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.
Blue-crested Flycatcher Myiagra azureocapilla is being split into M. azureocapilla and M. castaneigularis following the application of criteria set out by Tobias et al. (2010).
Prior to this taxonomic change, M. azureocapilla (BirdLife species factsheet) was listed as Least Concern, on the basis that it was not believed to approach the thresholds for Vulnerable under any of the criteria. The pre-split species was characterised as quite regularly observed, though not as common as Vanikoro Flycatcher M. vanikorensis. It occurs in mature forest only (Gregory 2016).
M. azureocapilla (as defined following the taxonomic change) is restricted to the island of Taveuni in N Fiji, while M. castaneigularis is found on Viti Levu and Vanua Levu, Fiji. While the latter has a restricted range, it is not believed to approach the thresholds for Vulnerable under any of the criteria, though the population size has not been quantified. It is suggested that M. castaneigularis is listed as Least Concern.
The newly-split M. azureocapilla has an extent of occurrence calculated as only 540 km2, and all individuals are considered to be in a single population. A large proportion of the species’ range lies within the Taveuni Highlands IBA, within which it is described as common (BirdLife International 2016). A significant proportion of this remains designated as Reserved Forest, providing only limited protection and there is a level of ongoing conversion for small-holder farming (BirdLife International 2016). As with the similarly distributed Silktail Lamprolia victoriae it is suspected the population trend is decreasing. Additionally the small population and restricted range leave the species at risk of becoming threatened in a short time frame due to stochastic events such as cyclones or the introduction of non-native predators: notably no mongooses have established on Taveuni as yet.
The population is 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, 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.
It is suggested that the species should be listed as Near Threatened as it is considered to approach the thresholds for Vulnerable under criteria B1ab(iii,v)+2ab(iii,v); C2a(ii).
If there is evidence that the number of locations* occupied by the species is fewer than 11 then the species would qualify as Vulnerable under criterion B1ab(iii,v)+2ab(iii,v).
Equally, should there be evidence that the population size was below 10,000 mature individuals then it would qualify 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).
BirdLife International (2016) Important Bird and Biodiversity Area factsheet: Taveuni Highlands. Downloaded from http://www.birdlife.org on 30/09/2016
Gregory, P. (2016). Azure-crested Flycatcher (Myiagra azureocapilla). 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/59261 on 30 September 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.