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.
Japanese Robin Larvivora akahige is being split into L. akahige and L. tanensis, following the application of criteria set out by Tobias et al. (2010).
Prior to this taxonomic change, L. akahige (BirdLife species factsheet) was listed as Least Concern, on the basis that it was not believed to approach the thresholds for listing under any of the criteria. The pre-split species was characterised as common, locally common or even abundant in Japan (Clement and Rose 2015). L. a. tanensis has been described as rare (Clement and Rose 2015), and as common (Collar 2016) and is considered resident (Clement and Rose 2015).
L. akahige (as defined following the taxonomic change) breeds on Sakhalin, the south Kuril Islands and Japan, including islands south of Kyushu and occurs in the non-breeding season in south east China and Chinese Taiwan.
L. tanensis Izu Robin is restricted to the Izu Islands, south of Honshu in Japan. The extent of occurrence (a minimum convex polygon incorporating all known parts of the range) is approximately 5000 km2, while a maximum area of occurrence (the total area of the islands upon which it could occur) is approximately 320 km2. The species shares this range with Izu Thrush Turdus celaenops (BirdLife Species Factsheet) and Izu Leaf-warbler Phylloscopus ijimae (BirdLife Species Factsheet). For these species an ongoing population decline is suspected; for Izu Thrush the impact of introduced predators is thought to have caused an observed rapid decline and for Izu Leaf-warbler habitat loss and fragmentation are considered to be causing a moderate decline. Siberian Weasel was introduced to Miyake-jima in the 1970s and domestic cats are also widely present, additionally enhanced populations of Large-billed Crow as a result of the availability of food via poor human rubbish disposal. Large areas of natural forest have been replaced by Cryptomeria for timber, although L. tanensis does occur in this habitat (Clement and Rose 2015). Road-building and the creation of tourist infrastructure have also been noted to have reduced the extent of natural habitat.
In addition the impact of volcanic eruptions is a potential threat to populations in that these events can degrade large areas of habitat. The eruption in 2000 of Mt. Oyama is estimated to have degraded 60% of forest on Miyake-jima, however populations of birds were observed to recover relatively quickly from this event.
Recent eBird reports demonstrate that the species has been seen frequently on Miyake-jima and Hachijo-jima, but the situation on Oshima is unclear.
On the evidence, it is considered that Izu Robin is likely to be suffering a minor ongoing decline. There has been no quantification of the current population trend, but the population does not appear to have been affected by introduced predators to the same extent as Izu Thrush.
The population is estimated to number 2,500-9,999 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 1,667-6,666 mature individuals, rounded here to 1,500-7,000 mature individuals.
It is suggested that Izu Robin L. tanensis is listed as Vulnerable under criterion C2a(i) on the basis that it has a small population arranged in several subpopulations (islands), none of which exceeds 1,000 mature individuals, and is subject to an inferred ongoing decline.
Should the total population of the species be considered larger than 10,000 mature individuals, or a subpopulation larger than 1,000 mature individuals, the species might be considered more appropriately listed as Near Threatened under the same criterion.
To be considered for listing under the geographic range criterion, B, the population would need to be considered severely fragmented or for the species to occur at fewer than 11 locations*. The evidence from the significant eruption of Miyake-jima in 2000 and continued persistence of the species subsequently indicates that even in terms of such a destructive event there must be multiple locations present on this island and that this is likely true for the other larger islands. Consequently the number of locations at present is judged to be in excess of 11.
Information on the population size and trends are sought, and the genetic structure of the populations on the different islands within the range of the species is also of interest
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). Japanese Robin (Luscinia akahige). 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/58465 on 3 October 2016).
eBird. 2016. eBird: An online database of bird distribution and abundance [web application]. eBird, Ithaca, New York. Available: http://www.ebird.org. (Accessed: October 3, 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.