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.
Montane White-eye Zosterops poliogastrus is being split into Z. poliogastrus, Z. eurycricotus, Z. kaffensis, Z. kikuyuensis, Z. kululensis, Z. mbuluensis, Z. silvanus and Z. winifredae, following the application of criteria set out by Tobias et al. (2010).
Prior to this taxonomic change, Z. poliogastrus was listed as Least Concern, on the basis that it did not approach the threshold for Vulnerable under any criterion. Z. poliogastrus (as now defined following the taxonomic change) is found in Eritrea, the Ethiopian Highlands south to Addis Ababa and east to Harar; as well as in the mountains of south-east South Sudan, where it can be very common (Fry et al. 2000). Z. kaffensis is found throughout western and south-western Ethiopia, where the pre-split species was described as common at 1,380-3,230 m in evergreen forest (Fry et al. 2000). Z. kikuyuensis is found in the central Kenyan Highland from the Aberdare Mountains, Mount Kenya, Meru District and south to Nairobi. It is very common in some parts of its range (Mount Kenya, Aberdare Mountains and the area around Nairobi) and local elsewhere in its range (van Balen 2016). While the population size and trends for these species have not been quantified it is not thought that they approach the threshold for Vulnerable under any criterion. Therefore it is proposed that they are listed as Least Concern.
Z. eurycricotus is found in northern Tanzania, and is known from the Mount Kilimanjaro region, Arusha, Mount Meru, Essimingor, Lossogonoi and Lolkissale in highland forest (Fry et al. 2000). Z. mbuluensis is found in southern Kenya and northern Tanzania, and is known from highland forest at Namanga and Chyulu Hills, Mount Hanang, Mbulu and Crater Highlands, Mount Ketumbeine and Longido east to the northern Pare Mountains (Frey et al. 2000). Both these species occur at multiple locations*, and while their population sizes have not been quantified, they are unlikely to approach the threshold for Vulnerable, even though declines may be occurring as a result of habitat loss throughout their ranges. We request any comments as to whether the distributions of these species may be considered severely fragmented (see IUCN 2001, 2012), as this may then qualify the species as at least Vulnerable under criterion B. However, in the absence of further information both of these species would not approach the threshold for Vulnerable, and so it is proposed that they be listed as Least Concern.
Z. silvanus is found only in the remaining forest on Taita Hills and Mount Kasigau (BirdLife International 2000). It will use some habitats that may be more disturbed such as forest edge (Mulwa et al. 2000), and there is some protection for the forest on Mount Kisagau and attempts to safeguard the remaining forest in the Taita Hills (BirdLife International 2000), but its habitat is still declining. Surveys in the late 1990s suggested a minimum population of 922 individuals in Taita Hills (Mulwa et al. 2000), which is thought to be declining and becoming severely fragmented as a result of habitat loss. Therefore, given its very small range this species likely qualifies as at least Vulnerable under criteria B1ab(i,ii,iii,v);C2a(i), and probably Endangered under criterion B1ab(i,ii,iii,v).
Z. kulalensis is found only in a very small area of forest and bushland on Mount Kulal in northern Kenya (BirdLife International 2000). It is very common there, possibly the most abundant bird species on the mountain, with an estimated population of c.10,000 mature individuals (Borghesio and Ndang’ang’a 2001). Human activity has led to a thinning of the forest, and this may in fact be beneficial for this species (Borghesio and Ndang’ang’a 2001). The species has a highly restricted range but it is not clear that there are any plausible threats that could cause it to become Critically Endangered or Extinct within a short space of time. It is therefore proposed to list the species as Near Threatened on the basis that it approaches the conditions for listing as Vulnerable under criterion D2.
Z. winifredae is found in Erica heath, and forest clearings and edge in the South Pare Mountains (BirdLife International 2000). It was considered common in 1992, being found in Chome Catchment Forest Reserve and Mwala Forest, as well as potentially Chambogo Catchment Forest Reserve and Kwizu Forest (Collar and Stuart 1985). The population was then estimated to be several thousand birds (Collar and Stuart 1985), but it is unlikely that this number exceeded 10,000 mature individuals given the species’s restricted range. Within its restricted range forests are under threat from clearance particularly for agriculture, grazing, and extraction of wood for fuel (BirdLife International 2000). The population is therefore likely to be declining, and so the species would likely qualify as Vulnerable under criterion C2a(ii).
Comments are invited on these proposed categories and further information would be welcomed.
*Note that the term ‘location’ defines a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present. The size of the location depends on the area covered by the threatening event and may include part of one or many subpopulations. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat (IUCN 2001, 2012).
BirdLife International 2000. Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International.
Borghesio, L. and Ndang’ang’a, P. K. 2001. An avifaunal survey of Mt Kulal, Kenya. Scopus 22: 1-12.
Collar, N. J. and Stuart, S. N. 1985. Threatened birds of Africa and related islands: the ICBP/IUCN Red Data Book. Cambridge , UK: International Council for Bird Preservation, and International Union for Conservation of Nature and Natural Resources.
Fry, C. H., Keith, S. and Urban, E. K. 2000. The Birds of Africa. Vol. VI. Academic Press, London.
IUCN. 2001. IUCN Red List Categories and Criteria: Version 3.1. Gland, Switzerland and Cambridge, UK: IUCN Species Survival Commission.
IUCN. 2012. Guidelines for Application of IUCN Red List Criteria at Regional and National Levels: Version 4.0. Gland, Switzerland and Cambridge, UK: IUCN.
Mulwa, R., Barasa, F., Eshiamwata, G. and Bennun, L. 2000. Population size and ecology of the Taita White-eye Zosterops (poliogaster) silvanus in the forests of the Taita Hills and Mount Kasiagu, Kenya. Abstract of paper to be presented at Pan-African Ornithological Congress 10. Lampala, Uganda.
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.
van Balen, B. 2016. African Montane White-eye (Zosterops poliogastrus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/60223 on 26 September 2016).