Justification of Red List Category
This species is listed as Vulnerable because it is believed to have undergone and continues to undergo a rapid decline as a result of extensive habitat loss.
Maclean et al. (2014) estimated the population to be 90,000 adults, assuming 100% occupancy of habitat. Assuming instead that only a proportion (20%) of its habitat is inhabited then the population size may in fact be nearer 18,000 mature individuals. This would fit in the range of 10,000-19,999 mature individuals.
This species's population is suspected to be declining in line with habitat loss and degradation within its range. Rates of decline in this species have been estimated by assuming that the relationship between habitat variables and density/occurrence were the same between data from 1999-2001 compared to 1984-1987 (Maclean et al. 2014). This gave an estimate of a decline over 3 generations of c.35% (80% CI: 15.21-40.15%) in the Albertine Rift population (Maclean et al. 2014). For the Kenyan population, declines were estimated at c.92% (80% CI: 42.40-96.07%), and future declines in this species were stated as likely to be >80% (Maclean et al. 2014). While declines over the past 3 generations may not be the same as that over the modelled time period, declines over 3 generations are still suspected to have been large and ongoing but the global rate of decline is unlikely to exceed 50% over 3 generations. However, the decline would fall in the range of 30-49%.
C. gracilirostris has a severely fragmented range in the Great Lakes region of Africa. The nominate race occurs in western Kenya (Nasirwa and Njoroge 1997), western Uganda (Chapin 1953, J. Lindsell in litt. 1999, D. Pomeroy in litt. 1999) and adjacent areas of Democratic Republic of Congo (DRC) (Chapin 1953), in Rwanda and Burundi extending just into north-west Tanzania (Vande weghe 1981), and it may also occur in unsurveyed areas of west and north-west Tanzania (N. Baker in litt. 1999).
It is found mainly in papyrus-swamps but occasionally in other marshy habitats, especially reeds (Chapin 1953, Nasirwa and Njoroge 1997, Leonard and Beel 1999, P. Leonard in litt. 1999). Its breeding ecology is unknown, but individuals of the nominate race have been recorded in breeding condition between April and June (Chapin 1953, Britton and Harper 1969).
Its wetland sites are threatened by drainage for the cultivation of crops (Maclean et al. 2003), such as rice (Maclean 2006), and dairy farming (Maclean et al. 2003). Ongoing drainage of Yala Swamp, the most important site in Kenya, will reduce the national area of occupancy by about a third, despite the poor agricultural performance of already drained areas (L. Bennun in litt. 1999). All other papyrus-swamps in Kenya are threatened both by human pressure, owing to an expanding population, and by man-made ecological changes in Lake Victoria itself, including infestation by water hyacinth Eichhornia crassipes (L. Bennun in litt. 1999). This latter problem has caused the collapse of the Lake Victoria fisheries, forcing local people to seek other sources of income (Maclean et al. 2003). Such problems, and a shortage of productive land, create pressure through the encroachment of agriculture and over-harvesting of papyrus for use as fuel or in local crafts (Maclean et al. 2003). Similar problems may affect it in Uganda. In Rwanda, its wetlands are being progressively degraded through cutting and burning of papyrus in the dry season (Kanyamibwa 2001) and the situation is probably similar in Burundi, while its current status in the DRC is unknown. One site in Kenya is threatened by the expansion of a nearby town (Maclean 2006).
Conservation Actions Underway
Its ecology is being studied at Yala Swamp in Kenya (Nasirwa et al. 2000). In Uganda, there is a substantial area of papyrus within Lake Mburo National Park and part of Lake George is within Queen Elizabeth National Park. Lakes Edward and Bunyonyi, and the Butiaba area on Lake Albert, may be suitable for community-based conservation projects (J. Lindsell in litt. 1999).
14 cm. Medium-sized warbler of swamps. Warm olive-brown to russet above, especially on tail. Yellow below, washed with olive across breast and flanks. Similar spp. Other warblers in swamps are brown, grey and white, rather than yellow-and-green. Voice Melodious, liquid warblings. Hints Most often detected by voice. Most accessible site is at Lake Bunyonyi, Uganda. It occurs singly or in pairs, foraging in the mid and upper levels of papyrus for tiny insects, and perhaps tending to feed over water (Chapin 1953).
Text account compilers
Ekstrom, J., Evans, M., Pilgrim, J., Shutes, S., Starkey, M., Symes, A., Taylor, J. & Westrip, J.
Baker, N., Bennun, L., Leonard, P., Lindsell, J. & Pomeroy, D.
BirdLife International (2019) Species factsheet: Calamonastides gracilirostris. Downloaded from http://www.birdlife.org on 16/02/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 16/02/2019.