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Rota Bridled White-eye Zosterops rotensis
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Justification
This species qualifies as Critically Endangered because it is present on only one island and has an extremely small range which is declining owing to habitat loss and degradation. Its small population has declined very rapidly as a result of this habitat loss in combination with other factors. It may decline even more rapidly in the near future if brown tree snake Boiga irregularis becomes established on the island.

Taxonomic source(s)
Slikas, B.; Jones, I. B.; Derrickson, S. R.; Fleischer, R. C. 2000. Phylogenetic relationships of Micronesian white-eyes based on mitochondrial sequence data. The Auk 117: 355-365.

Taxonomic note
Zosterops conspicillatus (Sibley and Monroe 1990, 1993) has been split into Z. conspicillatus and Z. rotensis following Slikas et al. (2000). In Collar et al. (1994), Z. conspicillatus was split into the extinct Z. conspicillatus, and the extant Z. saypani and Z. rotensis following H. D. Pratt in litt. (1994). Slikas et al. (2000) treat saypani as a subspecies of conspicillatus.

Identification
10 cm. Small, warbler-like bird that moves about in small groups. Yellowish-olive above, saffron-yellow lores and underparts. Bold white eye-ring. Voice Calls and song not well differentiated, include harsh, rolling, low-pitched tsheip, buzzing zee-zee-zeeee, and two-note see-tseep. Hints Quieter and less conspicuous than most white-eyes.

Distribution and population
Zosterops rotensis is endemic to Rota in the Northern Mariana Islands (to USA), where it was once thought to be common and widespread, but is now largely restricted to the upper escarpments of the Sabana plateau (J. Lepson in litt. 1999), where it is found in mature wet forest above 200 m. In 1982, it was estimated to have a population of 10,763 individuals (Engbring et al. 1986). Since then, surveys have estimated 300-1,500 birds (1990) (Craig and Taisacan 1994), 1,165 birds with 94% of the population restricted to four patches of forest covering only 259 ha (1996) (Fancy and Snetsinger 2001), and 1,092 birds (1999) (F. A. Amidon. 2000, Williams 2004). Thus the population has declined by a rate equivalent to 74% over 10 years, however there are anecdotal reports that the population has increased since the 1990s (F. Amidon in litt. 2007, 2010, 2011). From 2005 to 2008 the Rota Sabana region was searched for presence/ absence of white-eyes; they were located in 298 ha spread over 6 primary areas on the Sabana tabletop and ridges between 100m and 490m elevation (L. Zarones in litt. 2012). The recovery plan presents a long-term goal of restoring the population to a stable 10,000 individuals (U.S. Fish and Wildlife Service 2007).


Population justification
The population was esimated at c.1,100 individuals in 1999. This is roughly equivalent to 730 mature individuals.

Trend justification
A decline of 50-79% over ten years (three generations) is estimated based on a decline from 10,763 in 1982 to 1,092 in 1999 (Williams 2004). However, there are recent anecdotal reports that the population may have increased since the 1990s, and as such the trend may be revised following a planned population survey in 2012 (F. Amidon in litt. 2012).

Ecology
Its ecological requirements are poorly known. It may favour native, mature, wet limestone forest (Fancy and Snetsinger 2001), appearing to prefer Hernandia labyrinthica mixed forest and Merrilliodendron megacarpum forest, although this apparent relationship could simply be a factor of its decline in recent decades (Amidon 2000). Within the Sabana region of Rota, it was observed to favour tall limestone forest, and avoid grassland, low limestone forest, and secondary pandanus vegetation types (L. Zarones in litt. 2008).  The species favours forest with more mid-sized stems, more foliage density, more epiphytes, greater total canopy cover, and fewer overal plant species (Zarones et al. submitted). It feeds on insects, seeds, and fruit, and perhaps nectar (F. A. Amidon. 2000). Adults have been observed feeding young and incubating partners on the nest with moths and caterpillars, as well as possibly snails, spiders, beetles, mayflies and katydids (S. Faegre in litt. 2009). Its absence from some areas of apparently suitable native forest (J. Lepson in litt. 1999) is unclear, but may relate to prey availability (Amidon 2000) and/or forest structure (Zarones et al. in review). Nesting has been recorded from December to August, although nest building has been recorded in September, and clutch-size is one to two eggs (Amidon et al. 2004, Berry and Taisacan 2008), though a nest was recently observed with three eggs (F. Amidon in litt. 2007, 2010, 2011). During 2005-2008 the species was located on the Sabana tabletop and ridges in the Rota Sabana region between 100m and 490m elevation (L. Zarones in litt. 2008). The average number of fledglings from successful nests is 1.5 (n = 4) (Berry and Taisacan 2008).

