Seychelles White-eye news

26-06-2001

Recent research on the biology of the Seychelles White-eye Zosterops modestus has increased our knowledge of this Critically Endangered bird.

The endemic Seychelles White-eye became extremely rare during the early 20th Century and, by 1996, the world population was thought to number just 50 birds confined to the island of Mahé. However, in 1997, a previously unknown population was discovered on Conception, a small abandoned island 1.6 km from Mahé (see World Birdwatch, 19 (2): pp. 20-21).

Recent surveys involving individual identification by colour-ringing, carried out during Phase 1 of a Recovery Programme, have indicated that the population on Conception is around 280 birds. Although birds from the two islands look very similar, the research indicates that there are differences regarding their genetics and body measurements.

Monitoring of breeding birds has revealed some interesting facts. For example, incubation lasts around 13-15 days, and chicks fledge from the nest after a further 11-16 days, continuing to be fed by adults for one to two more months. On Conception, the percentage of successful nests is around two to three times the percentage on Mahé. The main reason for this difference was found to be heavier nest predation on Mahé from introduced Ship Rats Rattus rattus and Indian Mynas Acridotheres tristis, and the endemic Seychelles Bulbul Hypsipetes crassirostris. On Conception, only the less arboreal Norwegian Rat R. norvegicus is present, Mynas are rarer and Bulbuls absent, but even here 39% of nestlings were predated.

Invertebrates, but also a large amount of berries and seeds of both native and non-native trees seem to form essential elements of the diet of Seychelles White-eyes. Habitat preferences have also been determined based on the Conception situation. This information, along with the IUCN Re-Introduction Guidelines, are being used to identify the most suitable islands where, following eradication of introduced predators and consultations with all relevant stakeholders, birds could be safely translocated.

The most extraordinarily discovery about the species, however, is the remarkable and complex co-operative breeding system, a phenomenon apparently unique amongst white-eyes and perhaps other bird species too. On Conception, almost twice the number of adults attend a single nest as compared to Mahé. On the latter island, nesting groups usually produce two eggs per nest whereas on Conception many nests contain between two to seven eggs. Large breeding groups are formed, with several females laying in the same nest and more than one singing male present. In addition, the individual composition of large nesting groups often changed between nesting attempts, even within the same breeding season, with regular swapping of individuals between neighbouring groups! Such peculiar social organisation clearly warrants further detailed investigation for which funding is being sought. The researchers would also be grateful to receive information (including reprints) on similar complex co-operative breeding passerine systems that have been studied elsewhere.

The next Phase of the Seychelles White-eye Recovery Programme (SWERP) began in November 2001 and consists of implementing management recommendations on Conception and Mahé, preparing a Recovery Action Plan with all stakeholders and planning for translocation of birds to suitable predator-free islands.