VU
Dapple-throat Arcanator orostruthus



Justification

Justification of Red List Category
This species has a small, disjunct range, within much of which its habitat is either currently, or probably soon will be, declining in both extent and quality, leading to increasing fragmentation of its distribution (Collar and Stuart 1985). It is therefore considered Vulnerable.

Population justification
The population size is preliminarily estimated to fall into the band 10,000-19,999 individuals. This equates to 6,667-13,333 mature individuals, rounded here to 6,000-15,000 mature individuals. However, the total population may be smaller, as it is apparently common in only a few locations in the Udzungwas (L. A. Hansen per J. Fjeldså in litt. 2012).

Trend justification
The species's population is suspected to be declining in line with the fragmentation and degradation of mid-elevation forests within its range. The likely rate of decline, however, has not been estimated.

Distribution and population

Modulatrix orostruthus is found on Mt Namuli and Mt Mabu in Mozambique and in the East Usambara Mountains and Udzungwa Mountains in Tanzania. In Mozambique, the nominate subspecies is relatively common, with densities of up to 2-3 singing birds/ha reported in Ukalini Forest (c.80 ha) (Ryan et al. 1999), but rare on Mt Mabu (Dowsett-Lemaire 2010). It may also occur in the southern forests (c.1,220 ha) between Mt Namuli and Gurue (Ryan et al. 1999), but is not known from Mt Mulanje (Dowsett-Lemaire 2010). The population in Manho and Ukalini on Mt Namuli might be 300-500 pairs (assuming densities of 3-5 pairs /10 ha), and there may be a few dozen-100 pairs on Mt Mabu (Dowsett-Lemaire 2010). In the East Usambaras, subspecies amani had a population between several hundred and several thousand in 1990, possibly nearer the former (Newmark 1991), however surveys of the southern East Usambaras in 2006 recorded only one individual; although numbers may have been underestimated, the total population in the East Usambaras was considered to possibly only number a few pairs (Borghesio et al. 2008). Subspecies sanjei is uncommon to fairly common in seven forested areas on the Udzungwa escarpment (D. C. Moyer in litt. 1999, L. Dinesen in litt. 2007, Butynski in press), e.g. at Uhafiwa, where the density was up to 31 pairs/km2 in 1990 (Dinesen et al. 1993). The population on the Udzungwa escarpment alone was estimated at probably over 10,000 individuals (L. Dinesen in litt. 2007), however this may be optimistic (L. A. Hansen per J. Fjeldså in litt. 2012). The overall population is thought to be declining.

Ecology

It inhabits wet montane forest at mid-elevations (mostly 1,300-1,700 m [Butynski in press], but there have been a few observations at 1,200m in Ukami [Dinesen et al. 2001]), preferring closed-canopy areas with a dense growth of wild ginger (Zingiberaceae) and saplings on the ground. Here it moves through corridors of thick growth around light gaps and along streams, foraging for insects in the leaf-litter. At Namuli it is confined to forest above 1,500 m, and occurs up to 1,870 m in Ukalini and Manho, while on Mabu it is rare and local above 1,380 m (Dowsett-Lemaire 2010).

Threats

Forest on Mt Namuli is, at present, largely intact, but the lower slopes are now densely settled. Encroachment is now taking place above 1,500 m, with two small areas of Manho Forest cleared for potato crops in 2007 and many more cleared for gardens over the following year (Dowsett-Lemaire 2010), as well as forest being cleared for livestock grazing (J. Timberlake in litt. 2016). Timber extraction of Faurea wentzeliana takes place in both Ukalini and Manho forests, creating gaps in the canopy (Dowsett-Lemaire 2010). The forest at Mt Mabu (where the species is rarer) is under less pressure as the human population in the foothills is smaller and more scattered: dry season bush fires are a current threat to the forest here (Dowsett-Lemaire 2010), but but they may be less of a threat here than in other forests in the region (J. Timberlake in litt. 2016). In the Usambaras, the large human population is putting increasing pressure on forests both outside and within forest reserves, and forest is now highly fragmented (Newmark 1991); the species may be close to extinction here (J. Fjeldså in litt. 2012). Forest in several areas of the Udzungwa Mountains is still being cleared for timber and agriculture, however the rate of loss has slowed thanks to improved management, and there is some regeneration in places. Nevertheless, core (mature forest) habitat continues to decrease (J. Fjeldså in litt. 2012).

Conservation actions

Conservation Actions Underway
Amani Nature Reserve in the East Usambaras has been gazetted and covers 84 km2, including forest owned by private tea companies. Two conservation and development projects in the East Usambaras are working to increase the amount of forest in protected areas, including all lowland remnants (Tye 1993). The subspecies sanjei occurs within several protected areas, although these are under pressure from logging and burning (L. Dinesen in litt. 2007). In the Udzungwa Mountains community-based forest management has resulted in the exclusion of commercial logging, although some cutting and clearing for bean-fields and marijuana continues (J. Fjeldså in litt. 2012).

Conservation Actions Proposed
Conduct surveys to obtain an up-to-date population estimate. Once a baseline population estimate has been obtained, conduct regular surveys to monitor population trends. Monitor rates of forest clearance and degradation at known sites, and prevent commercial logging from spreading through the species's range. Establish whether it occurs in the remote southern forests of Mt Namuli and, if so, designate as a core wilderness area (Ryan et al. 1999). Survey other sections of forest at Mabu, and other peaks near Namuli with forest patches, and Mt Chiperone (Dowsett-Lemaire 2010). Assess possibility of ecotourism-based conservation programme involving local people at Ukalini Forest on Mt Namuli (Ryan et al. 1999).

Identification

17 cm. Medium-sized, drab robin of forest. Olive-brown upperparts. Paler, lemon yellow, broadly spotted underparts. Slender bill has pale base. Rusty tinge on outertail. Similar spp. Greenbuls Phyllastrephus spp. in same habitat have plain underparts and are less terrestrial; Spot-throat M. stictigula has spots confined to throat and is rich chestnut. Voice Clear, flutey, whistled hooo ree, also many other varied whistles and phrases, some very oriole-like. Hints Terrestrial. Furtive and inveterate skulker of forest-tangles. Common on Mt Namuli, Mozambique, and Udzungwa Mountains, Tanzania.

Acknowledgements

Text account compilers
Ekstrom, J., Evans, M., Shutes, S., Starkey, M., Symes, A., Taylor, J. & Westrip, J.

Contributors
Dinesen, L., Moyer, D., Parker, V. & Timberlake, J.


Recommended citation
BirdLife International (2020) Species factsheet: Arcanator orostruthus. Downloaded from http://www.birdlife.org on 24/09/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 24/09/2020.