Mauritius olive white-eye  (Zosterops chloronothus)

Classified as Critically Endangered (CR) on the IUCN Red List (1).

The Mauritius olive white-eye is perhaps the least well known of the eight threatened terrestrial bird species remaining on the island of Mauritius (3). A small, rather drab bird, it is olive-green above, with paler underparts that become more cream on the belly and yellow on the vent. The olive colouration and a conspicuous white eye-ring help distinguish this species from the related Mauritius grey white-eye, Zosterops borbonicus mauritianus (2) (4). The Mauritius olive white-eye has a long, slender, downward-curving beak (2) (4), said to be longer than that of any other white-eye (5). This species has a warbled song and calls with a metallic plik plik (2) (4).

The Mauritius olive white-eye is endemic to Mauritius, where it occurs in a small area in the southwest of the island (2) (4) (6). Individuals have also been translocated to the small offshore island of Ile aux Aigrettes (2) (6).

The Mauritius olive white-eye is found in wet native upland forest and scrub (2) (4). High densities are thought to occur where small plantations of exotic trees, which may have lower nest predation, are interspersed with native vegetation, used for foraging (2).

The Mauritius olive white-eye uses its long, slender beak to probe into flowers and feed on nectar, and may travel considerable distances to productive flowers (2) (5). Some introduced plants are reported to have become important nectar sources for this endemic bird (2). The diet may also be supplemented with insects (2) (5).

Favoured flowers or nesting sites may be aggressively defended against other individuals, and against the Mauritius grey white-eye (2). Little information is available on the reproductive behaviour of the Mauritius olive white-eye, but recent studies have shown breeding success to be extremely low, with very few young fledged. It is not known whether this is usual for the species, or whether other factors, such as reduced food availability, are negatively affecting reproduction (7). Clutch size is between one and three eggs (2).

Like many native species on Mauritius, the Mauritius olive white-eye has been badly affected by habitat loss and by predation by introduced mammals. The species has a very small range, and its habitat is continuing to decline in extent and quality, compounding the major threat of nest predation. As a result, the Mauritius olive white-eye population has declined drastically since the mid-1970s, from around 350 pairs to only 100 or so in 2001 (2) (3) (6). In addition, the extremely low reproductive success recorded in recent years is of critical concern (7). With such a small population, the species is also particularly vulnerable to extinction from extreme events such as cyclones.

The Mauritius olive white-eye is protected by law, and part of its range occurs within the Black River National Park. There are also plans to purchase habitat around Bassin Blanc (2). In 2005, a species recovery programme was initiated by the Mauritian Wildlife Foundation, with the aim of increasing knowledge of the Mauritius olive white-eye and its threats, and to investigate management techniques. Since then, an intensive management plan has been applied to the species, involving monitoring of the wild population, undertaking predator control at nest sites, rescue and harvest of wild nests, artificial incubation, and hand-rearing of offspring. However, it is thought that effective habitat management and releases onto predator-free islets are more viable options than captive breeding (2) (6).

On the mainland of Mauritius, rehabilitation of the native vegetation is underway in order to improve food sources for native birds, and there are plans to develop Conservation Management Areas with high densities of nectar-producing plants and where predators are strictly controlled. Between 2006 and 2007, a number of Mauritius olive white-eyes were released onto the predator-free, restored islet of Ile aux Aigrettes. This new population has been closely monitored and has been provided with supplementary food, and in 2008 at least two breeding pairs were recorded (2) (6). Other recommendations include studies into the species’ ecology and habitat requirements, providing artificial nectar feeders, and measures to try and increase breeding success (2) (3) (7). It has been found that nest predation is lower in areas dominated by introduced conifers such as Cryptomeria and Pinus (3) (8) (9), suggesting that the role of non-invasive exotic trees in the survival of the Mauritius olive-white eye should be further investigated (3) (9).

View information on this species at the UNEP World Conservation Monitoring Centre.

For more information on the conservation of the Mauritius olive white-eye, see:

• BirdLife International Preventing Extinctions Programme:
  http://www.birdlife.org/action/campaigns/species_champions/index.html
• Mauritian Wildlife Foundation:
  http://www.mauritian-wildlife.org/
• Durrell Wildlife Conservation Trust:
  http://www.durrell.org/Animals/Birds/Mauritius-Olive-Whiteeye/