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.
Nightingale Reed Warbler Acrocephalus luscinius is being split into Guam Reed-warbler A. luscinius, Pagan Reed-warbler A. yamashinae, Aguijan Reed-warbler A. nijoi, Saipan Reed-warbler A. hiwae and Mangareva Reed-warbler A. astrolabii, following the application of criteria set out by Tobias et al. (2010).
Prior to this taxonomic change, A. luscinius (BirdLife species factsheet) was listed as Critically Endangered under criterion A3bce + 4bce, on the basis that a rapid observed population reduction over the previous three generations had increased to a rate in excess of 80% for a three generation period including both the past and the future, and projected to exceed 80% into the future. The species additionally qualified as Endangered under criteria A2bce + 3bce + 4bce; B1ab(i, ii, iii, iv, v), and Vulnerable under all the above criteria plus C2a(i) and D2. The population has been cautiously interpreted as 2,000-2,499 mature individuals, from population estimates in 2009 of 2,742 individuals on Saipan and 946 individuals on Alamagan.
The pre-split species had suffered dramatic declines, extinctions and near extinctions on different islands included within the formerly single taxon. On Guam and Pagan the species was primarily restricted to freshwater wetland habitats, while on the other islands it occurs in thicket-meadow mosaics, forest edge, Phragmities reed-marshes and openings and damaged areas of forest (Craig 1996, Dyrcz and Sharpe 2016).
A. hiwae is found only on the islands of Alamagan and Saipan, while the newly defined A. luscinius is the species previously restricted to Guam. A. nijoi was restricted to Aguijan and A. yamashinae was found only on Pagan Island. A. astrolabii is known only from two specimens collected in 1838 or 1839, but it is not possible to ascertain precisely where they originated (Kennerley and Pearson 2010). It has been speculated that Yap might have been the home of the species, but it has not been seen anywhere subsequent to the original collection (Holyoak and Thibault 1978).
Following recognition as a species Aguijan Reed-warbler A. nijoi is of the utmost conservation concern, but is likely to already be extinct. Engbring et al. (1986) estimated 15 birds on the island in 1982, two singing males were observed in 1992 (Craig and Chandran 1992, cited in Marshall et al. 2009), one in 1993 (Lusk 1993, in Marshall et al. 2009) and a single male was observed in 1995 by Annie Marshall (USFWS 1998). Additional surveys in 2000 and 2002, and a focus study in 2008 failed to find any evidence of the species (Marshall et al. 2009). There is some indication that one or more of the recent observations may pertain to individuals of A. hiwae from Saipan (Marshall et al. 2009). However, there remains the vague possibility that the species is still extant, and for this reason A. nijoi is suggested to be listed as Critically Endangered (Possibly Extinct).
The population of Saipan Reed-warbler A. hiwae is thought to continue to decline very rapidly. Abundance on Saipan declined from 6,658 birds (5,331-8,054) in 1982 down to 4,639 (3,669-5,689) birds in 1997, and has continued to decline to 2,742 birds (1,686-3,956) in 2007 (Camp et al. 2009). Over three generations this equates to an overall population decline of 47%, but this rate of decline has been increasing such that the rate recorded between 1997 and 2007 corresponds to a three generation decline of 60%. The reasons for the decline are not fully understood, but are likely to due to the impact of introduced species including feral rats, cats and monitor lizards, and also the Ivy Gourd Coccinia grandis altering available habitat. As yet the anticipated full establishment of Boiga irregularis on Saipan has not happened due to a high level of awareness and ongoing significant biosecurity and control efforts, but it is still considered a very serious likelihood. It is proposed that the species retains the status of Critically Endangered, under criterion A3bce + A4bce, but if there is evidence that the population declines have not been as severe as thought within the current period and the risk of future very high rates of decline are lower, then the species may become eligible for downlisting. The fate of the other species previously included with this last one standing must be recognised as a warning not to underestimate to potential danger to this species.
