EN
Grauer's Swamp-warbler Bradypterus graueri



Justification

Justification of Red List Category
Despite being locally common, this species has a very small and severely fragmented area of occupancy within its small overall range. Many sites are being converted to cultivation or pasture. Thus the species's area of occupancy is declining and, by inference, so is the number of mature individuals. It is therefore classified as Endangered.

Population justification
The density at Kamiranzovu Swamp, Nyungwe, is about 13 birds per ha based on surveys of singing birds; the swamp is c.25km2, resulting in an estimate of 33,000 birds at this site alone (A. Plumptre in litt. 2007). Therefore the total population is conservatively estimated to be somewhere in the range 20,000-49,000 individuals.

Trend justification
The population is suspected to be in decline owing to the drainage of marshes for agriculture and the cutting and burning of marsh vegetation. The likely rate of decline has not been estimated.

Distribution and population

Bradypterus graueri is found in Rwanda, Burundi, eastern Democratic Republic of Congo (DRC) and south-western Uganda. In Rwanda, it occurs in Rugezi Swamp (Vande Weghe 1983) (probably the largest subpopulation), in the marshes between the Virunga volcanos (Vande Weghe 1983), and in Nyungwe (Rugege) Forest (Vande Weghe 1983, Dowsett-Lemaire 1990). In Burundi, in 1984, the national population was estimated at only c.10 pairs, however at least 30 singing birds were estimated from Mwokora, Kibira National Park, in 2011 (Anon. 2011). In the DRC, it is known from at least six locations west of Lakes Edward and Kivu (Chapin 1953, Friedmann and Williams 1968, T. Butynski in litt. 1999). In Uganda, it occurs in Echuya Forest Reserve (the 700 ha Muchuya swamp formerly thought to hold large numbers, but c.50 pairs estimated here by Ellison [2009]) and Bwindi-Impenetrable National Park (c.400 birds) (Davenport et al. 1996, T. Butynski in litt. 1999). The density at Kamiranzovu Swamp, Nyungwe, is about 13 birds per ha based on surveys of singing birds (A. Plumptre in litt. 2007). The swamp is c.25 km2, resulting in an estimate of 33,000 birds at this site alone (A. Plumptre in litt. 2007). The species's total area of occupancy is probably c.200-250 km2 (Arinaitwe 1996, Mwambu 1999).

Ecology

It is found in a wide variety of montane marshes, usually dominated by grass or sedge (Chapin 1953, Vande Weghe 1983, Dowsett-Lemaire 1990, Mwambu 1999). It feeds on small beetles, caterpillars, spiders and small seeds (Urban et al. 1997). It is monogamous and territorial. In Uganda there was some evidence of breeding activity in February-May (Mwambu 1999) and it may breed in March in the eastern DRC (Chapin 1953). At least two nests have been found in Rwanda; one in Rugezi Swamp and the other in Kabatwa Swamp in the Volcanoes National Park (Anon. 2007). The latter was described as a small cup-shaped nest constructed from Poa leptocrada and other sedges, and perched in foliage 35 cm above the ground (C. Nsabagasani per Anon. 2007).

Threats

Rugezi Swamp was formerly unprotected and was being encroached by agriculture and progressively degraded by cutting and burning of vegetation during the dry season (Kanyamibwa 2001). However, it is now better protected as it supplies water to the hydroelectric dam at Lake Bulera, which provides power to Kilagi (A. Plumptre in litt. 2007). Following power cuts in 2005-2006, the government has moved people away from the swamp to ensure the protection of this water supply (A. Plumptre in litt. 2007). Marsh habitat in Nyungwe Forest was formerly threatened by gold-mining, but by 1989 this threat had disappeared (Dowsett-Lemaire 1990). In DRC, many parts of the range are densely settled and many montane marshes have been drained for cultivation or pasture (Sarmiento and Butynski 1997). In Burundi habitat at Mwokora is threatened by cutting for mats and thatching, and other valley swamps in Kibira National Park are threatened by encroaching agriculture (Anon. 2011). A climate change modelling exercise identified the species as one of the Albertine Rift endemics likely to be most severely affected by climate change (Anon. 2009).

Conservation actions

Conservation Actions Underway
In Uganda, Bwindi-Impenetrable National Park is well protected, and since 2004 the RSPB and NatureUganda have been working to conserve Echuya Forest Reserve (Arinaitwe 1996, T. Butynski in litt. 1999, Mwambu 1999, Anon. 2011). Work at Echuya has included development of a management plan, Collaborative Forest Management arrangements, planting of tree and bamboo seedlings to reduce pressure on the forest, income-generating activities to improve local livelihoods, environmental education, local empowerment, training and capacity-building, and watershed management (Anon. 2011). In Rwanda, reports suggest that Nyungwe Forest Reserve has suffered little encroachment recently, due to human emigration following conflict in the area (F. Dowsett-Lemaire in litt. 2000). In DRC, the only protected swamps are in Kahuzi-Biéga National Park and on Mt Tshiaberimu, and the former area is not secure (Hall et al. 1998). Since July 2006, a team have been monitoring the species in the Volcanoes National Park, Rwanda (Anon. 2007). An international and two national (Uganda and Rwanda) action plans have been developed for the species (Anon. 2009).

Conservation Actions Proposed
Conduct surveys to assess the species's total population size. Monitor the species's population across its range. Monitor habitat trends across the species's range. Ensure the continued protection of Rugezi Swamp in Rwanda (Hall et al. 1998). Continue to assess the current status of the main swamp areas in Nyungwe Forest. Confirm its absence from the Itombwe massif (T. Butynski in litt. 1999). Continue to search for nests and carry out research into its breeding biology in order to aid surveys and habitat management (P.K. Ndang'ang'a per Anon. 2007).

Identification

16 cm. Medium-sized, skulking, drab warbler. Dark brown overall. Mottling on throat. Long, broad tail has slight russet tinge. Similar spp. White-winged Scrub-Warbler B. carpalis has white in wings and pale underparts. African Bush-Warbler B. baboecala is smaller and paler. However, these species rarely, if ever, share the same marshes. Voice Fast trill, preceded (and sometimes followed) by a few loud chup notes. Hints Very vocal, singing in full view on top of stems, sometimes in duet (Dowsett-Lemaire 1990), or during short display-flight accompanied by wing-whirring and fanned, lowered tail.

Acknowledgements

Text account compilers
Benstead, P., Ekstrom, J., Evans, M., Shutes, S., Starkey, M., Taylor, J. & Westrip, J.

Contributors
Butynski, T.M., Dowsett-Lemaire, F. & Plumptre, A.


Recommended citation
BirdLife International (2019) Species factsheet: Bradypterus graueri. Downloaded from http://www.birdlife.org on 24/05/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 24/05/2019.