White-flanked Antwren

How to find it

Look for it in understory mixed flocks of small birds, on forest trails in the Caribbean lowlands and foothills. One Costa Rica guide finds it at most mature lowland forest sites on the Caribbean side, and at quite a few foothill rainforest sites. Flocks that hold antvireos and other antwrens are the ones to stay with, and the same flocks have held Streak-crowned Antvireo and Checker-throated Antwren. Patient watching is what found it for a birder at Laguna del Lagarto. Do not expect it on every walk: a tour group that found a pair on the Braulio Carrillo foothill loop trail was told it is not often met there, though it is well within the bird's range.

How to recognise it

This is a tiny antwren, about 9 to 10.5 cm long, with a short tail. Males show these marks:

Dark gray above and black below.

Black wings with white streaks and spots.

White flanks and white underside of the wing.

A hidden white patch between the shoulders, in males of the nominate form.

Females and young birds look different at first glance. They are brown above and yellowish cream below. Like the males, they still show white flanks and white under the wing, so those patches are worth searching for on any small bird in the flock. It is the only antwren with white flank patches.

What it sounds like

Recording: Rajan Rao, CC BY 4.0, source, read 4 Nov 2026.

Behaviour and diet

It eats small insects and other arthropods, which it picks from branches in the lower levels of trees. It usually occurs in small groups and joins flocks with other forest species. It also joins ant-following birds, and a Venezuelan source says it often tracks army ants.

It is restless and hard to notice. It flutters its wings quickly, and that shows its white flanks and white armpits, which is often the moment you realise what you are looking at.

Where it lives

It is common in the understory and mid-levels of humid forest, in both primary and secondary forest. In Costa Rica it reaches only about 900 m elevation, so look for it in the lowlands and foothills.

The Central American subspecies albigula lives on the Caribbean slope, from Honduras through Nicaragua and Costa Rica into Panama. That points to the Caribbean lowlands as the place to search in Costa Rica.

Similar birds

It is the only antwren with white flank patches, so check the flanks. In Costa Rica, the Slaty Antwren is a similar-sized relative.

Names and lore in Costa Rica

Costa Rica, Colombia and Nicaragua use the Spanish name Hormiguerito Flanquiblanco. Honduras uses a similar name, Hormiguerito Flancos Blancos, and a fuller Spanish form, Flanquialbo, is also used.

Status and conservation

The official Costa Rican list marks it as a resident species (R), and its large range keeps it at Least Concern.