New genus of antwren

Joseph Wolf first painted Plain-throated Antwren from specimens in 1857. Image: commons.wikimiedia.org.
Joseph Wolf first painted Plain-throated Antwren from specimens in 1857. Image: commons.wikimiedia.org.

With the world's largest avifauna, as well as the most mis-classified of avian taxonomies, the ongoing phylogenetic analyses of South American birds is constantly throwing up new genera and new species, whether by the splitting of already known species or plain discovery by exploration.

A wide-ranging, though not fully comprehensive examination of the antwren genus Myrmotherula has revealed three fairly unrelated clades, meaning that some of the species will have to be reassigned to at least one new genus.

The antbirds, antwrens, antvireos and antshrikes of the family Thamnophilidae are small to medium-sized passerines with relatively heavy bills, specialised in  following the huge swarms of ants that migrate through their native rain forests, often with well-adapted gripping feet for clambering through the under-storey following their prey. The antwrens themselves superficially resemble the true wrens Troglodytidae, but tend to move around in small groups and mixed flocks with other species, following the swarming ants.

Myrmotherula is traditionally held to contain up to 35 species, and others are likely to be added in time. They are small, short-tailed species but their morphological, behavioural and ecological differences have long suggested that they are not necessarily each others' closest relatives, and the new analysis has found that two species, Rufous-bellied Antwren M guttata, found north of the Amazon basin as far as Surinam, and Plain-throated Antwren M hauxwelli, from the Brazilian Amazon rain forest south of the river, are distinctive and closely-related enough to be given their own genus, Isleria.  

The new phylogeny, which used 39 Thamnophilid species in all, was based on both mitochondrial and nuclear genes and would appear to be fairly robust, though some species were not sampled. The two Isleria taxa are sister species most closely related to the Thamnomanes antshrikes. The new Isleria species are much smaller, usually forage away from the typical mixed-species flocks of the Amazon and have several key plumage and song differences, all of which make any merging with Thamnomanes untenable and are consistent with the differences between other Thamnophilid genera.

Bravo, G A, Chesser, R T and Brumfeld, R T. 2012. Isleria, a new genus of antwren (Aves: Passeriformes: Thamnophilidae). Zootaxa 3195: 61-67.