Threats
The recent rapid declines and the current localised distribution are most likely to be primarily a result of habitat loss and degradation owing to agricultural activities, development, typhoons (Fancy and Snetsinger 2001) and use of pesticides (USFWS 2001). The recent introduction of the brown tree snake Boiga irregularis on Saipan is a serious concern. If the snake becomes established on Rota serious future declines are likely (A. Saunders in litt. 2003). Predation by introduced rats Rattus spp. and Black Drongo Dicrurus macrocercus has been implicated in its decline (Craig and Taisacan 1994, Craig 1999): Among eight nests observed during a nest success/predation study one was predated by Mariana Crow Corvus kubaryi during the nestling stage and a nest with eggs was predated by a rat Rattus spp., although in this case the nest may have already been abandoned (Berry & Taisacan 2008). A 2009 study of 18 nests found that 33% of the nests were depredated and the native Micronesian Starling Aplonis opaca is a nest predator (F. Amidon in litt. 2007, 2010, 2011).

Conservation Actions Underway
The species was listed as endangered under the US Endangered Species Act in 2004 and in October 2006 c.1,600 ha of critical habitat was designated for the species (U.S. Fish and Wildlife Service 2004, 2006). The US Fish and Wildlife Service published a recovery plan in 2007 (U.S. Fish and Wildlife Service 2007). Funding was acquired in 2003 to start a nest predation study and experimental trapping of predators observed raiding nests but additional work is still needed (T. de Cruz in litt. 2003). In addition, funding in 2005 was provided to begin a foraging ecology study on the species to help determine reasons for its limited distribution and further work on nesting ecology was conducted in 2009 (F. Amidon in litt. 2007, 2010, 2011). Funding for a snake barrier at the Rota port has also been provided but planning and construction are still in their early phases (F. Amidon in litt. 2007, 2010, 2011). Plans are underway for the population to be surveyed in April 2012 (F. Amidon in litt. 2012). Conservation Actions Proposed
Monitor population trends through detailed censuses (G. Wiles in litt. 1999). Control and monitor population of brown tree snake Boiga irregularis. Control Rattus spp. and D. macrocercus if these are established to present a major threat (J. Lepson in litt. 1999, U.S. Fish and Wildlife Service 2007). Enact the an island-wide Habitat Conservation Plan or similar agreement, including the protection and replanting of native forest in the Sabana region (G. Wiles in litt. 1999). Research its breeding ecology and life history in order to determine its habitat preferences and reasons for decline (J. Lepson in litt. 1999). Assess the need to establish an additional wild population in a predator-free site (U.S. Fish and Wildlife Service 2007). If brown tree snake becomes established the establishment of a captive population will become a priority as an insurance measure against the likely rapid declines that could occur in the wild population. Develop a public awareness and education programme including community outreach activities to involve communities in native forest restoration (U.S. Fish and Wildlife Service 2007).

Related state of the world's birds case studies

References
Amidon, F. A. 2000. Habitat relationships and life history of the Rota Bridled White-eye (Zosterops rotensis). Thesis. MSc, Virginia Polytechnic Institute and State University.

Amidon, F. A.; Haas, C. A.; Morton, J.M. 2004. Breeding biology of the endangered Rota Bridled White-eye. Wilson Bulletin 116: 342-346.

