This is part of a consultation on the Red List implications of extensive changes to BirdLife’s taxonomy for non-passerines
Lynx Edicions and BirdLife International will soon publish 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 1 of the checklist (for non-passerines) will begin to be incorporated into the 2013 Red List update, with the remainder, and those for passerines (which will appear in volume 2 of the checklist), 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.
White-crested Hornbill Tropicranus albocristatus is being split into T. albocristatus and T. cassini, following the application of criteria set out by Tobias et al. (2010).
Prior to this taxonomic change, T. albocristatus (BirdLife species factsheet) was listed as Least Concern on the basis that it was not thought to approach the thresholds for Vulnerable under any of the IUCN criteria. This species was estimated to have an extremely large range, and hence did not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence of less than 20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appeared to be stable, and hence the species did not approach the thresholds for Vulnerable under the population trend criterion (at least a 30% decline over ten years or three generations). The population size has not been quantified, but it was not believed to approach the thresholds for Vulnerable under the population size criterion (fewer than 10,000 mature individuals with a continuing decline estimated to be at least 10% over ten years or three generations, or with a specified population structure).
T. albocristatus (as defined following the taxonomic change, and incorporating macrourus) occurs in West Africa, from southern Sierra Leone, east to Benin, where it inhabits primary forest as well as tall gallery and secondary forest and adjacent deciduous woodland (del Hoyo et al. 2001). It may warrant listing as Near Threatened under criteria A2cd+3cd+4cd, on the basis that it could be undergoing a moderately rapid population decline (approaching 30% over three generations [c.24 years]) owing to on-going deforestation and potential hunting pressure. It is not thought to be declining more rapidly than this because it shows some flexibility in its habitat requirements.
T. cassini occurs in Central-west Africa, from Nigeria, east to western Uganda and south to northern Angola, where it occupies a similar range of forest and woodland habitats (del Hoyo et al. 2001). It is likely to warrant listing as Least Concern, on the basis that it is not thought to approach the thresholds for Vulnerable under any of the IUCN criteria.
Comments on these suggested categories are invited and further information would be welcomed.
References:
del Hoyo, J., Elliott, A. and Sargatal, J. (2001) Handbook of the birds of the world, Vol 6: Mousebirds to Hornbills. Barcelona, Spain: Lynx Edicions.
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.
Related posts:
- Piping Hornbill (Bycanistes fistulator) is being split: list B. fistulator as Near Threatened?
- Archived 2011-2012 topics: Yellow-casqued Hornbill (Ceratogymna elata) and Brown-cheeked Hornbill (Bycanistes cylindricus): request for information
- Forest Woodhoopoe (Phoeniculus castaneiceps) is being split: list P. castaneiceps as Near Threatened?
- Dwarf Black Hornill (Tockus hartlaubi) is being split: list T. hartlaubi as Near Threatened?
T. albocristatus (and probably T. cassini) occurs in a broad range of habitats, including cocoa and coffee plantations with mature forest trees. Thus, the habitat available for this species is broader than the remaining extent of forest. I have not, however, observed it in woodland, north of the forest zone.
The range and estimation of change in distribution over time should include the loss of forest as well as the gain in plantations with mature trees. If this still exceeds 30% in 24 years then near-threatened is likely.