Seychelles White-eye 2016 Census

By December 21, 2016Nature

The Environment department has released the results of the recent Seychelles White-eye census on North Island. The latest count of this endangered endemic bird took place during October 2016 and has revealed that from just 25 birds that were reintroduced in July 2007, there are now estimated to be up to 105 individuals on North Island, around one sixth of the current global population.

The population on North has quadrupled, steadily increasing since their introduction in 2007 until 2014, and from 2014 to 2016 the population appears to have stabilised. This likely indicates that the Seychelles White-eye has successfully occupied all presently available habitat. The population is expected to increase in tandem with the continuous habitat restoration on North Island and the eradication of Common Mynas.

As part of North Island’s intensive Noah’s Ark rehabilitation project, 25 Seychelles White-eyes were released on North Island over a two-week period in July 2007. This small, olive-grey bird identified by a narrow white eye-ring, is currently listed as Vulnerable on the IUCN Red List of Threatened Species and is endemic to only four granitic islands in the Seychelles. The main threat it faces is habitat loss and conservation efforts are focusing on increasing the species’ range in an attempt to make it less vulnerable.

The Seychelles White-eye is important in that it was first listed as Critically Endangered on the IUCN Red List in 1994 and in 1996 it was estimated that only 25 to 35 individuals existed worldwide. In 2005, the Seychelles White-eye was downlisted to Endangered as a result of a previously unknown population that was discovered on Conception Island and a successful introduction to another island in the Seychelles, as well as conservation strategies that had been put in place to conserve all known populations. At the time of their reintroduction to North Island in 2007, the global population was estimated at 350-400 individuals and North Island was deemed an ideal island on which to introduce this rare bird, due to its large size, ongoing habitat rehabilitation and rat-free status.

Since then, a census has been conducted on a regular basis as part of the ongoing project to assess the population size and to capture and fit unringed birds (offspring) with colour rings to enable individual identification. The census is conducted through a variety of scientific methods, such as visual searching, early morning call censuses, listening for contact calls, tape-luring and stationary mist nets to capture them.

The latest count took place during October 2016, with positive results. The population on North Island has increased fourfold since the reintroduction and it is estimated that the current population is between 91 and 105 individuals. The number of groups has increased since 2015 and average group sizes are similar to that reported in 2015. The number of individuals that are known to be unringed has decreased from 24-34 in 2015 to just 13-16. The population is skewed towards younger individuals as was also found in 2015, and the birds were actively breeding during this survey with at least four chicks fledging during this period.

Overall, the North Island Seychelles White-eye population appears healthy and self-sustaining. Since their introduction in 2007, the population has steadily increased until 2014 and between 2014 and 2016, the population appears to have plateaued. This likely indicates that all the presently available habitat has been occupied and that the population size has started to stabilise. This hypothesis will need to be assessed in future surveys.

Large tracts of land have been cleared of alien plants since the previous survey in 2015 and many of these areas have been replanted with indigenous trees and shrubs (read more about coconut clearing here). However, it is likely to take a few years for these new plants to become established and mature to an extent where these areas become suitable for habitation by Seychelles White-eyes. It is expected that the population will increase in tandem with this additional habitat becoming available. At present there is also a dedicated effort to remove Common Mynas from North Island. Although there is no direct evidence yet, predation of nests is viewed as a potentially large threat to the Seychelles White-eye and the eradication of Common Mynas from North Island is likely to have a positive effect on the population.

The positive results of this census have provided scientists with valuable research data which will further assist Seychelles White-eye conservation in the future.

Reference:

PIETERSEN, D. 2016. Assessment of the Seychelles White-eye Zosterops modestus Newton, 1867 population on North Island, Seychelles: Report for the period 10th to 26th October 2016. North Island.