Yellow-bellied Tyrannulet

How to find it

Learn the song first: a fast series of high, nasal notes that drop in pitch. Because it usually stays high in the canopy, listening is the easiest way to locate it. Then search the treetops where the sound comes from. Keep to lower elevations, since in Costa Rica it only reaches about 600 m. Scan leaves and twigs from the mid-levels up for a tiny bird picking food off foliage, and give each calling bird time.

How to recognise it

This is a tiny flycatcher, about 8 to 9 cm long, weighing only about 7 to 8 grams. Look for these marks in plain order:

- a gray crown

- a white eyebrow that runs onto the forehead

- olive upperparts

- bright yellow underparts with faint olive streaks on the breast and flanks

- a black bill, slightly arched on top, and a brown eye

Among small flycatchers in its range it stands out for the all-yellow underparts, the clear white eyebrow, a tiny bill and a short tail. Males and females look alike. Juveniles have a brownish tinge on the crown and back and paler yellow underparts than adults.

Behaviour and diet

It feeds almost entirely on arthropods. It forages alone or in pairs, from mid-levels to the canopy inside forest and lower at forest edges. It picks prey off leaves, twigs and stems while perched, and sometimes joins mixed flocks.

Its manner is much like a warbler or a vireo, a useful clue when a tiny canopy bird does not act like a typical flycatcher.

Where it lives

It lives in the interior and edges of humid evergreen forest and older secondary forest. It also uses plantations, gardens with tall tree and tall semi-deciduous scrub.

In Costa Rica it only reaches about 600 m elevation, while elsewhere in its range it goes up to about 1,500 m. It occurs on the Caribbean slope into northern Costa Rica. On the Pacific side it occurs from central Costa Rica south into western Panama.

Similar birds

It was once treated as the same species as the Brown-capped Tyrannulet. The two differ in plumage, voice and habitat, and they apparently do not interbreed where their ranges overlap in Costa Rica. A Costa Rica guide suggests that the Yellow-bellied, Brown-capped, Rough-legged and Rufous-browed Tyrannulets have field marks that make them easier to identify than the four common tyrannulets.

Names and lore in Costa Rica

Costa Ricans call it Mosquerito Cejiblanco. Other countries use different Spanish names: cejigrís in Honduras, tiranolete ventriamarillo in Panama, and mosquerito enano or mosquero ceja blanca in Mexico. Nicaragua uses mosquiterito cejiblanco, and mosquerito ventriamarillo serves as the general name.

Status and conservation

The official Costa Rican bird list gives it resident status (R), and the IUCN rates it Least Concern.

Photography tips

Most tyrannulets in Costa Rica live in the canopy and rarely stay still. One Costa Rica birder says this makes them very hard to photograph, even with a digiscoping set-up. The genus Ornithion typically stays high in the canopy and is very tough to photograph, so treat a clear view as a bonus.