Archived 2014 discussion: Dwarf Black Hornbill (Tockus hartlaubi) is being split: list T. hartlaubi as Near Threatened?

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 2014 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.

Dwarf Black Hornbill Tockus hartlaubi is being split into T. hartlaubi and T. granti following the application of criteria set out by Tobias et al. (2010).

Prior to this taxonomic change, T. hartlaubi (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. hartlaubi is found in West Africa, from southern Sierra Leone and southern Guinea, east to southern Cameroon and south-western Central African Republic, and south to Gabon and northern Congo, where it inhabits tall primary evergreen and gallery forest, only rarely occurring in secondary forest (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.29 years]) owing to on-going deforestation and habitat degradation, and potential levels of hunting.

T. granti occurs in Central Africa, from east-central Congo and Democratic Republic of Congo, east to South Sudan and western Uganda, and south to north-western Angola (Cabinda), where it occupies similar habitats to those inhabited by the nominate part of the split (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:

  1. Archived 2011-2012 topics: Knobbed Hornbill (Aceros cassidix) and Sulawesi Hornbill (Penelopides exarhatus): uplist to Near Threatened?
  2. Archived 2011-2012 topics: Yellow-casqued Hornbill (Ceratogymna elata) and Brown-cheeked Hornbill (Bycanistes cylindricus): request for information
  3. Archived 2012-2013 topics: Dwarf Tinamou (Taoniscus nanus): downlist to Near Threatened or Least Concern?
  4. Archived 2012-2013 topics: Dwarf Honeyguide (Indicator pumilio): downlist to Least Concern?
  5. Archived 2012-2013 topics: Black Bustard (Eupodotis afra): eligible for uplisting?
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5 Responses to Archived 2014 discussion: Dwarf Black Hornbill (Tockus hartlaubi) is being split: list T. hartlaubi as Near Threatened?

  1. Hugo Rainey says:

    This split seems reasonable based on plumage and other differences.

    The range of this species includes areas under imminent threat (Upper and Lower Guinea), but also areas which are quite secure. Is the rate of forest loss, and thus the inferred rate of population decline, really as great as for Tropicranus albocristatus which occurs only from Upper Guinea east to Benin? Its habitat preference is narrower than the latter species, but the area of intact forest is still high. Also, is this species really threatened by hunting? A small mid-upper storey, secretive bird is not often a common hunting target as it only weighs a few hundred grammes.

    How has the generation length been estimated – 29 years? I think it unlikely that this species would have a generation length longer than the larger Tropicranus albocristatus which is probably its closest relative (based on behaviour).

  2. Jeremy Lindsell says:

    This was certainly always the rarest of the hornbills I encountered in Sierra Leone but it was not confined to intact forest in and around Gola. Having a range that extends into central Africa suggests to me that it is unlikely to qualify as NT.

  3. Andy Symes says:

    The following comments were received from Françoise Dowsett-Lemaire on 20 August 2013:

    Tockus hartlaubi. Nominate race has a huge range extending from West Africa to Central Africa, with very large forest blocks in Gabon and N. Congo-Brazzaville. In West Africa and elsewhere tolerates logging and is in fact more common in open-canopy, logged forest than in mature, closed-canopy forest. In Ghana, its range is continuous within the forest zone of the south-west. Definitely a “least concern” species or form.

  4. Joe Taylor says:

    Preliminary proposals

    Based on available information and comments posted above, our preliminary proposals for the 2014 Red List would be to treat:

    T. hartlaubi as Least Concern

    T. granti as Least Concern

    There is now a period for further comments until the final deadline of 31 March, after which recommended categorisations will be put forward to IUCN.

    The final Red List categories will be published on the BirdLife and IUCN websites in mid-2014, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  5. Andy Symes says:

    Recommended categorisations to be put forward to IUCN

    Following further review, there have been no changes to our preliminary proposals for the 2014 Red List status of these species.

    The final categorisations will be published later in 2014, following further checking of information relevant to the assessments by BirdLife and IUCN.

Comments are closed.