New discovery by Island Conservation Society at St. François


06-May-2013

A Shearwater chick on St. François

This is the most southerly population known in Seychelles. The last known report of the birds breeding at St François was when  Desiré Gendron was manager at neighbouring Alphonse from 1951 to 1959. The discovery has been made by Island Conservation Society (ICS) trustee Ralph Meyer-Rust and his partner Sharon Theron during a recent four-day expedition to the uninhabited island.

ICS established a conservation centre on Alphonse in February 2007 and a previously unknown breeding population of shearwaters was found on the island shortly thereafter. ICS followed up with a similar discovery at Desroches. It was long considered a strong possibility that St François also still held a population but a series of daytime searches failed to locate any burrows. This was not too disheartening, considering adults feed offshore during the daytime, only returning to land after nightfall. The final solution to the question could only be found by making an extended overnight visit during the breeding season.

Wedge-tailed Shearwaters breed throughout tropical and subtropical latitudes of the Indian and Pacific oceans. In the granitic islands of Seychelles, birds breed at rat free sites, including Aride, Cousin and Cousine. In the outer islands, they breed throughout much of the Amirantes but are rare visitors further south. Wedge-tailed Shearwaters feed over regions of deep water (often 3,500-4,500 metres) avoiding shallow waters of continental and oceanic shelves. Studies by ICS at Aride have shown they forage further offshore than any of the ten seabird species breeding on the island, associating with predators - mainly tuna -which chase juvenile goatfish, squid and other prey. They are proficient divers, and studies at Cousin have shown they can reach depths of up to 66 metres.

In order to find the St François colony it was essential to know the habits of the birds. Wedge-tailed Shearwaters are colonial breeders, excavating deep cavities in which a single egg is laid. In the breeding season, birds feed offshore during the daytime, visiting land between dusk and dawn. On land, they give eerie calls, beginning about one hour after sunset and continuing until midnight, then resuming between about 3am and 5am. Most breed during the northwest monsoon, laying September to October.

The discovery of the Wedge-tailed Shearwater colony on St. François was the result of a dedicated ICS survey, focused on the collection of data from nesting turtles and a number of key bird species on the island.  Due to the turmoil of a tropical depression over the region during the study, locating the cunningly hidden nesting burrows of potential shearwaters proved a challenging task. 

Numerous sweeps along both the beachhead and past sheltered backwaters proved unsuccessful.  At night, springtide and weather conditions made for less than ideal acoustic conditions. 

On the fourth night, the faint and mournful calls of a number of Shearwaters were recorded in the dense brush bordering a steeply eroded beach-face, to the south of the island.  A closer and careful inspection revealed the presence of six active nesting burrows, with further vocalisations clearly indicating at least two more sites, deeper into the impenetrable scrub.  Some adults, although briefly observed scuttling through the tangled roots and branches, proved extremely reticent. Two visible and partly exposed chicks were successfully photographed. After noting relevant GPS coordinates, this valuable site was not disturbed any further. 

Populations have been strongly persecuted in the past and poaching is still a threat, even at protected islands. Conservationists have also expressed concern that tuna catches in the Indian Ocean may impact on Wedge-tailed Shearwaters, given its close feeding association with this species.More detailed research into the breeding status of Wedge-tailed Shearwaters on St. Francois is required - although the absence of rats and other predators on the island (discounting the presence of crabs and other, opportunistic birds) should bode well for the future viability of this particular breeding colony.

Ralph Meyer-Rust, Sharon Theron and Adrian Skerrett from the Island Conservation Society

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