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.
Ryukyu Robin Erithacus komadori is being moved into the genus Larvivora and split into Larvivora komadori and L. namiyei, following the application of criteria set out by Tobias et al. (2010).
Prior to this taxonomic change, Erithacus komadori (BirdLife species factsheet) was listed as Near Threatened as it was believed to approach the thresholds for Vulnerable under criteria B1ab(i,ii,iii,iv,v), on the basis that it had a moderately small and declining range. However it is likely that the species occurs at considerably more than 11-20 locations* suggesting that criterion B may not be appropriate. The pre-split species was characterised as common on Tokara Island and Amami and locally common on Okinawa but scarce on other islands with a total population estimated at 100,000 birds (Collar 2016), but is suggested to have declined since this estimate was made at least in parts of the range (Clement and Rose 2015). It inhabits undergrowth and ground-strata vegetation in evergreen forest (Clement and Rose 2015).
L. komadori is found from Tanegashima south to Tokunoshima in the northern Ryukyu Islands, while L. namiyei is restricted to the island of Okinawa. L. komadori is partly migratory, moving south to the southernmost islands in the chain and occasionally reaching Chinese Taiwan (Clement and Rose 2015).
For the new nominate L. komadori the extent of occurrence (EOO) is likely to be under 10,000km2, and for L. namiyei it is likely to be below 2,500km2. Both are now considered to consist of only a single subpopulation, although Clement and Rose (2015) indicate that L. namiyei may also be present on the Kerama Islands.
The populations of both L. komadori and L. namiyei are estimated to number 10,000-19,999 individuals based on an assessment of known records, descriptions of abundance and range size. This is consistent with recorded population density estimates for congeners or close relatives with a similar body size, and the fact that only a proportion of the estimated Extent of Occurrence is likely to be occupied. This estimate is equivalent to 6,667-13,333 mature individuals, rounded here to 6,000-15,000 mature individuals.
This estimate is lower than that previously given for the formerly recognised species, but previously this was considered to occur as a resident over an area of occupancy of 2,700km2, whereas the combined estimated area of suitable habitat on the islands the species is now considered to breed upon is actually just over 1,000km2.
It is proposed that Ryukyu Robin L. komadori is listed as Near Threatened, on the basis that it approaches the thresholds for listing as Vulnerable under criterion C2a(ii). If there was evidence that the species was severely affected by introduced predators then the number of locations* for the species could be considered close to 10, which may qualify the species for listing as Near Threatened or Vulnerable under criterion B1ab(ii,iii,v). There does not appear to be evidence for a significant population reduction within the past three generations.
L. namiyei shares a range with the Endangered Okinawa Rail Hypotaenidia okinawae, though does not share that species’ susceptibility to the introduced mongoose and road kill that has caused such a considerable decline in that species. However, logging, dam construction and associated road-building, agricultural development and golf course construction are inferred to be causing an ongoing population decline in the species. It is suggested that Okinawa Robin L. namiyei is listed as Near Threatened as it is thought to approach the thresholds for listing 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).
Clement, P. and Rose, C. 2015. Robins and Chats. Christopher Helm, London.
Collar, N. (2016). Ryukyu Robin (Luscinia komadori). 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/58466 on 5 October 2016).
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.
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.