NT
Dapple-throat Arcanator orostruthus



Justification

Justification of Red List Category
This species is suspected to have a small population, and is undergoing a continued decline. It is therefore listed as Near Threatened.

Population justification
The population in Mozambique was estimated by Dowsett-Lemaire (2010) to be 600-1,000 mature individuals on Mt Namuli, and up to 200 mature individuals on Mt Mabu. Since those surveys, large swathes of forest has been lost (J. Timberlake in litt. 2020), and the population in Mozambique is now likely to be <1,000 total individuals (B. Phalan in litt. 2020). This species was recently discovered on the Njesi Plateau in Mozambique (Jones et al. 2017), with the population there likely to be smaller than that on Namuli (B. Phalan in litt. 2020). The total population in the East Usambaras was considered to possibly only number a few pairs (Borghesio et al. 2008), and is still considered to be very rare (Neate-Clegg et al. 2021). The species in the Udzungwa Mountains may have undergone substantial declines owing to the effect of forest loss and degradation on its localised population (B. Phalan in litt. 2020), and the population may therefore be very small. In the absence of more conclusive data, the population size is tentatively suspected to fall into the band of 1,000-2,499 mature individuals. It is also tentatively assumed, based on available data, that the largest subpopulation contains <1,000 mature individuals.

Trend justification
The species's population is inferred to be declining in line with the fragmentation and degradation of mid-elevation forests within its range. Due to habitat loss (Dowsett-Lemaire, 2010; Timberlake, 2017), it is suspected to be declining at a rate of 10-20% over three generations (10.5 years [Bird et al. 2020]).

Distribution and population

Arcanator orostruthus is found on Mt Namuli, Mt Mabu, and the Njesi Plateau in Mozambique and in the East Usambara Mountains and Udzungwa Mountains in Tanzania. It may also occur in the southern forests (c.1,220 ha) between Mt Namuli and Gurue (Ryan et al. 1999), although the forest remnants here may persist at too low an altitude (below 1,400m) for this species (F. Dowsett-Lemaire, 2020, pers. comm.). It is not known from Mt Mulanje (Dowsett-Lemaire 2010), however in November 2016, this species was discovered on the Njesi Plateau, Mozambique (Jones et al. 2017; Jones et al. 2020).


Ecology

It inhabits wet montane forest, especially near streams and in shrubby areas (Collar and Robson, 2020), and at elevations between 900 and 1,800 m (Dinesen et al. 2001, Dowsett-Lemaire 2010, Collar and Robson 2020). It prefers 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

The loss of Afromontane forest due to potato cash crops on Mt Namuli since 2007 is extensive. An estimated 10% has been lost from the greater Manho Forest, and up to 80% has been lost in the Nivolo Valley, below Mt Pesse (Timberlake, 2017). Despite the seed bank, there is little evidence of natural forest regeneration, owing to frequent wild fires (Timberlake, 2017). The forest at Mt Mabu (where the species is rarer) has remained relatively undisturbed (F. Dowsett-Lemaire, 2020, pers. comm.). 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 (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). Community-based forest management schemes are also being explored in the East Usambaras with the aim of involving local communities in conserving and restocking forests (Rantalla et al. 2012).

Conservation Actions Proposed
Stop further forest clearance, on Mt Namuli, and focus agricultural improvement efforts on fields below 1500m. Establish controls on wild fires to help the potential regeneration of forest vegetation (Timberlake, 2017). Provide economic incentives to cultivate more eco-compatible crops, such as coffee or cloves, rather than tea (Borghesio et al. 2008).


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
Clark, J.

Contributors
Dinesen, L., Ekstrom, J., Evans, M., Hermes, C., Moyer, D., Parker, V., Shutes, S., Starkey, M., Symes, A., Taylor, J., Timberlake, J.R. & Westrip, J.R.S.


Recommended citation
BirdLife International (2022) Species factsheet: Arcanator orostruthus. Downloaded from http://www.birdlife.org on 08/08/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 08/08/2022.