|Scientific Name:||Acrocephalus luscinius|
|Species Authority:||(Quoy & Gaimard, 1830)|
|Taxonomic Notes:||Gender agreement of species name follows David and Gosselin (2002a).|
|Red List Category & Criteria:||Critically Endangered A3bce+4bce ver 3.1|
|Reviewer/s:||Butchart, S. & Symes, A.|
|Contributor/s:||Amidon, F., Camp, R., Dutson, G., Freifeld, H., Mosher, S., Radley, P. & Saunders, A.|
This species qualifies as Critically Endangered because the very rapid rate of decline in its very small global population observed over the past three generations is expected to increase owing to habitat loss and degradation combined with the impact of introduced predators including brown tree snake Boiga irregularis on Saipan. This snake is a likely factor in the reed-warbler's extirpation from Guam.
|Range Description:||This species is historically known from Guam (to USA), Saipan, Alamagan, Aguijan and Pagan in the Northern Mariana Islands (to USA), and from a specimen thought to have come from Yap, Federated States of Micronesia. The subspecies yamashinae of Pagan was extinct by the late 1970s, and astrolabii, whose type specimen is thought to be from Yap, is also extinct (Reichel et al. 1992, Kennerley and Pearson 2010). The species has also been extirpated from Guam. A tiny population was reported to occur on uninhabited Aguijan (1-6 birds) but has not been observed on the island since the mid-1990s despite extensive surveys in 2000, 2001, 2008, and 2009 (USFWS 1998, Esselstyn et al. 2003, Camp et al. 2009b), and so is unlikely to number more a few individuals, if any (Marshall et al. 2008). A population exists on Alamagan, numbering 1,125 (95% CI = 504 - 1,539) individuals in 2000 and 946 (95% CI = 428-1,762) individuals in 2010 (Marshall et al. 2011). The majority of the population occurs on Saipan. Abundance (density * the area of Saipan, 115.39 km2) with 95% Confidence Intervals 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 the 2007 survey (Camp et al. 2009a). This represents a 59% decline in the species since 1982. 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 rapid human expansion on Saipan in the 1990s has been slowing since c. 1998, but the U.S. military is expanding its presence and operations which could lead to further habitat conversion and degradation, if this expansion occurs on Saipan or Alamagan. Furthermore, persistent reports from the island of Saipan suggest that Boiga irregularis may be in the process of becoming established there (Rodd and Savidge 2007). This is cause for concern given the catastrophic declines it caused on Guam's birds.|
Native:Northern Mariana Islands
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Three island populations currently exist: Aguijan (1-2 indidivuals [Marshall et al. 2008]), Alamagan (946 individuals [Marshall et al. 2011]) and Saipan (2,742 individuals [Camp et al. 2009a]). This equates to a global population of c.3,700 individuals. However, given the rapid decline occurring on Saipan and that a proportion of the population will be immature birds this is cautiously interpreted as 2,000-2,499 mature individuals.|
|Habitat and Ecology:||On Saipan, it occurs in thicket-meadow mosaics, forest edge, reed-marshes and forest openings (Craig 1996). A recent study on Saipan found nests in upland introduced Leucaena leucocephala forest, a native mangrove wetland and a native reed wetland (Mosher and Fancy 2002). On Alamagan, it inhabits open forest with brushy understorey and wooded ravine forest adjacent to open grasslands. On Aguijan, it inhabits formerly disturbed areas vegetated by groves of trees and thickets. On Guam and Pagan, it was almost exclusively found in freshwater wetland and wetland edge vegetation (Engbring et al. 1982, Reichel et al. 1992, USFWS 1998).|
On Guam, several factors in combination are likely to have caused the species's extirpation, including wetland destruction, predation by the introduced brown tree snake Boiga irregularis, pesticide-use and major fires. On Saipan, available habitat has been reduced for agriculture, home-building and tourist-related facilities. Persistent reports from the island of Saipan suggest that the brown tree snake may be in the process of becoming established there (Rodd and Savidge 2007) and unless it can be controlled, the reed-warbler population is likely to be extirpated rapidly once snake numbers have reached the point where they impact bird populations. Ivy Gourd Coccinia grandis became established in the mid-1990s and has effectively invaded >90% of forest stands on Saipan (S. Mosher in litt. 2012). This species covers forest canopies, effectively smothering the canopy to the point of killing trees to causing the collapse of the canopy, therefore reducing the canopy height that is important for nesting reed-warblers (S. Mosher in litt. 2012). The habitat on Alamagan is heavily degraded from grazing by feral ungulates (F. Amidon in litt. 2012, N. Johnson in litt. 2012). Introduced predators, including feral cats Felis catus and rats Rattus spp., and possibly monitor lizard Varanus indicus, may be a large factor in the reported high proportion of nest failures (USFWS 1998, Mosher 2006).
Conservation Actions Underway
A recovery plan exists (U.S. Fish and Wildlife Service 1998) but there has been little or no active management for the species to date and the milestones in the plan are now out of date. However, provisions to protect habitat and mitigate loss have generally been included in major land development projects. In 1989, a goat removal programme was begun on Aguijan but, by 1995, goat populations had begun to rebound with reduced hunting pressure. Trap lines for snakes are maintained at ports, night searches are conducted and a sniffer dog programme has recently been established. Publicity campaigns were conducted to raise the general awareness of island residents, including port workers, about the dangers of snake colonisation (USFWS 1998). Repeat surveys have been conducted on Saipan in 1982, 1997 and 2007; on Aguijan in 2000, 2001, 2008, and 2009 (USFWS 1998, Esselstyn et al. 2003, Camp et al. 2009b); and on Alamagan in 2000 and 2010 (Marshall et al. 2011).
Conservation Actions Proposed
Monitor the populations on all three islands (USFWS 1998). Protect Saipan, and also Alamagan, from snake colonisation. Control feral ungulates and predators, including B. irregularis (USFWS 1998). Continue control of Coccinia grandis with particular emphasis on reed-warbler nesting sites. Identify and protect essential habitat and conduct basic research, e.g. on population dynamics and validity of subspecies, to assist in appropriate recovery efforts (USFWS 1998). Establish additional populations on other islands (USFWS 1998). Clarify the status of B. irregularis on Saipan and mitigate the potential effects should its number increase.
|Citation:||BirdLife International 2012. Acrocephalus luscinius. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 19 May 2013.|
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