Nesotriccus ridgwayi 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Aves Passeriformes Tyrannidae

Scientific Name: Nesotriccus ridgwayi Townsend, 1895
Common Name(s):
English Cocos Flycatcher
Taxonomic Source(s): del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A., Fishpool, L.D.C., Boesman, P. and Kirwan, G.M. 2016. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Volume 2: Passerines. Lynx Edicions and BirdLife International, Barcelona, Spain and Cambridge, UK.
Identification information: 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.

Assessment Information [top]

Red List Category & Criteria: Vulnerable D2 ver 3.1
Year Published: 2016
Date Assessed: 2016-10-01
Assessor(s): BirdLife International
Reviewer(s): Butchart, S. & Symes, A.
Contributor(s): Stiles, F.
Facilitator/Compiler(s): Isherwood, I., Mahood, S., Pilgrim, J., Pople, R., Sharpe, C.J.
This species is listed as Vulnerable because it has a very 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.

Previously published Red List assessments:

Geographic Range [top]

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

Countries occurrence:
Costa Rica
Additional data:
Continuing decline in area of occupancy (AOO):Unknown
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:30
Continuing decline in extent of occurrence (EOO):UnknownExtreme fluctuations in extent of occurrence (EOO):No
Number of Locations:1Continuing decline in number of locations:Unknown
Extreme fluctuations in the number of locations:No
Upper elevation limit (metres):570
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population: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.
Current Population Trend:Stable
Additional data:
Number of mature individuals:6000-15000Continuing decline of mature individuals:Unknown
Extreme fluctuations:NoPopulation severely fragmented:No
No. of subpopulations:1Continuing decline in subpopulations:Unknown
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:Yes
No. of individuals in largest subpopulation:100

Habitat and Ecology [top]

Habitat and Ecology: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.

Systems:Terrestrial; Freshwater
Continuing decline in area, extent and/or quality of habitat:Unknown
Generation Length (years):3.6
Movement patterns:Not a Migrant

Threats [top]

Major Threat(s): 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 [top]

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.

Citation: BirdLife International. 2016. Nesotriccus ridgwayi. The IUCN Red List of Threatened Species 2016: e.T22699191A93718612. . Downloaded on 22 January 2018.
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