VU
Grauer's Swamp-warbler Bradypterus graueri



Justification

Justification of Red List category

This species is predicted to experience a rapid future population decline resulting from a large range contraction due to climate change. It has therefore been classified as Vulnerable.

Population justification
The density at Kamiranzovu Swamp, Nyungwe, is about 13 birds per ha based on surveys of singing birds; the swamp covers an area of c.25 km2, resulting in an estimate of 33,000 birds at this site alone (A. Plumptre in litt. 2007). Therefore the total population is conservatively inferred to be in the range 20,000-49,000 individuals, roughly equating to 12,000-30,000 mature individuals.

Trend justification
The population is inferred to be in decline owing to the drainage of marshes for agriculture and hydropower, encroachment for mining, and brickmaking (Kahindo et al. 2017). Ayebare et al. (2018) identified this species as being highly at risk of range loss due to climate change, with a suspected decline rate of 40% over three generations.

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). It has also recently been confirmed at Bihinga Marsh, Nyabihu (C. Nsabagasani. in litt. 2021). 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. 2011b). 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 has an area of c.25 km2, resulting in an estimate of 33,000 birds at this site alone (A. Plumptre in litt. 2007). The species's area of habitat may be 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). However, mining may now pose a threat to other wetland sites in its range (Kahindo et al. 2017). 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. 2011b). 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; Ayebare et al. 2018).

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. 2011a). 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. 2011a). 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
Clark, J.

Contributors
Benstead, P., Butynski, T.M., Dowsett-Lemaire, F., Ekstrom, J., Evans, M., Plumptre, A., Shutes, S., Starkey, M., Taylor, J. & Westrip, J.R.S.


Recommended citation
BirdLife International (2023) Species factsheet: Bradypterus graueri. Downloaded from http://datazone.birdlife.org/species/factsheet/grauers-swamp-warbler-bradypterus-graueri on 11/12/2023.
Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://datazone.birdlife.org on 11/12/2023.