Some species eat fruit and seeds in addition to insects.

SOS FOR DANGER

Most species of ant thrushes have white spots on their back that are hidden under their wings when they are resting or calm. When these birds think that they are in danger, they flash these white spots in a quick off-and-on pattern. Scientists believe this is a kind of Morse code that lets other birds in the area know that something threatening is nearby.

BEHAVIOR AND REPRODUCTION

Antbirds were given their name because of their special feeding behavior. In the rainforest colonies of ants often move together in huge swarms or columns when they are hunting for food. As the ants move, they stir up insects and small animals, such as mice and lizards. Antbirds have learned to take advantage of the movement of these ants, especially swarms of red army ants and black rain ants. The antbirds follow a column of moving ants and pick off insects and small animals that are trying to get away from the hungry ants. In a sense, the ants do the birds' hunting for them.

Ant colonies are so important to antbirds that that older male birds will drive younger, weaker birds out of their territory in order to keep them away from the ant colonies. During nesting season, antbirds usually wait for ant columns to pass their nests, but other times of they year they actively look for and follow moving ant colonies.

Antbirds also perform a grooming or cleaning behavior that involves ants. The birds pick up ants in their bills and rub them into their feathers. This is called "anting." Scientists believe that when the ants are crushed, their bodies release formic acid, which kills parasites, organisms that live on other organisms, living on the birds' feathers. A few antbird species also allow live ants to crawl through their feathers and eat insects that are attached to their skin.

Although much is not known about the reproductive behavior of antbirds, it appears that they mate with a single partner for life. The location and shape of antbird nests varies depending on the species. Ground antbirds often build closed, rounded nests directly on the forest floor. Other species build deep cup-shaped nests on low branches. Some species use holes in trees or rotting logs.

Antbirds usually lay two light-colored eggs that hatch within fourteen to seventeen days. Both parents share the job of incubating, sitting on the nest to provide warmth for chick development, the eggs. Young antbirds are able to leave the nest and hunt for food soon after they are born.

ANT THRUSHES AND PEOPLE

The ant thrush family is of interest mainly to ornithologists, scientists who study birds, and birdwatchers interested in ecotourism, travel for the purpose of studying wildlife and the environment.

Flying Through the Mail

In 1980 the Central American country of Belize featured the barred antshrike on its 25 cent postage stamp.

CONSERVATION STATUS

In 2003, four species of antbirds were considered Critically Endangered, facing an extremely high risk of extinction, or dying out, in the wild. These were the fringe-backed fire-eye, the Rio de Janeiro antwren, the Alagoas antwren, and the Rondonia bushbird. Sixteen other species were considered Endangered, facing a very high risk of extinction, and eleven species were classified as Vulnerable, facing a high risk of extinction. The main reason these birds are at risk for extinction is loss of habitat due to human activities such as farming, mining, and development.

BARRED ANTSHRIKE (Thamnophilus doliatus): SPECIES ACCOUNTS

Physical characteristics: Barred antshrikes, sometimes called Chapman's antshrikes, are small, noisy birds about 6 inches (15 centimeters) long. Males are black with white bars and a black crest of feathers on their head. Females have black stripes, but are cinnamon or reddish brown colored, instead of white, and have a brown crest. Both males and females have yellow eyes, long tails, and strong black bills.

Geographic range: The barred antshrike is one of the most common antbirds. It can be found living year-round from southern Mexico to northern Argentina east of the Andes Mountains. Although it is widespread in Brazil, it is not found in the center of the Amazon rainforest.

Habitat: Barred antshrikes live on the edges of the tropical rainforest, but not deep in the center of the forest. These birds can be found in scrubland, along roads, in open woodland and clearings, and in gardens or abandoned lots. They live in both humid and dry areas at elevations between 330 and 6,600 feet (100 and 2,000 meters).

Diet: Like all antbirds, barred antshrikes eat insects and insect-like bugs. They normally hunt for food with mixed groups of other birds in an area between the lowest bushes and the treetops.

Behavior and reproduction: Barred antshrikes mate for life with a single partner and tend to stay together throughout the year. They usually lay two eggs in a nest made of grasses. Nests are often built in low bushes. Both parents incubate the eggs and care for the young.

Barred antshrikes and people: Barred antshrikes have no special significance and little economic impact on people. They are of interest mainly to birdwatchers and ecotourists.

Conservation status: Barred antshrikes are not threatened. They are common birds found across a wide area of Central and South America. ∎

GRAY ANTBIRD (Cercomacra cinerascens): SPECIES ACCOUNTS

Physical characteristics: The gray antbird is a small bird of about 6 inches (16 centimeters) with a rather long tail. It is dark gray with a white band at the tip of the tail.

Geographic range: Gray antbirds are found in the rainforests of northern South America, including Guyana, the southern part of Venezuela, parts of Colombia and Ecuador, eastern Peru and northern Bolivia. They are most abundant in the Amazon River basin of Brazil.

Habitat: Gray antbirds live in the forest canopy in dense rainforests and on heavily forested mountain slopes below an elevation of 2,300 feet (700 meters).

Diet: Gray antbirds eat insects and insect-like bugs.

Behavior and reproduction: Gray antbirds form pairs that stay together, although they sometimes hunt for food in a group with birds of other species. Little is known about their nesting habits.

Gray antbirds and people: Gray antbirds are of interest mainly to birdwatchers and ecotourists.

Conservation status: Gray antbirds are not threatened; they are abundant in many places. They are found across a wide area of northern South America. ∎

FOR MORE INFORMATION

Books:

Hilty, Steven L. Birds of Venezuela. Princeton, NJ: Princeton University Press, 2003.

Ridgley, Robert S., and Guy Tudor. The Birds of South America. Vol 2, The Suboscine Passerines. Austin, TX: University of Texas Press, 1994.

Web sites:

Gleyzer, Artem, Seth Weith-Glushko, and Abhiram Vijay. "Project:Antbird." Academy for the Advancement of Science and Technology and The National Zoo. http://www.bergen.org/Smithsonian/Antbirds/homeantb.htm (accessed on April 24, 2004).

Robertson, Don. "Bird Families of the World." CREARGUS@Monterey Bay. http://www.montereybay.com/creagrus/index.html (accessed on April 27, 2004).