Mangareva Reed-warbler A. astrolabii is considered to be Extinct, its exceptionally stout feet losing their grip on existence sometime prior to the late-20th century. It was not recorded since the type series collection in 1838 or 1839 (Holyoak and Thibault 1978, Kennerley and Pearson 2010). Given that the precise home of this remarkable Acro has never been determined, the causes of this extinction are unknown.
Pagan Reed-warbler A. yamashinae is also Extinct. On Pagan virtually all vegetative ground cover was effectively removed at certain periods during the 20th century through a variety of agents including human development, introduced feral ungulates and finally a volcanic eruption in 1981 (Reichel et al. 1992). However there had not been any records for some time prior to this, with reports of reed-warblers being present by D. Aldan and J. Sablan into at least the 1960s (Reichel et al. 1992) appearing to be the last observations. Unsuccessful searches took place in the late 1970s (Tenorio and Associates 1979), between 1983 and 1989 (Reichel et al. 1992), in 1999 and 2000 (Division of Fish and Wildlife 2000) and in June 2010 (Marshall and Amidon 2010). The volcanic eruptions in 1981 appear to mark a full stop to the possibility of the species persisting, as all herbaceous and virtually all woody vegetation was destroyed in the last known site, around the upper lake (Reichel et al. 1992).
Guam Reed-warbler A. luscinius is also Extinct. The last confirmed sighting of this species was made in 1969, having been said to still be ‘fairly common’ in parts of the Agana Swamp in 1967 or 1968 before rapidly disappearing from this, the species’ last site (Reichel et al. 1992). As with A. yamashinae the species was primarily restricted to wetland habitats, which suffered considerable disturbance (Reichel et al. 1992). On Guam it is likely that the introduced Brown Tree Snake Boiga irregularis delivered the final blow to the species following significant habitat loss from drainage and fires, potential impacts from pesticides and impacts of a variety of additional introduced species (Reichel et al. 1992, Kennerley and Pearson 2010).
Comments are invited on these proposed categories and further information would be welcomed.
Craig, R. J. 1996. Seasonal population surveys and natural history of a Micronesian bird community. Wilson Bulletin 108: 246-267.
Division of Fish and Wildlife (DFW). 2000. Summary of wildlife surveys Pagan Island. Unpublished report by CNMI Division of Fish and Wildlife, Wildlife and Enforcement Sections and Northern Mayor’s Office, Saipan, CNMI. 68 pp.
Dyrcz, A. & Sharpe, C.J. 2016. Nightingale Reed-warbler (Acrocephalus luscinius). 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/58810 on 8 October 2016).
Holyoak, D.T. & Thibault, J.C. 1978. Undescribed Acrocephalus warblers from Pacific Ocean Islands. Bull. Brit. Orn. Club 98(4): 122–127.
Marshall, A.P. and Amidon. F.A. 2010. Status of the land and wetland avifauna of Pagan, Mariana Islands. Report to U.S. Fish and Wildlife Service, Pacific Islands Fish and Wildlife Office, 300, Ala Moana Boulevard, Honolulu, Hawaii. 30pp.
Reichel, J. D.; Wiles, G. J.; Glass, P. O. 1992. Island extinctions: the case of the endangered Nightingale Reed-warbler. Wilson Bulletin 104: 44-54.
Tenorio, J. C. and Associates. 1979. Ornithological survey of wetlands in Guam, Saipan, Tinian, and Pagan. U.S. Army Corps of Engineers, Pacific Ocean Div., Attn: CEPODCO, Building 230, Ft. Shafter, Hawaii 96858-5440.
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.
U.S. Fish and Wildlife Service (USFWS). 1998. Recovery plan for the nightingale reed-warbler, Acrocephalus luscinia. Portland, Oregon. 62pp.
Marshall, A.P., Amidon, F.A., Radley, P., Martin, G. and Camp. R. 2009. Nightingale Reed-warbler on Aguiguan. Section 2.4.4. Terrestrial Resource Surveys of Tinian and Aguiguan, Mariana Islands, 2008. Final Report. U.S. Fish and Wildlife Service, Pacific Islands Fish and Wildlife Office, Honolulu, HI.