Archived 2016 topics: Papyrus Yellow Warbler (Chloropeta gracilirostris) is being moved to genus Calamonastides and split: list Calamonastides gracilirostris and C. bensoni as Vulnerable?

This is part of a consultation on the Red List implications of extensive changes to BirdLife’s taxonomy for passerines

Lynx Edicions and BirdLife International will soon publish the second volume of the HBW-BirdLife Illustrated Checklist of the Birds of the World, building off the Handbook of the Birds of the World series, and BirdLife’s annually updated taxonomic checklist.

The new Checklist will be based on the application of criteria for recognising species limits described by Tobias et al. (2010). Full details of the specific scores and the basis of these for each new taxonomic revision will be provided in the Checklist.

Following publication, an open and transparent mechanism will be established to allow people to comment on the taxonomic revisions or suggest new ones, and provide new information of relevance in order to inform regular updates. We are also actively seeking input via a discussion topic here regarding some potential taxonomic revisions that currently lack sufficient information.

The new Checklist will form the taxonomic basis of BirdLife’s assessments of the status of the world’s birds for the IUCN Red List. The taxonomic changes that will appear in volume 2 of the checklist (for passerines) will begin to be incorporated into the 2016 Red List update, with the remainder to be incorporated into subsequent Red List updates.

Preliminary Red List assessments have been carried out for the newly split or lumped taxa. We are now requesting comments and feedback on these preliminary assessments.

Papyrus Yellow Warbler Chloropeta gracilirostris is being moved to genus Calamonastides and split into C. gracilirostris and C. bensoni, following the application of criteria set out by Tobias et al. (2010).

Prior to this taxonomic change, Papyrus Yellow Warbler was listed as Vulnerable under criterion C2a(i), on the basis that it was believed to have a small and severely fragmented population, which is suspected to be undergoing a continuing decline owing to drainage and human exploitation of its papyrus-swamp habitat (BirdLife International 2016). C. gracilirostris (as now defined following the taxonomic change) is found in papyrus swamps and sometimes other marshy habitat in western Kenya, western Uganda and neighbouring areas of Democratic Republic of Congo, as well as Rwanda, Burundi and adjacent north-west Tanzania (see BirdLife International 2016). 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).

Previous population estimates for the pre-split species of 2,500-9,999 mature individuals may be too low as Maclean et al. (2014) estimated the population size for this species at c. 90,000 adult individuals assuming population densities were equal across the entire range. This may not be the case, but still assuming only 20% occupancy of suitable habitat, the population size is likely to exceed 18,000 mature individuals. 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% and thus this species would warrant listing as Vulnerable A2c+3c+4c.

C. bensoni is found only at Lake Mweru at the mouth of the Luapula River and adjacent papyrus swamps in Zambia and Democratic Republic of Congo (BirdLife International 2016). The population has been estimated at c.5,000 mature individuals (Maclean et al. 2014) assuming population densities were equal across the entire range. While this may not be the case it is provisionally suggested that the population size would fall in the range of 2,500-9,999; though we would welcome any comments or further information regarding this estimate.

The population may be declining as a result of the drainage of papyrus swamps, and the habitat in Zambia has been at risk from fire in the past (Leonard and Beel 1999). 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 of c.21% (80% CI: 10.76-31.97%) (Maclean et al. 2014). Its range is thought as severely fragmented (Maclean et al. 2014) with its Area of Occupancy in 2km grid cells estimated at 516km2 (80% CI: 188-9,320km2) (Maclean et al. 2014), which may be declining. Declines all depend on the assumption that trends between 1984-1987 and 1999-2001 have continued, and we would welcome any further information on more recent trends. In the absence of further information it is proposed that this species be listed as Vulnerable under at least B2ab(i,ii,iii,v);C1+C2a(ii).

Comments are invited on these proposed categories and further information would be welcomed especially regarding potential trends over the past 10 years.

References:

BirdLife International 2016. Species factsheet: Chloropeta gracilirostris. Downloaded from http://www.birdlife.org on 28/09/2016.

Leonard, P. and Beel, C. 1999. Two new resident birds in northern Zambia. Bulletin of the African Bird Club 6(1): 56-57.

Maclean, I. 2006. What constitutes a species? – a conservation problem. BTO News 264: 10-11.

Maclean, I. M. D., Bird, J. P. and Hassall, M. 2014. Papyrus swamp drainage and the conservation status of their avifauna. Wetlands Ecol. Manage.

Maclean, I., Musina, J., Nalianya, N., Mahood, S., Martin, R. and Byuaruhanga, A. 2003. Systematics, distribution and vocalisations of Payrus Yellow Warbler Chloropeta gracilirostrisBulletin of the African Bird Club10(2): 94-100.

Tobias, J. A., Seddon, N., Spottiswoode, C. N., Pilgrim, J. D., Fishpool, L. D. C. and Collar, N. J. 2010. Quantitative criteria for species delimitation. Ibis 152: 724–746.

This entry was posted in Africa, Archive, Taxonomy and tagged , , , , , , , . Bookmark the permalink.

2 Responses to Archived 2016 topics: Papyrus Yellow Warbler (Chloropeta gracilirostris) is being moved to genus Calamonastides and split: list Calamonastides gracilirostris and C. bensoni as Vulnerable?

  1. Michael Mills says:

    Based on the observed (but not quantified) rate of papyrus/wetland clearance in both Uganda and Rwanda (pers. obs.), and how scarce the bird is even in undisturbed papyrus, I suspect that the threat status of gracilirostris is probably Endangered.

  2. James Westrip (BirdLife) says:

    Based on available information, our preliminary proposal for the 2016 Red List would be to currently adopt the proposed classifications outlined in the initial forum discussion.

    There is now a period for further comments until the final deadline of 28 October, after which the recommended categorisations will be put forward to IUCN.

    Please note that we will then only post final recommended categorisations on forum discussions where these differ from those in the initial proposal.

    The final 2016 Red List categories will be published on the BirdLife and IUCN websites in early December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

Comments are closed.