Justification of Red List Category
This species appears to have declined as a result of predation by introduced rats, exacerbated by habitat destruction and degradation through invasion of exotic weeds. Formal surveys have failed to find any in the last two decades. There have been a number of other reports during 1978-2005, however a three-week survey in 2009 failed to find the species and estimated a 90% chance that the species is functionally extinct (Dutson 2013). A tiny population may however remain and therefore it is treated as Critically Endangered.
The remaining population is assumed to be tiny (fewer than 50 individuals and mature individuals), with only scattered sightings since 1978.
The species is considered to have declined as a result of predation by introduced rats, exacerbated by habitat destruction and degradation through invasion of exotic weeds.
Zosterops albogularis is endemic to Norfolk Island (to Australia). It was reported as very plentiful by Hull (1909) and 12 specimens were taken in one week in 1926 by Correia. However, the population is thought to have fallen below 50 individuals by 1962 (Mees 1969), and by the 1970s it had become confined to weed-free indigenous forest in and around the Norfolk Island National Park. Although formal searches have failed to find any in the last three decades, there have been scattered sightings throughout this period (Schodde et al. 1983), including one in 1987, two in 1991, four in 1994 and one in 2000. Since then a number of unconfirmed reports have been logged from the Norfolk Island National Park, most recently in 2006 (B. Watson in litt. 2006, G. Dutson in litt. 2009, 2010). The remaining population, if any exists, is likely to be very small; a comprehensive three-week survey in November 2009 based on 353 point counts failed to find the species and concluded there was a 90% chance that it was functionally extinct (G. Dutson in litt. 2009, 2010, Dutson 2013).
It appears to occur mostly in weed-free indigenous forest, feeding high in shrubs and trees. However, there are old records of it nesting in orchards (Hull 1909), in red guava Pisidium cattleianum trees, and feeding on olive fruits (Mees 1969).
The principal threat is probably predation by black rat Rattus rattus, which is thought to have been introduced in the mid-1940s. The effects of predation have been exacerbated by the clearance of much native forest and invasion of the remainder by exotic weeds. As a result, favoured habitat has been reduced to less than 1% of the area of the island. Competition from the self-introduced Silvereye Zosterops lateralis, which was first recorded on the island in 1904, may also have contributed to the decline, and recent drought years may have stressed the population further (R. Ward in litt. 2006). Predation by feral cats Felis catus may also be a threat. The species may be vulnerable to climate changes and appears to fare poorly during dry years.
Conservation Actions Underway
CITES Appendix I. Surveys were carried out for the species, without success, in 2009 (G. Dutson in litt. 2012). Rat baiting, cat trapping and control of other invasive plants and animals is occurring in Norfolk Island National Park. Responsible cat ownership is being encouraged through sponsorship of cat neutering clinics. The species is being considered in a multi-species management plan for Norfolk Island National Park. A predator exclusion fence was proposed for Norfolk Island National Park to create a predator free island within the park (B. Watson in litt. 2006), but this idea hasn't gained traction, likely due to the costs and maintenance involved (M. Christian pers. comm. 2016). The Australian commonwealth has recently rated Norfolk Island very high on its list of the Australian islands in which they are considering the eradication of invasive rodents, with a possible $20 million investment in the chosen islands over a number of years (M. Christian in litt. 2008).
13-14 cm. Medium-sized, warbler-like bird. Sexes similar. Bright green head, olive-green back, clear white underparts and white eye-ring. Similar spp. Distinguished from other White-eyes Zosterops spp. by large size and white underparts.
Text account compilers
Calvert, R., Symes, A., Garnett, S., Bird, J., Hermes, C., Derhé, M., Khwaja, N., McClellan, R., Stattersfield, A.
Ward, R., Watson, B., Dutson, G., Holdaway, R., Christian, M.
BirdLife International (2020) Species factsheet: Zosterops albogularis. Downloaded from http://www.birdlife.org on 06/08/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 06/08/2020.