Census reveals dips and peaks in breeding seabirds

Cousin Island Special Reserve enjoys a relatively stable population of breeding seabirds according to censuses conducted from 2006 to July 2009. The white-tailed tropicbird (Payanke), in particular has had a stable population since 2006. The Tropicbird mean number was estimated at around 1,000-1,200 breeding pairs in July 2006 and 2009, similar to what was already found 10 years ago in 1999.

Monitoring is done on Cousin for seven breeding seabird species, notably twice a year for tropicbirds and white terns (Golan). Using methodology first developed by Nature Seychelles and used on other Seychelles islands,  censuses are carried out by the wardens and volunteer students on the Island.

Censuses are also carried out for lesser noddy (Kelek)  and brown noddy (Makwa), Audubon’s shearwater (Riga), and bridled terns (Fansen). The estimate of 66,272 pairs of lesser noddy in July 2009 is lower than the population estimates recorded between 2005-2007, probably due to natural inter-annual variations in breeding population and very low breeding success recorded in 2008 attributed to the La Nina weather event. However, it is still comparable to the population estimates recorded between 1999 and 2002. For brown noddy, two annual censuses conducted in July/August 2006 and July 2007 indicated a relatively stable breeding population on Cousin of around 1,860-1,960 breeding pairs.

Seychelles is internationally important for seabirds, with 18 breeding species numbering millions of individuals. For the last 30 years conservationists on some islands have been conducting research programmes and undertaking censuses.  The Seychelles Seabird Group was launched - with backing from the Norwegian Embassy and Airtel Seychelles - with the aim of coordinating this effort. Since its formation partners have collected robust data on seabirds and received practical training of field staff in standardised methods laid out by Seabird Monitoring Handbook for Seychelles.

In other news, Nature Seychelles has recently stepped up its research on seabirds. In collaboration with ECOMAR/University

Geo-locator on a wedgetailed shearwater © Michelle Kappes

of La Reunion, seabird tracking research is starting on Cousin, notably using  geolocators on wedge-tailed shearwater, in order to investigate their foraging range and at-sea feeding grounds. Work under this collaboration began in 2005 as part of a long-term marine research project in the western Indian Ocean. Its aim was to study the feeding, breeding, and population of the main seabird species of the Indian ocean in order to use seabirds as indicators of marine health.

Seabirds, super abundant and widely distributed, are in close interaction with their marine habitats including surface dwelling fish like tuna. For instance, brown noddies and wedge-tailed shearwaters are associated with skipjack tunas. Along with pinnipeds and turtles, they are also the only marine predators accessible from land because they come to breed. Their study gives a window through which we can see what is happening at sea. There is ample proof, for example, that a study of population and migratory patterns of birds that feed on fish are viable indicators of the health of the species they eat. Such research provides data that can be used for marine management.

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