Southern Beardless Tyrannulet

The Southern Beardless Tyrannulet, scientifically known as Camptostoma obsoletum, is a diminutive member of the tyrant flycatcher family. This avian species is characterized by its modest size, measuring a mere 10.2 cm in length and weighing approximately 7.5 grams. Its appearance is somewhat reminiscent of the tiny Yellow-bellied Elaenia, with a dark brown or grey head adorned with an erectile crest and a pale supercilium. The upperparts display a grey-green hue that lightens towards the rump, while the wings are brown with a touch of yellow feather-edging and two wing bars that may vary in color from whitish to yellowish or cinnamon. The tail, often seen held cocked, is brown, and the underparts range from a grey throat to a yellowish breast and a yellow abdomen. The bill is predominantly black, with the base of the lower mandible showing a paler shade.

Identification Tips

When identifying the Southern Beardless Tyrannulet, look for the pale supercilium and the erectile crest on the head. The wing bars are a key feature, appearing brighter than those of its close relative, the Northern Beardless Tyrannulet. The tail behavior is also distinctive, as it is frequently held in a cocked position.

Habitat

This species thrives in a variety of environments, including light forests, cultivated areas, gardens with trees, and the dry cerrado savanna.

Distribution

The Southern Beardless Tyrannulet has a broad range, breeding from Costa Rica through South America to the southern reaches of Paraguay, Bolivia, and Argentina.

Behaviour

These birds are known for their active demeanor, feeding on insects, spiders, and berries in a manner akin to vireos or warblers. They employ sally flights to snatch prey from the air or plants, or they may glean directly from vegetation. They are also known to consume fruit, such as that from the Alchornea glandulosa, either while perched or in hovering flight. This species is known to aggressively mob small predators like the Ferruginous Pygmy Owl and tends to be solitary outside of the breeding season, rarely joining mixed-species feeding flocks.

Song & calls

The Southern Beardless Tyrannulet's call is a loud, whistled "TLEEE-tee-tee-tee." During courtship, the birds exhibit an excited mix of this call with a churring "pee-chrrr-pee-chrrr," accompanied by raised crests and tail flicking.

Breeding

The nest of the Southern Beardless Tyrannulet is a domed structure with a side entrance, constructed from plant fiber or leaves. It is strategically placed near a wasp nest in a tree fork, likely for predator deterrence. The typical clutch consists of two white eggs, speckled with rufous and lilac, particularly at the larger end. The female incubates the eggs for 14-15 days until hatching, followed by a fledging period of 17 days.

Similar Species

The Northern Beardless Tyrannulet (C. imberbe) is the species most similar in appearance, but it can be distinguished by its less vibrant wing bars. The two species' ranges overlap in central Costa Rica, yet they do not interbreed.

Diet and Feeding

The diet of the Southern Beardless Tyrannulet includes insects, spiders, and berries. They are adept at capturing animal prey in flight or from plants and are also known to feed on fruit, which they may pick while perched or in flight.

Conservation status

The IUCN has classified the Southern Beardless Tyrannulet as a species of Least Concern, due to its extensive range and presumably large population.