Improving the efficiency of rat control is vital to protect the critically endangered Mauritius Olive White-eye (Zosterops chloronothos) and sustain its population in the Black River Gorges National Park. In line with BirdLife International’s global conservation strategy to Save Species, BirdLife’s Partner in Mauritius, the Mauritian Wildlife Foundation has introduced the use of self-resetting traps to preserve the highly endangered bird endemic to Mauritius.

The Mauritius Olive White-eye is estimated to have an extremely small population that continues to decline rapidly due to predation by mammals such as rats that have been introduced in their habitats. The species also has a very small range as  its habitat is declining in quality and extent. It feeds on nectar, fruit and insects, and travels considerable distances to feed on nutritious flowers. The species has long been protected by law and the Black River Gorges National Park partly covers the species’ distribution.

Surveys conducted over three years with HSBC as main sponsor indicated that there are 180-270 of these birds in the Black River Gorges National Park and surrounding areas, but this population was not increasing significantly, as a result of rats preying on the bird’s eggs and chicks. In 2016, The Mauritian Wildlife Foundation (MWF) received a grant from the British Birdwatching Fair (Birdfair) and the Royal Society for the Protection of Birds (RSPB) to finance a research project on rat control methods.

Rats (Rattus spp.) are known to be a major threat to the survival of more than half of Mauritius’ fauna and MWF recorded during the surveys that the Olive White-eye’s breeding is low when rats are not controlled, with below 10% of eggs fledging birds. Several techniques have been applied in the past to control the rats, including use of anti-coagulant poison, such as raticides in territories where rats breed or around trees where the Olive White-eyes are nesting. Up to 72% of eggs laid successfully fledge birds when using the poison grid. However, poisoning is time consuming and costly and can affect other wildlife unintentionally. There is also  the growing evidence that the persistence of poisons has adverse effects on the environment.

Conservation agencies now recommend limited use of poisons and the need to replace them with non-toxin alternatives, especially when used on long-term basis. Very few non-toxin alternatives are known to be cost and time effective. The new technology of self-re-setting traps offers a possible and more humane solution. The traps were introduced in the Island nation of Mauritius in August 2016, and MWF was able to purchase and install the Goodnature® A24 traps for testing. The 15 traps were designed in New Zealand, a country that leads in rat management and installed on various sites.

After one year of testing the traps in the Mauritian habitat, it has been found that these traps offer an effective method of controlling rats in the protected area as opposed to poisoning. Using this technology also saves valuable staff time. MWF is now testing the efficiency of these traps on a much larger scale over a long term to protect the Mauritius Olive White-eye and other endemic birds from rats.

MWF is also monitoring the wild population of the Mauritius Olive White-eye, as well as the breeding success of the population that was translocated on Ile aux Aigrettes where about 50 Olive White-eyes have been identified to compare with nests in the Black River Gorges National Park. MWF will also refine the population estimates by ringing birds on the mainland, when possible, and maintain a 100% ringed population on Ile aux Aigrettes to facilitate population monitoring.