Cocos Flycatcher Nesotriccus ridgwayi


Justification of Red List Category
This species is listed as Vulnerable because it has an extremely small range. Introduced herbivores are degrading habitat within its range, but it appears to tolerate some habitat modification and there is (as yet) no evidence of a decline in range or population. If habitat degradation was to intensify, the species could quickly qualify for a higher threat category.

Population justification
The population has been estimated at several tens of thousands of individuals (del Hoyo et al. 2004), but has conservatively been placed in the range band for 10,000-19,999 individuals. This equates to 6,667-13,333 mature individuals, rounded here to 6,000-15,000 mature individuals.

Trend justification
Introduced herbivores are degrading habitat within the species's range, but it appears to tolerate some habitat modification and there is (as yet) no evidence of a decline in its range or population. It is therefore suspected to be stable.

Distribution and population

Nesotriccus ridgwayi is common throughout Cocos Island, c.500 km off the coast of Costa Rica.


It occurs in most habitats from sea-level to the highest hills, including the upper understorey and lower canopy of forests (Stiles and Skutch 1989), Hibiscus scrub, Annona swamp, and wooded ravines. It is regularly observed in second growth (Stiles and Skutch 1989), but degraded habitat may not sustain the species through its life-cycle. The diet consists of insects and, at least seasonally, fruits (Sherry 1985). Breeding probably takes place between January and May.


Rats and cats are potential predators, and feral deer, pigs and goats graze suitable habitat. Pigs especially devastate the lower strata and understorey of native forests and inhibit forest regeneration (Sherry 1985; F. G. Stiles in litt. 1999). On many other islands, this combination of feral mammals has caused the extinction of numerous endemic plant and animal species. There is also low-level disturbance from increasing tourism (Sherry 1985).

Conservation actions

Conservation Actions Underway
Cocos has been designated as a national park, but no substantive measures have been taken to reduce populations of introduced mammals (F. G. Stiles in litt. 1999).

Conservation Actions Proposed
Estimate the population. Study the impact of introduced mammals. Eradicate introduced mammals where feasible.


13 cm. Greyish flycatcher with rather long bill. Greyish-olive to dark brownish-olive above. Faint, dull buffy eyebrow. Dusky wings with two wing-bars and buffy edges to wing feathers. Pale greyish-buff to pale yellowish underparts. Brownish to olive wash to breast. Slender, dusky bill with pale horn lower mandible. Immature browner with tawny wing-bars and eyebrow. Voice Dry, descending and accelerating trill.


Text account compilers
Everest, J.

Isherwood, I., Mahood, S., Pilgrim, J., Pople, R., Sharpe, C.J. & Stiles, F.G.

Recommended citation
BirdLife International (2022) Species factsheet: Nesotriccus ridgwayi. Downloaded from on 30/06/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from on 30/06/2022.