St. François Research Expedition: Discovering Secrets of Red-footed Boobies and Greater Frigatebirds
By Alphonse Group Conservation Officer, Gail Fordham
The objective of our mission was to capture roosting seabirds on St François island and attach satellite tracking devices to them – quite a unique undertaking, as most tracking studies have focussed on breeding colonies where it is possible to check the attachment of the device and even retrieve it at a later date. Studying a non-breeding colony presents more of a challenge, but the resultant data should provide insight into their flight movements and the secrets of their preferred feeding grounds at sea.
In the darkness, we walked through the maze of mangroves inside St. François lagoon; circles of light from our headtorches illuminating the murky water through which we waded. Every direction we shone the torches, mullet leapt from the water in surprise, and we considered what other creatures were surely lurking around us. Two conservation biologists and consultants, ICS board member, Dr. Gerard Rocamora, and former Alphonse Conservation Officer, Josep Nogués, had arrived from Mahé to the Alphonse ICS offices the day before and spent the afternoon intently checking and testing the devices. Conservation Ranger Chris Narty, George Curd and myself (the current Alphonse Conservation Officers) joined them in this seabird expedition to St François.
As marine protected areas (MPAs) are being planned and designated across the Seychelles via the Seychelles Marine Spatial Plan, research looking at the movements of species and their important foraging locations is vital. It is important that from an ecological perspective, the coverage of protection is meaningful and not arbitrary. Investigating habitat use for various species can help us improve MPA design. With all of this in the back of our minds, we pushed on through the lagoon, carrying an assortment of ladders, poles and rope which would assist us in catching seabirds, the ecology of which we wanted to investigate. In the early evening, we had counted approximately 20,000 Red-footed boobies (Sula sula) – known as Fou Bet in Creole - flying in from the West. Watching the swirling mass of birds begin to settle over St. François, we hoped they would roost low down to make our fieldwork a little easier. In 2017, ICS staff estimated an astonishing 250,000 Fou Bet that covered the entire islet. The two experts believe this exceptional number may have been reached due to the temporary displacement of birds after the strong winds linked to the devastating cyclone Fantala that affected much of the region, including the Aldabra group, where huge numbers of these boobies breed.
Even at our campsite, the Fou Bet filled the trees like decorations, competing for the most comfortable roost spots and arguing in hoarse rasping croaks. Over the first two nights, working until early in the morning, we successfully caught several birds and carefully attached the small devices. The method for attachment depends upon the target species. For the Greater Frigatebirds (Fregata minor) – known as Gran Fregat in Creole - we used a simple harness which strapped around the bird’s chest and wings and under its armpits. The Fou Bet require a more complicated procedure; as these birds are divers, the device needs to be robust against impact with water. The four middle tail feathers are selected, and the satellite tracker is taped to these, with care given to the solar panel which needs to be left completely exposed for this technology to have the best chance of transmitting properly (we are expecting to get around six weeks’ worth of movement data for these birds). We are expecting a longer duration of transmission - up to six months or more - to come from the Gran Fregat, as they are unable to dive for their food due to a lack of oil in their feathers, relying instead upon surface fishing and piratical attacks on other species to steal their catch. ICS monitors seabird populations closely in the islands that fall under its mandate, as they are important indicators of the overall ecosystem health.
On the third night, we heard a Tropical Shearwater (Puffinus bailloni) appear out of the vegetation and swoop over our heads. This species is occasionally seen at sea; however, this is the first record for St. François Island. This observation could be an indication of nesting, and will be investigated on our next overnight visit. On the fourth night, we had an encounter with another lagoon resident. While wading waist-deep, a Sicklefin Lemon Shark (Negaprion acutidens) around 2.5 metres in length came in to inspect the team, before moving back off into the dark. These lagoons and mangrove forests provide ideal nursery conditions and it is possible to observe Lemon Shark pups circling in the shallows.
During the last nights, we spent time capturing and ringing more Red-footed boobies in order to collect over thirty individual blood samples. This will serve for an analysis conducted at the University of La Réunion to determine the genetic affinities of the boobies roosting on St François. This should help us to answer one of the research questions of the tracking study; to determine from which breeding colonies the Red-footed boobies roosting on St François come from. Soon after this expedition, the resident ICS team discovered for the first time ever - a Red-footed booby nest, with a chick estimated at just a couple of weeks old. If other birds follow suit, then St. François could become the fifth island in the Seychelles to host a breeding colony for this species.
St. François, part of the Alphonse Group and at the southern tip of the Amirantes chain, is one of the few wild places left on earth, where creatures can take refuge from the brutality of human impact elsewhere. All 8 tracking devices were successfully deployed on roosting Fou Bet and Gran Fregat, and now we wait to see where the birds travel over the coming weeks. This information will illuminate an area of seabird ecology that is still poorly understood at this location, and will prove useful in the determination of effective MPAs.
Island Conservation Society