Anon. 2004. Recovery outline for the Rota Bridled White-eye (Zosterops rotensis).

Berry, L.; Taisacan, E. 2008. Nest success and nest predation of the endangered Rota White-eye (Zosterops rotensis). Wilson Journal of Ornithology 120(3): 618-619.

Craig, R. J. 1999. Conservation of endangered white-eyes (Zosteropidae) in the tropical Pacific.

Craig, R. J.; Taisacan, E. 1994. Notes on the ecology and population decline of the Rota Bridled White-eye. Wilson Bulletin 106: 165-1678.

Engbring, J., Ramsey, F.L. and Wildman, V.J. 1986. US Fish and Wildlife Service, Honolulu, USA.

Fancy, S. G.; Snetsinger, T. J. 2001. What caused the decline of the Bridled White-eye on Rota, Mariana Islands? Studies in Avian Biology 22: 274-280.

National Research Council. 1997. The scientific bases for preservation of the Mariana crow. National Academy Press, Washington, DC.

Slikas, B.; Jones, I. B.; Derrickson, S. R.; Fleischer, R. C. 2000. Phylogenetic relationships of Micronesian white-eyes based on mitochondrial sequence data. The Auk 117: 355-365.

U. S. Fish and Wildlife Service. 2001. Additional protection for the Rota Bridled White-eye proposed. 'Elepaio 61: 72.

U.S. Fish and Wildlife Service. 2004. Endangered and threatened wildlife and plants; Endangered Status for the Rota Bridled White-Eye (Zosterops rotensis) from the commonwealth of the Northern Mariana Islands. Federal Register.

U.S. Fish and Wildlife Service. 2006. Draft recovery plan for the Nosa Luta or Rota Bridled White-eye (Zosterops rotensis).

Williams, S. 2004. Endangered and threatened wildlife and plants; endangered status for the Rota Bridled White-eye (Zosterops rotensis from the Commenwealth of the Northern Mariana Islands. Federal Register 69(14): 3022-3029.

Williams, S. 2004. Endangered and threatened wildlife and plants; Endangered Status for the Rota Bridled White-Eye (Zosterops rotensis) from the commonwealth of the Northern Mariana Islands. Federal Register 69(14): 3022-3029.

Zarones, L., Colon, M. R., Ha, J. C., Ha, R. R. Submitted. Effects of foliage-invertebrate availability and forest structure on the abundance of the critically endangered Rota White-eye Zosterop rotensis in Rota, Mariana Islands. Bird Conservation International.

Further web sources of information
Alliance for Zero Extinction (AZE) species/site profile. This species has been identified as an AZE trigger due to its IUCN Red List status and limited range.

Click here for more information about the Alliance for Zero Extinction (AZE)

Explore HBW Alive for further information on this species

Search for photos and videos, and hear sounds of this species from the Internet Bird Collection

U.S. Fish and Wildlife Service - Draft Recovery Plan

Text account compilers
Bird, J., Butchart, S., Calvert, R., Derhé, M., Harding, M., Mahood, S., O'Brien, A., Shutes, S., Stattersfield, A., Symes, A.

Contributors
Amidon, F., Lepson, J., Saunders, A., Wiles, G., de Cruz, T., Zarones, L., Faegre, S.

Recommended citation
BirdLife International (2014) Species factsheet: Zosterops rotensis. Downloaded from http://www.birdlife.org on 29/07/2014. Recommended citation for factsheets for more than one species: BirdLife International (2014) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 29/07/2014.

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

To provide new information to update this factsheet or to correct any errors, please email BirdLife

To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.

Additional resources for this species

ARKive species - Rota white-eye (Zosterops rotensis) 0

Key facts
Current IUCN Red List category Critically Endangered
Family Zosteropidae (White-eyes)
Species name author Takatsukasa & Yamashina, 1931
Population size 730 mature individuals
Population trend Decreasing
Distribution size (breeding/resident) 8 km2
Country endemic? Yes
Links to further information
- Additional Information on this species