This discussion was first published as part of the 2013 Red List update, but remains open for comment to enable reassessment in 2015.
Long-billed Tailorbird Artisornis moreaui occurs at low density in two widely separated forests, the East Usambaras in Tanzania (nominate subspecies) and the Njesi Plateau in northern Mozambique (subspecies sousae), where it was rediscovered (Ryan and Spottiswoode 2003), having not been visited since 1945 (Benson 1946). It is currently listed as Critically Endangered under criterion C2a(ii) because its low population density and the small area of suitable habitat available indicate that its total population is extremely small (50-249 mature individuals), it is likely to be undergoing a continuing decline given that much of its habitat is being altered rapidly, and over 90% of its global population has been suspected to be confined to one subpopulation.
In the East Usambaras it is more common than previously suggested (Cordeiro 2000), but still somewhat local and infrequent. Records from Mt Nilo were followed by the discovery of territories around Zirai in May 2009, and later surveys located a total of ten territories in Nilo Nature Reserve, in the areas of Nkombola, Kweng’wiza, Kilangangua and Kiziga and northward to Lutindi (Kyonjola and Njilima 2010). The species occurs over ten broad localities near Amani (Cordeiro 1998, Baker and Baker 2001); Amani Nature Reserve was conservatively estimated to hold 150-200 individuals in 2000 (Cordeiro 2000), and surveys in 2008-2009 found around 80 territories at Amani and in the surrounding area. However, recent survey work has since identified further territories, including 20 in the Nilo Nature Reserve (N. Cordeiro in litt. 2011). The total population of Long-billed Tailorbird was estimated to be 371 individuals in East Usambara; larger than the previous estimates for the global population of the species (N. Cordeiro in litt. 2011). The largest subpopulation is at Mt Nilo which covers 43.6 km2 and may hold up to 75% of the total East Usambaras population (N. Cordeiro in litt. 2011). Nevertheless, only c.110 km2 of suitable habitat remains in the East Usambaras. Given that it is uncommon, elusive and exists at low densities, it may yet be found in other forests of the Eastern Arc (Baker and Baker 2001) now that the microhabitats and vocalisations are known (Cordeiro 2000, McEntree et al. 2005).
If this evidence is confirmed, and the global population of this species is greater than 250 mature individuals, it would no longer qualify as Critically Endangered under criterion C of the IUCN Red List and could warrant downlisting to a lower category of threat. If there is sufficient evidence to suggest that the population of this species is <2,500 mature individuals, it is in continuing decline and ≥95% mature individuals are in one subpopulation, it would warrant downlisting to Endangered under criterion C2a(ii). If evidence suggests that the global population is continuing to decline owing to habitat disturbance and alteration, its Extent of Occurrence (EOO) is <5,000 km2 and it is found at ≤5 locations, it could also qualify as Endangered under criterion B1ab(i,ii,iii,iv,v).
Information is requested on the distribution, population size and trends of this species. Comments on the proposed downlisting are also welcome.
Baker, N. E. and Baker, L. M. (2001) Tanzania. In: Fishpool, L.D.C.; Evans, M.I. (ed.), Important Bird Areas in Africa and associated islands: Priority sites for conservation, pp. 897-945. Pisces Publications and BirdLife International (BirdLife Conservation Series No.11): Newbury and Cambridge, UK.
Benson, C. W. (1946) A collection from near Unangu, Portuguese East Africa. Ibis 88: 240-241.
Cordeiro, N. J. (1998) A preliminary survey of the montane avifauna of Mt Nilo, East Usambaras, Tanzania. Scopus 20: 1-18.
Cordeiro, N. J. (2000) Report on a preliminary census of the Long-billed Tailorbird Orthotomus moreaui in the east Usambara Mountains.
McEntee, J., Cordeiro, N. J., Joho, M. P. and Moyer, D. C. (2005) Foraging observations of the threatened Long-billed Tailorbird Artisornis moreaui in Tanzania. Scopus 25: 51-54.
Ryan, P. G. and Spottiswoode, C. (2003) The conservation status of Long-billed Tailorbird Orthotomus moreaui and other birds on Serra Jeci, northern Mozambique. Ostrich 74: 141-145.