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.
Torrent Robin Monachella muelleriana is being split into M. muelleriana and M. coultasi, following the application of criteria set out by Tobias et al. (2010).
Prior to this taxonomic change, Monachella muelleriana (BirdLife species factsheet) was listed as Least Concern on the basis that it did not approach the thresholds for listing as Vulnerable under any criteria. The pre-split species was characterised as locally common and probably present on all suitable streams, but also as often scarce (Boles 2016). Potentially there are some seasonal movements or variation in detectability throughout the seasons. A density of 1 pair every 200 m of stream has been reported (Boles 2016).
M. muelleriana (as defined following the taxonomic change) is found throughout much of New Guinea along suitable streams typically in hills and mountainous areas between 300-2,100 m altitude, while M. coultasi inhabits fast-flowing, rocky, braided rivers in the east of New Britain, between at least 300-750 m (Dutson 2011).
M. coultasi has apparently only been recorded from a single river in east New Britain, with potentially only four suitable rivers present (G. Dutson in litt. 2016). While the extent of occurrence of the split species is calculated at 25,107 km2, the actual occupied range is a tiny percentage of this and arranged linearly. The entire length of suitable sections of rivers in the species’ apparent range is below 100km, which at the estimate of 1 pair per 200 m (which is likely to be at maximum occupancy, and was not made on New Britain) indicating that the population falls in the range 1,000-2,499 individuals, equivalent to 667-1,666 mature individuals, rounded here to 600-1,700 mature individuals.
Threats to the species are not well known, and it utilises sections of streams with open space around as occurs with small landslips (Dutson 2011). However the response of the species to the removal of streamside vegetation is not documented, nor is it clear why it appears so restricted on New Britain. Rivers in the area which the species occurs are used as significant access routes and there is evidence of clearing along their banks by small-holders for agriculture (Hansen et al. 2013). There does not appear to be any particular reason to infer that the population is declining, and on New Guinea Monachella muelleriana is often found on rivers in degraded habitat.
On a precautionary basis New Britain Flyrobin M. coultasi is suggested to be listed as Near Threatened, on the basis that it may well approach the thresholds for listing as Vulnerable under criterion D1, due to a likely very small population size.
Should the species actually be more widely distributed, therefore the length of suitable river habitat be considerably greater, then the species should be considered Least Concern.
Comments are invited on these proposed categories and further information would be welcomed.
Boles, W. (2016). Torrent Flyrobin (Monachella muelleriana). 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/59326 on 10 October 2016).
Dutson, G. 2011. Birds of Melanesia: Bismarcks, Solomons, Vanuatu and New Caledonia. Christopher Helm, London.
Hansen, M. C., P. V. Potapov, R. Moore, M. Hancher, S. A. Turubanova, A. Tyukavina, D. Thau, S. V. Stehman, S. J. Goetz, T. R. Loveland, A. Kommareddy, A. Egorov, L. Chini, C. O. Justice, and J. R. G. Townshend. 2013. High-Resolution Global Maps of 21st-Century Forest Cover Change. Science 342: 850–53. Data available on-line from: http://earthenginepartners.appspot.com/science-2013-global-forest. Accessed through Global Forest Watch on 10th October 2016. www.globalforestwatch.org
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.