White-throated Eared-nightjar (Eurostopodus mystacalis) is being split: list E. exul as Critically Endangered (Possibly Extinct) and E. nigripennis as Vulnerable?

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-throated Eared-nightjar Eurostopodus mystacalis is being split into E. mystacalis, E. exul and E. nigripennis, following the application of criteria set out by Tobias et al. (2010).

Prior to this taxonomic change, E. mystacalis (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). Despite the fact that the population trend appeared to be decreasing, the decline was not believed to be sufficiently rapid to 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).

E. exul is known only from north-western New Caledonia, where a single specimen was collected from ‘coastal flats’ in 1939 (Mayr 1941 in del Hoyo et al. 1999, Holyoak 2001). The species is thought to be extinct (Dutson 2011), but is very poorly known, and is perhaps best classed as Critically Endangered (Possibly Extinct), as suggested by Szabo et al. (2012). This listing is suggested under criterion D1, on the basis that, if it is still extant, there are likely to be fewer than 50 mature individuals remaining, given that it is known from just one specimen.

E. nigripennis is endemic to Bougainville and the Solomon Islands, where it occurs in coastal habitats, such as beaches and offshore islets (del Hoyo et al. 1999, Holyoak 2001). It is suggested that it qualifies as Vulnerable under criterion C2a(i), on the basis that it is estimated to number fewer than 2,500 mature individuals, given its apparent rarity (Holyoak 2001), with all subpopulations thought to number fewer than 1,000 mature individuals (but all or most subpopulations deemed likely to exceed 250 mature individuals), and an on-going decline is inferred based on a decreasing frequency of records (Dutson 2011) and the likely threat of disturbance to beaches.

E. mystacalis (as defined following the taxonomic change) is widely distributed in eastern New Guinea and eastern Australia, where it uses a variety of habitats, including modified areas (del Hoyo et al. 1999, Holyoak 2001). It is likely to warrant classification as Least Concern on the basis that it is not thought to approach the thresholds or Vulnerable under any of the IUCN criteria.

Comments are invited on these suggested categories and further information would be welcomed.

References:

del Hoyo, J., Elliott, A. and Sargatal, J. (1999) Handbook of the birds of the world, Vol 5: Barn- owls to Hummingbirds. Barcelona, Spain: Lynx Edicions.

Dutson, G. (2011) Birds of Melanesia: Bismarcks, Solomons, Vanuatu and New Caledonia. London: Christopher Helm (Helm Field Guides).

Holyoak, D. T. (2001) Nightjars and their allies: the Caprimulgiformes. Oxford: Oxford University Press (Bird Families of the World).

Szabo, J. K., Khwaja, N., Garnett, S. T., Butchart, S. H. M. (2012) Global Patterns and Drivers of Avian Extinctions at the Species and Subspecies Level. PLoS ONE 7(10): e47080. doi:10.1371/journal.pone.0047080

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.

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