Seychelles Warbler (Acrocephalus sechellensis – BirdLife species factsheet) is currently classified as Vulnerable under Criterion D2, since it was confined to just four tiny islands with a very small range and was thought to be at risk from introduced predators.
A. sechellensis was present on several islands in the Seychelles until human disturbance in the 20th century reduced the species to a single population on the tiny (0.3 km2) island of Cousin between 1920 and 1988. In 1968 the species numbered fewer than 30 individuals. Conservation efforts were directed towards the species, which was translocated to the islands of Aride, Cousine and Denis between 1998 and 2004 and recovered to an estimated 2,500 individuals by 2007 (Bristol 2005; Richardson et al. 2006; G. Rocamora in litt. 2007). A species action plan produced in 2001 recommended that the range of the species be increased to five islands through translocations to secure the future of the species (Richardson 2001).
In December 2011, 59 adult Seychelles Warblers were captured on Cousin Island and translocated to Frégate Island (Wright et al. 2014). At the time of the translocation, Frégate Island possessed 0.37 km2 of habitat suitable for A. sechellensis and this was predicted to increase to 0.42 km2 by 2016 as a result of regeneration work. By June 2013, the A. sechellensis population on Frégate had increased to 80 individuals, which included 38 of the original translocated birds and 42 birds which had hatched on Frégate. Six birds were the offspring of birds that had themselves hatched on Frégate, indicating that a second generation had hatched on the island since the translocation. The source population on Cousin recovered to carrying capacity by October 2012.
The total population was estimated in 2014 at approximately 2,800 adults (N. Shah in litt): 320 on Cousin (Brouwer et al. 2006), 2010 on Cousine (Van de Crommenacker and Richardson 2007), 1,850 on Aride (Orchard 2004), 300 on Denis (J. van der Woude, unpub. data) and 80 on Frégate (Teunissen 2013). It has been predicted that as the newer populations reach carrying capacity, the total population will exceed 7,000 birds (Wright et al. 2014).
Although the range of A. sechellensis remains very small, the species now has five populations on five islands and its population has further increased to an estimated 2,800 individuals. It may therefore be considered that the risk of introductions of predators is no longer likely to drive the species to Critically Endangered or Extinct in a very short time. As a result, it may no longer be justified to list the species as Vulnerable under Criterion D2 and it may be more appropriate to downlist the species to Near Threatened.
Additional information and comments on this proposal are welcomed.
Bristol, R. 2005. Conservation introductions of Seychelles Fody and Warbler to Denis Island, Seychelles. Re-introduction News 24: 35-36.
Brouwer, L., Richardson, D.S., Eikenaar, C. & Komdeur, J. 2006. The role of group size and environmental factors on survival in a cooperatively breeding tropical passerine. Journal of Animal Ecology 75: 1321-1329.
Orchard, D. 2004. Aride Seychelles Warbler Census. In: Betts, M. (ed.) Annual Report 2003. Aride Island Nature Reserve, Seychelles. Royal Society of Wildlife Trusts, Newark.
Richardson, D.S. 2001. Species Conservation Assessment and Action Plan: Seychelles warbler (Timerl Dezil). Joint report of Nature Seychelles, University of East Anglia, Norwich.
Richardson, D.S., Bristol, R. & Shah, N.J. 2006. Translocation of the Seychelles warbler Acrocephalus sechellensis to establish a new population on Denis Island, Seychelles. Conservation Evidence 3: 54-57.
Teunissen, N. 2013. A newly translocated population of the Seychelles warbler: is there evidence for interspecific competition with Seychelles white-eyes? MSc thesis. University of Groningen.
Van de Crommenacker, J. & Richardson, D.S. 2007. Monitoring and Studying the Seychelles warbler: fieldwork on Cousine Island. University of Groningen Report, Groningen.
Wright, D.J., Shah, N.J. & Richardson, D.S. 2014. Translocation of the Seychelles warbler Acrocephalus sechellensis to establish a new population on Frégate Island, Seychelles. Conservation Evidence 11: 20-24.