Rufous-capped antthrush

Appearance

The "Formicarius colma" is generally a small bird, averaging around 18 cm with males weighing between 38 and 49 grams and females between 41 and 49 grams. Males are marked by a black forehead, rufous-colored crown and nape, with the crown including a variable amount of black feathers. Its back, rump, and wings are olive-brown color with a dusky brown tail and black on the neck, throat, and sides of the head. The upper breast is a dark black that merges into a dark gray on the lower breast while the belly and flanks are a paler gray with a brown wash. Underwing coverts are marked by a mix of black and cinnamon with the inner webs of remiges being dusky with a broad cinnamon bar across the base. Facial features include a brown iris and black bill while the tarsus vary from light gray-brown to a purplish-gray. The female is largely the same as the male, being marked with a white throat rather than the black seen in males. The four subspecies differ slightly from each other; the "nigrifrons" largely resemble "colma" but with more black on the head, the "amazonicus" resemble the "nigrifrons" but smaller with a deeper rufous head, short tail, and browner upperparts, and the "ruficeps" having an extensively rufous head. Juvenile rufous-capped antthrushes are marked by a white throat and black spotting.

Distribution

The "F. colma" is found in east Colombia, south and east Venezuela, the Guianas, and in Brazil north of the Amazon while the subspecies "F. nigrifrons" are found east of Ecuador, east of Peru, north of Bolivia, and south of the Amazon. "F. amazonicus" is found in Brazil south of the Amazon, from east Madeira to north Maranhão, and south of Ji-Paranã and Mato Grosso. "F. ruficeps" is found on the coastal east and southeast of Brazil from Pernambuco to Rio Grande do Sul.

Status

According to the IUCN Red List of Threatened Species, rufous-capped antthrushes are considered of least concern and are not globally threatened. They are generally rated as uncommon to fairly common based on location and inhabit many protected zones. "F. colma" are fairly common in Ecuador, Peru, Colombia, Venezuela, and in the Guianas and rare in the Rio Grande do Sul.

Behavior

The song of the rufous-capped antthrush is generally a 4 to 6 second long, fast, even-paced trill of about 14 notes per second. This song is between 2.2 and 3kHz, with this frequency being speculated as optimal for communication in thick, humid underbrush. The call of the rufous-capped antthrush is described as a single, clear "psee-eh" or "pier," while the song is described as a  ""re-e-e-e-e-e-e-e-e-e-e-e-e-e-ee-ee-ee-ee-ee"".

Habitat

The rufous-capped antthrush are widespread, predominately preferring the cooler, shady floor of "terra firme" forests, although they can occasionally be spotted inhabiting traditional forests and savanna forests. While they generally occupy the lowlands to 500m and locally to 1100m, interspecies aggression between the rufous-capped antthrush and "F. analis" has been observed to induce altitudinal displacement, with "F. colma" fleeing to higher and drier ravines and ridges while the "F. analis" occupy the lower lands. Additionally, in Manu, the black-faced antthrush, being both larger and more population-dense, dominate over the rufous-capped antthrush. While the two species frequently overlap due to "F. colma's" large distribution, the song of the "F. colma" has been reported to induce an aggressive response from the black-faced antthrush while the song of the black-faced antthrush causes recession of the rufous-capped antthrush, indicating further interspecies aggression. Other than interspecies aggression, the driving factor controlling the rufous-capped antthrush's distribution is poorly understood, as they are believed to be a sedentary species.

Reproduction

Very few rufous-capped antthrush nests have been found. Those found are composed of a crude arrangement of roots and leaves placed into a cavity. The clutch size of "Formicarius" typically consists two white, ovoid eggs that become stained and blotched soon after laying. Two eggs from one clutch were measured to be 28.6-32.3 x 21.8-24 mm. Rufous-capped antthrush hatchlings emerge altricial with long, spreading gray down. Juveniles are typically hatched around October, however, in Colombia they emerge in May. In Brazil, males with enlarged testes are also seen in October while they are observed in April near Venezuela. Juveniles in Peru were flushed out of the nest in November.

Food

The diet of a rufous-capped antthrush consists of ants and grasshoppers. They hunt by walking slowly and tactfully on the forest floor, picking prey off of leaf litter before flicking it away with their beaks. They usually hunt alone but have been observed hunting near each other in small groups. They are frequently seen alone or in small groups on the periphery of ant swarms. Additionally, "Formicarius" have also been known to occasionally eat snakes.

Predators

Currently, the largest threat to the rufous-capped antthrush is loss of habitat through mining and deforestation. While "F. colma" is currently not globally threatened, these activities have been shown to drive "F. colma" and other "Formicariidae" from their habitats. Because "F. colma" are sedentary, this makes it difficult for them to escape.