Justification of Red List Category
The species appears to have a small range which is severely fragmented and continuing to decline in extent, owing to widespread destruction and degradation of its forest habitat. The total population size is unknown but could be small, given the species's apparently very patchy distribution within its range. At present the species is treated as Vulnerable until improved information on its population and distribution becomes available.
The population size is preliminarily estimated to fall into the band 2,500-9,999 individuals. This equates to 1,667-6,666 mature individuals, rounded here to 1,500-7,000 mature individuals.
The species's population is suspected to be declining in line with the clearance and degradation of lowland rainforest in eastern Madagascar. The likely rate of decline, however, has not been estimated.
Bernieria tenebrosa is found only in lowland rainforest in eastern Madagascar, where it is apparently extremely scarce (ZICOMA 1999). The species has been widely misidentified and only recently have the key identification criteria been elucidated (Morris and Hawkins 1998). Recent records have been from Marojejy (775 m), Betampona Strict Nature Reserve (below 600 m) and Zahamena (c.400 m), but it is probably present in all large blocks of suitable habitat, while records from Masoala peninsula, Ranomafana National Park and Analamazaotra Special Reserve require confirmation (ZICOMA 1999, Britt et al. 2003, Hawkins and Sartai 2013). If many apparently spurious reports from Ranomafana and Perinet-Analamazaotra are discounted, it has the most restricted range of the eastern Malagasy rainforest species (ZICOMA 1999). Specimens are known from the central-east (Forêt Sihanaka, near Zahamena, and Mantadia [ZICOMA 1999], as well as Betaolona Forest and Lakato Forest near Moramanga [Hawkins and Sartai 2013]). During inventories of protected areas at Andringitra, Anjanaharibe-South, Andohahela and Marojejy, the species has been recorded only once and never mist-netted, despite around 10 months of survey effort and substantial mist-netting effort (ZICOMA 1999).
This still-mysterious species is found in the understorey of both lowland and mid-altitude (up to 950 m) undisturbed, humid, evergreen forest. It forages for small insects, larvae and small spiders, both on the ground and in low shrubs, while it may avoid dense undergrowth(Randriamanindry 1995, Morris and Hawkins 1998). It often occurs with other ground or low-understorey species, and has been observed recently in mixed-species foraging flocks, where there were usually fewer B. tenebrosa than Spectacled Tetraka B. zosterops or Common Tetraka B. madagascariensis (Randriamanindry 1995, Morris and Hawkins 1998).
Its habitat is being reduced in extent, the principal threat coming from slash-and-burn cultivation by subsistence farmers, which results in progressively more degraded regrowth and leads eventually to bracken-covered areas or grassland (Du Puy and Moat 1996). Much of the eastern coastal plain has either already been cleared or is covered by highly degraded forest (Jenkins 1987), remaining habitat is under pressure from the increasing human population (Jenkins 1987), and commercial logging is an additional threat in some areas (A.F.A. Hawkins in litt. 1995). If present trends continue, the remaining forest will disappear within decades (Du Puy and Moat 1996).
Conservation Actions Underway
This species is known from only three eastern Malagasy IBAs (ZICOMA 1999), including the following protected areas: Marojejy National Park, Masoala National Park, Zahamena National Park (Morris and Hawkins 1998).
14-15 cm. Small, rotund, terrestrial babbler-like bird. Dull dark earth-brown upperparts, with no green or yellow. Bright yellow eye-ring and loral streak to eye, and oval patch on throat. Breast similar dark brown to upperparts, belly paler. Legs stout. Bill and tail rather short. Bill mostly pale pink; pinkish-grey legs. Similar spp. From other Malagasy greenbuls by largely terrestrial habits, dark upper- and underparts, short tail, narrower yellow eye-ring and throat patch, and stronger legs. Hints Hops along ground in lowland rainforest, often in rather open areas.
Text account compilers
Ekstrom, J., Evans, M., Shutes, S., Starkey, M., Symes, A., Taylor, J. & Westrip, J.
Hawkins, F., Lambert, F., Rabenandrasana, M. & Schulenberg, T.
BirdLife International (2019) Species factsheet: Crossleyia tenebrosa. Downloaded from http://www.birdlife.org on 24/03/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 24/03/2019.