Cercomacroides

Cercomacroides are small to medium-sized antbirds. Their body length is about 12 to 14 cm, and they weigh between 15 and 25 grams.^[10] Their bills are black or dark grey. The upper bill is slightly curved, and the lower bill is straight. They have short wings and cannot fly far. They usually move by hopping or short flights. Their tails are long and slightly wedge-shaped. Their wings are short and round, which helps them move quickly through thick plants. Their legs are strong and dark grey or lead-colored. This helps them climb and jump on the ground or between branches.^[1]

Male birds are mostly black or dark grey. Their plumage is even, with no clear markings. Their tail feathers are one dark color without white tips. This is a key difference from the Cercomacra genus. Female birds have warmer colors, such as orange-brown, yellow-brown, or olive. The color difference between males and females is clear. Sexual dimorphism is common in this genus.^[11] The feathers on the face are dense and provide protection. Young birds have lighter plumage, usually brownish-yellow or olive, with pale edges on the feathers. It is hard to tell male and female chicks apart in the early stages.^[10]

This table compares six species within the genus Cercomacroides, outlining key differences in male and female plumage and distinctive features used for identification.^[12][13]

Species of the genus Cercomacroides are found from southern Central America to northern South America. They are mainly distributed in the Amazon Basin and on the eastern slopes of the Andes Mountains. Their range includes southern Mexico, Costa Rica, Panama, Colombia, Venezuela, Ecuador, Peru, and northern Brazil.^[11][2] While some species share overlapping areas, most have specific regional centers.

The genus Cercomacroides now includes the following 6 confirmed species:^{[13][2][14][15][16][17][18]}

Image	English Name	Scientific Name	Distribution Area
	Willis’s Antbird	Cercomacroides laeta	Central Amazon in Brazil, northeast of Pará State
	Parker’s Antbird	Cercomacroides parkeri	Central-west Colombia, Andes Mountains (around 1100–1950 m elevation)
	Blackish Antbird	Cercomacroides nigrescens	Tropical forests in northern South America
	Riparian Antbird	Cercomacroides fuscicauda	Eastern to southeastern Colombia, northwestern Brazil and Peru
	Dusky Antbird	Cercomacroides tyrannina	From southeast Mexico, through Central America, to northwest Ecuador and many parts of the Amazon
	Black Antbird	Cercomacroides serva	From southeastern Colombia to northern Bolivia and northern Brazil

According to the IUCN Red List, all six species of Cercomacroides are currently classified as “Least Concern” in terms of global conservation status.^[5] They are mostly found in tropical rainforests and secondary forests in South America. Some species can live well in disturbed habitats such as forest edges, secondary growth, and bamboo areas. This makes them less sensitive to human activities compared to other forest birds.^[12]

However, there are still clear differences in range and population status among the species. The Black Antbird, Dusky Antbird, and Riparian Antbird have wide distributions and stable populations. They are found in several national parks and are considered common or fairly common.^[13][17][18]

In contrast, Parker’s Antbird and the Blackish Antbird have smaller ranges. They mostly live in specific elevation zones in the Andes Mountains. Their population sizes are limited, and they face some risk from habitat loss.^[15][16]

Overall, this genus shows good adaptability to secondary forests, which gives it more resilience than many other understorey birds.^[1]

Cercomacroides was originally part of the genus Cercomacra. For many years, Cercomacra was seen as a uniform and monophyletic genus based on its physical traits. However, as scientists studied the behavior and vocal patterns of antbirds more closely, they began to question whether Cercomacra was truly as unified as it appeared.^[19]

In the early 1990s, scientists divided the genus Cercomacra into two informal groups. They used female plumage and song behavior to make this division. The two groups were called the “nigricans group” and the “tyrannina group.” However, this division had no strong phylogenetic evidence. So, it was not widely accepted.^[19]

In 2014, Tello and colleagues published a study in the Zoological Journal of the Linnean Society. They used mitochondrial and nuclear genes (ND2, ND3, CYTB, and FIB5) to analyze relationships. They built a phylogenetic tree using maximum likelihood and Bayesian methods. Their results showed that Cercomacra was polyphyletic. It included two unrelated lineages.^[20]

One of these lineages, led by Cercomacra tyrannina, was moved to a new genus: Cercomacroides.^[3] The South American Classification Committee (SACC) approved this change under Proposal No. 638.^[21]

The name Cercomacroides comes from three Greek roots: cerco- meaning “tail,” -macr- meaning “long,” and -oides meaning “similar to.”^[22] The full name means “a group similar in appearance to Cercomacra,” highlighting its visual similarity while recognizing its separate evolutionary lineage.

The new genus originally included five species: C. tyrannina, C. serva, C. nigrescens, C. laeta, and C. parkeri. In 2014, Mayer and colleagues identified fuscicauda as a separate species from C. nigrescens (SACC Proposal No. 636),^[23] increasing the total number of species in the genus to six.^[24]

Antbirds in the genus Cercomacroides mainly feed on insects. Including beetles, grasshoppers, lepidopteran larvae, orthopterans, homopterans, and spiders, as well as other arthropods.^[25] By eating insects, Cercomacroides species act as natural pest controllers in the rainforest. They help reduce insect damage and support the balance of plant communities. These birds mostly live in the understorey of tropical lowland rainforests. They prefer dark, humid areas with dense vegetation, such as primary forests, mature secondary forests, and edges of degraded woodlands.^[1][12]

They are usually seen alone, in pairs, or in small family groups.^[1] They forage mainly between ground level and 5 meters high.^[12] They do not usually join mixed-species flocks. Their behavior is active but calm. They move in short hops, often pausing for a few seconds between jumps to look for prey. Their body posture can vary from almost horizontal to nearly upright, and their tails are held flat or slightly raised. While foraging, they may gently flick their wings. They search for prey among shrubs, fallen logs, vines, and leaf litter. Sometimes, they jump to the ground and flip over leaves to find food. Their movements are quick and flexible, which helps them move through the complex forest understory. They often pause briefly to watch for prey, then quickly strike from behind leaves, under branches, or among fallen leaves on the ground. Sometimes, they hang upside down from branches or climb vines to catch food.^{[13][14][15][16][17][18]}

Some species, such as C. tyrannina and C. nigrescens, sometimes follow army ants like Eciton burchellii.^[16][17] These ants move quickly through the forest and flush out many small animals, creating a chance for birds to catch exposed prey. Cercomacroides birds often forage in front of the ant swarm, catching insects that try to escape.^[1] This behaviour is called "ant-following foraging." However, Cercomacroides are not fully dependent on this method. They are considered "facultative ant-followers," meaning they only show this behavior in certain areas and at certain times.^[26]

These birds are highly adaptable and can forage successfully in both primary and secondary forests. They play an important role in the food web of the tropical forest understory.^[1][18][17]