Monday, 27 July 2015

Conservation Updates: Denis Private Island

Green Islands Foundation completes eradication of invasive Myna birds on Denis Private Island

The Common Myna, also known as Indian Myna, is one of the world’s most invasive birds, causing problems wherever it has been introduced. Myna birds are not native to Seychelles, but since they were introduced here from Mauritius in the 19th century, they have spread to many of the islands. Because their diet includes the eggs and chicks of other birds they pose a threat to endemic birds in Seychelles. 

 Therefore Green Islands Foundation (GIF) has been removing Mynas from Denis Island, where four species of endemic birds have been introduced in the past to save them from extinction. 

Mynahs caught in a cage
Using trapping and shooting, GIF has been able to eradicate all Mynas, initially estimated to be just over 1000 birds, from the island and can now report that the last known Myna bird has been shot last weekend. This major milestone suggests that Denis Island, as one of the few islands in the world, has been successful in the removal of a large population of these smart and cunning birds. Early observations show that many of the other bird species on the island have been flourishing since the Myna eradication began (in 2010), and GIF will be monitoring the effect of complete eradication over the coming years.

Denis Island as safe haven for endemic birds

A pair of Seychelles Magpie Robin
In the early 2000’s Denis Island, with its mixed and rich broadleaved woodland,  was considered one of the most suitable islands to act as a refuge for some of Seychelles' endemic birds (= birds occurring only in Seychelles and nowhere else in the world) that were threatened with extinction. In 2001 and 2002 cats and rats were eradicated from the island and large parts of the forest were transformed into suitable bird habitat. This allowed the translocation of the Seychelles Fody and Seychelles Warbler in 2004, followed by the Seychelles Magpie Robin and Seychelles Paradise Flycatcher in 2008. 

However, it seemed that the conditions were not optimal, as the bird populations grew more slowly than expected. The presence of Mynas appeared to be an important reason for this slow growth.

The threat of Mynas on Denis Island

An injured Warbler
Studies done on Denis Island showed that Mynas indeed behaved aggressively towards the endemic birds. For example, the Seychelles Warbler Research Group (University of Groningen, the Netherlands) found that many female Warblers had severe head wounds. Those were caused by by Myna attacks when parent Warblers were incubating eggs or brooding chicks on the nest. Similar head wounds were also found on Seychelles Fodies and Seychelles Flycatchers. Mynas also destroyed eggs of all of the endemic species, and chicks were found thrown out of the nest of Magpie Robins. 

The Mynas even stole the breeding sites of the Seychelles Magpie Robin by occupying the nest boxes that were put up for them in the trees! Because of these problems, Green Islands Foundation started a GoS-GEF-UNDP-funded project to remove the Myna birds from Denis Island, with the full support of the Ministry of Environment. According to the Denis Island environment manger, Janske van de Crommenacker: ''The Seychelles Paradise Flycatchers are still critically endangered, and thus it is extremely important to provide a safe environment for them and the other endemic birds. A home that is free of any predators that are brought in by man''. In 2010 GIF contracted WildWings Bird Management (WWBM, UK) to plan and implement the project, using volunteer postgraduates to undertake the bulk of the work after a period of training by WWBM’s Prof Chris Feare and his assistant.

The project

P-A Ahlén in camouflage
At the start of the eradication, decoy traps, comprising a central compartment containing a live decoy Myna and four outer catching compartments, proved to be by far the most suitable technique for catching Mynas on Denis Island. In total, between 2010 and 2015, volunteers and students caught over 1100 birds using decoy traps (95% of the total catch!). Towards the end of the eradication, when the few Mynas left were unwilling to enter the decoy traps anymore (trap-shy), P-A Åhlén was recruited, an expert conservation hunter from the Swedish Association for Hunting and Wildlife Management. Endorsed by the Seychelles Police force, he shot 66 of the remaining Myna birds on the island and he left when no more Mynas were known to occur on the island. Over the last three months, Denis Island environment staff together with GIF volunteers monitored the island for signs of Mynas and found one remaining bird, which was observed for several weeks to find out if it attracted any other birds hiding on the island, but no other Mynas were seen. 

This last bird was shot by the team last weekend, concluding this important Myna eradication project. Although one can never be 100% certain that a Myna is not hiding in the forest, Green Islands Foundation feels confident that the threat of Mynas on Denis Island has been successfully averted.

Positive impacts of the eradication

An endangered
Paradise Flycatcher
In the years after the Myna eradication project was started, population surveys of the translocated endemic birds revealed staggering results. As can be seen in the graph, a large number of Mynas was removed from the island very early in the eradication in 2010-2011, and the population of Magpie Robins doubled and Paradise Flycatchers tripled in just three years! This result suggests that the removal of Mynas from the island is already having a major positive impact on the endangered birds that now call Denis Island their home. “A lot has happened on the island since the Myna eradication began, endemic bird populations are increasing and the behaviour of the birds on the island also seems to be changing. Some birds are seen out in the open more often than before, suggesting that without the threat of being attacked by Mynas the endemic birds can move freely around the island” according to GIF general manager Arjan de Groene.

The future

Chart depicting the positive effects
of Mynah eradication on
Denis Private Island
Green Islands Foundation and Denis Island will continue to monitor for the presence of Mynas and will remove any new invasions as soon as they are seen. Other species might now choose Denis Island as their home or breeding ground: last year, Lesser noddies were found nesting on the island in small numbers, for the first time. It may be coincidence, but time will tell whether other surprising, unexpected effects will be found now that the Myna is no longer present to interfere with the natural order of things... We will keep you posted! In the meantime GIF wants to thank wholeheartedly the enormous contribution of the volunteers, Denis Island staff and management who have made this possible.

An educational video sponsored by GoS-GEF-UNDP and explaining the project in more detail can be found by CLICKING HERE.

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