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.
Chestnut-bellied Monarch Monarcha castaneiventris is being lumped with M. erythrostictus, and split into M. castaneiventris, M. ugiensis and M. megarhynchus, following the application of criteria set out by Tobias et al. (2010).
Prior to this taxonomic change, M. castaneiventris (BirdLife species factsheet) was listed as Least Concern, as was M. erythrostictus (BirdLife species factsheet), as neither were considered to approach the thresholds for listing as Vulnerable under any of the criteria. Both had been described as common, although M. castaneiventris was considered likely to be undergoing a population reduction due to habitat loss in the Solomon Islands.
M. castaneiventris (as defined following the taxonomic change, and incorporating M. c. erythrostictus, and M. c. obscurior) is found on Bougainville, Choiseul, Santa Isabel, Guadalcanal, Savo, Florida, Malaita and Russell Islands in the Solomons, while M. megarhynchus is restricted to the island of Makira (San Cristobal), and M. ugiensis is found on Ugi Island, and the Three Sisters Islands, Santa Ana and Santa Catalina, all off Makira in the South east Solomon Islands.
M. ugiensis has the smallest (if curious) range of the split species, with an Extent of Occurrence (EOO) of 2100km2, spread across a series of islands that total approximately 85km2, which can be taken as a maximum area of occupancy (AOO). However the population of the species on these islands is considered stable, given its apparent tolerance of disturbed habitats. The population is estimated at 1,000-2,499 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 is based on the maximum AOO. This estimate is equivalent to 667-1,666 mature individuals, rounded here to 600-1,700 mature individuals.
Given the small population size, but in the absence of evidence indicating a population decline, Ugi Monarch M. ugiensis is suggested to be listed as Near Threatened, on the basis that the number of mature individuals is thought to approach the threshold for listing as Vulnerable under Criterion D.
Were there to be evidence that the population was declining, the spread of the distribution is sufficient to consider that the population is severely fragmented, and the species may warrant listing as Endangered under criterion B1ab(iii, v) + B2ab(iii, v).
M. castaneiventris is suggested to be listed as Least Concern, on the basis that, as now constituted, it still does not approach the thresholds for listing as Vulnerable under any criteria.
M. megarhynchus has a newly calculated EOO of 4300km2, and the island of Makira (San Cristobal) continues to see ongoing logging and forest conversion, albeit at relatively slow rates. The species has been observed to be most abundant at intermediate levels of disturbance (Davies et al. 2015) and noted to be common to fairly common across a range of elevation bands. The population is estimated at 20,000-49,999 individuals based on an assessment of known records, descriptions of abundance and range size. M. megarhynchus is suggested to be listed as Least Concern, on the basis that, although there may be a slow population decline occurring, it is not believed to approach the thresholds for listing the species as Vulnerable under criterion A, and while the species has a restricted range it occurs at far more than 10 locations*.
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).
Davies, T.E., Clarke, R.H., Ewen, J.G., Fazey, I.R.A., Pettorelli, N and Cresswell, W. 2015. The effects of land-use change on the endemic avifauna of Makira, Solomon Islands: endemics avoid monoculture. Emu 115: 199-213.
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.