Justification of Red List Category
This species qualifies as Vulnerable owing to its small and declining range. The size of the range is small enough to qualify as Endangered, but it is only Vulnerable because recent surveys have found the species at nine locations.
The population is estimated to number 2,500-9,999 individuals based on an assessment of known records, descriptions of abundance and range size. This is consistent with recorded population density estimates for congeners or close relatives with a similar body size, and the fact that only a proportion of the estimated Extent of Occurrence is likely to be occupied. This estimate is equivalent to 1,667-6,666 mature individuals, rounded here to 1,500-7,000 mature individuals.
There are no new data on population trends; however, the species is suspected to be suffering a slow decline, owing to habitat degradation. Large-scale habitat modification has taken place within the Uxpanapa municipality which lies in the heart of the species's range (A. Townsend Peterson in litt. 2016). Evidence to quantify the extent of the species's declines may result in uplisting the species to a higher threat category.
This species has a restricted range in easternmost Veracruz (six sites in the Uxpanapa region, at the mid-point of the Isthmus of Tehuantepec), with records from one site in west Chiapas, and two in east Oaxaca, south Mexico (Gomez de Silva 1997). The total extent of its range was initially estimated at 4,800-4,900 km2, within which it is fairly common but local (Howell and Webb 1995a, Gomez de Silva 1997). However, further mapping indicates that the known range is likely to be considerably smaller. In 1992, a crude density estimate of c.20 birds/km2 was calculated at El Ocote in Chiapas (Atkinson et al. 1993).
It is restricted to limestone outcrops in the shade of primary lowland evergreen forest, mainly at 75-800 m (Atkinson et al. 1993, Howell and Webb 1995a, Gomez de Silva 1997). This habitat is naturally patchy, with outcrops occurring every c.4 km2 in the west and central parts of the Uxpanapa region (Gomez de Silva 1997). Fortunately, it seems able to survive in patches of forest as small as 8 ha (Gomez de Silva 1997). It gleans invertebrates from the lichen-covered surface of the limestone and in the cracks and crevices of boulders (Atkinson et al. 1993).
Settlement and cattle-ranching following road-building have fragmented forests within its range (Atkinson et al. 1993). Although limestone outcrops are generally not suitable for ranching, deforestation has left them isolated and threatened by firewood extraction (Atkinson et al. 1993, Gomez de Silva 1997). This has important implications since such small birds with rounded wings are (predictably) poor dispersers (Atkinson et al. 1993, Gomez de Silva 1997). The Uxpanapa/Chimalapas region has seen large-scale habitat modification in recent decades which may have impacted on the species (A. Townsend Peterson in litt. 2016).
Conservation Actions Underway
It occurs in Selva El Ocote Special Biosphere Reserve, but there is very little suitable habitat within this protected area (Gomez de Silva 1997). An important area of habitat is within the proposed Chimalapas-Uxpanapa Biosphere Reserve (Whittingham and Atkinson 1996). The species is included on the 'Watch List' of the State of North America's Birds as a species of high conservation concern (NABCI 2016).
16 cm. Long-billed, brown-and-white wren. Long blackish bill, orange basally on lower mandible. Grey lores. Rich brown upperparts, barred lightly black on wings. Whitish throat and upper breast becoming grey on lower breast. Faint, dusky scalloping on chest. Dark sooty-brown on sides and flanks. Dusky grey-brown undertail-coverts. White scallops on belly with dark subterminal crescents. Voice Thin nasal iihn in steady series or pairs.
Text account compilers
Sharpe, C.J., Wheatley, H., Pople, R., Mahood, S., Ashpole, J, Isherwood, I., Capper, D.
Townsend Peterson, A., Morales, J., Gomez de Silva, H.
BirdLife International (2020) Species factsheet: Hylorchilus navai. Downloaded from http://www.birdlife.org on 13/07/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 13/07/2020.