The ‘gular pouch’ of the male frigatebird is truly weird looking, inflated in the breeding season to attract a female, making it look rather like some sort of seabird-frog hybrid when showing off. There are only 5 species of frigatebird in the world, so the return of the endemic and iconic Ascension frigatebird to the island from which it took its name was a good news story that should not go unnoticed.
The frigatebird originally deserted the main island of Ascension as a breeding site after the introduction of cats in 1815 that had been used to control a burgeoning population of rats. Unfortunately many of the cats went feral and found Ascension’s nesting seabirds easier to catch and more palatable than rats, driving many species onto inaccessible offshore stacks. Although the last feral cats were eradicated in 2004 it took until late last year for the first pair of frigatebirds to successfully nest on the main island, despite many other species returning soon after the eradication. Why it took frigatebirds longer to recolonize the island and what will encourage greater numbers to return is currently unclear. Frigatebirds are a colonial-nesting species so the lack of an established mainland nesting colony to act as a nucleus for new breeding pairs is potentially a limiting factor. In 2011 Ascension Island Government (AIG) Conservation and the RSPB established two dummy frigatebird nesting colonies, consisting of plastic decoys with recorded mating calls, in an attempt to coax the birds back to the mainland. There was little activity until December 2012 when two pairs of frigatebirds were found nesting on a remote area of the Letterbox Peninsula – ironically well away from the decoys.
“The challenge now is to build on this small success and create the conditions necessary for frigatebirds to recolonize more of their former breeding range.” Says Dr Sam Weber, one of the Darwin Research Fellows.
Initially two pairs of birds were found incubating eggs in close proximity to one another. Unfortunately one of these nesting attempts failed, but the other pair is rearing a very healthy-looking chick. The nest site is visited periodically and is continually monitored by cameras so that the chick’s progress can be followed. “We hope that we will soon be able to announce the first fledged chick to leave the main island in living memory!”.
The frigatebird tracking project that is currently being carried out by the University of Exeter, University of Lund – Sweden, AIG Conservation Department and the RSPB is part of a Darwin Initiative-funded project to develop and implement a Biodiversity Action Plan (BAP) for Ascension Island. As the only remaining endemic bird on Ascension, the frigatebird is a priority species for the BAP and for conservation on the island in general. The current research aims to study the movements and behaviour of the birds at sea with a view to identifying important foraging grounds and highlighting potential conflicts with fisheries. In addition to the frigatebirds, researchers are working on tracking a number of other marine species around Ascension Island, including masked boobies, hawksbill turtles, green turtles and sooty terns. It is hoped that by combining these tracking data, a holistic picture of important areas for wildlife can be developed which will help inform the designation of marine protected areas in the future.
Even from the small number of tracking devices deployed so far, researchers are beginning to build a picture of the massive distances that frigatebirds routinely travel from Ascension Island in search of food. Napoleon, a male frigatebird carrying a PTT satellite tag, is just returning from a foraging trip from the coast of Ascension Island, that has taken him over 1000km –more than the distance from Falmouth to Dundee by road. Since the tag was attached in February he has travelled a staggering 7860 km!
“I think the results have come as a surprise to many people on the island who are used to seeing frigatebirds soaring over the coast and catching hatchling turtles on the beaches, but had no idea just how far afield they roamed.” Says Dr Weber.
In addition to demonstrating the impressive distances travelled, the results are also revealing the considerable area used by frigatebirds for foraging, with no particular hotspots emerging. These findings mirror the results of tracking work being carried out on masked boobies at Ascension Island. One hypothesis is that the absence of predictable food patches in the deep sea, with no fixed oceanographic features such as banks or upwelling zones to concentrate biological productivity, forces the birds to adopt a broad searching strategy. Whatever the explanation, these findings highlight the difficulties of delineating fixed protected areas in the open ocean.Based on trials to date, the team has plansto deploy a new type of tracking device in September that will record GPS-quality positional data that can be downloaded remotely from the mainland. The tags are attached to the tail feathers of the bird using an adhesive tape and will drop off naturally as the feathers are moulted. This system will allow them to study the movements of individual birds over long periods, including fine scale movements, such as foraging behaviour and possible interactions with fishing vessels, without the need to subsequently recapture the animal.
“We hope that now some breeding pairs have returned they will act as a catalyst for more nesting on the main island in future.” Adds Dr Nicola Weber, also a research fellow on the project. There have been other frigatebirds roosting in the vicinity, and it is possible that competition for nesting space on the small offshore stack that is currently the frigatebirds sole breeding site will ultimately drive more pairs back to the main island. The Ascension frigatebird is not in any immediate danger of extinction as its major nesting colony remains out of the reach of both people and predators. However, the future of the mainland colony is still very tentative. The return of a breeding pair to the island could just be a ‘freak event’ or it could herald the start of a larger recolonisation. However, the passion of the researchers driving the project forward is clear, and with them fighting for the islands safety, frigatebirds and other species alike are sure to reclaim at least part of the island as their home and breeding ground soon enough.
Article compiled by Roz Evans based on contact with Sam and Nicola Weber.
Dr Sam Weber and Dr Nicola Weber are the Darwin Research Fellows for the Darwin Initiative project “Designing and Implementing a Biodiversity Action Plan for Ascension Island” that is being jointly run by the University of Exeter and Ascension Conservation Department. Both Sam and Nicola studied their MScs and PhDs at the Centre for Ecology and Conservation, University of Exeter Cornwall Campus, before starting on this project.
The progress of all 3 birds carrying satellite transmitters can be watched in near real-time at http://www.seaturtle.org/tracking/?project_id=809.
For exciting updates on the work that the Ascension Island Government Conservation Department are carrying out then please visit their Facebook page: www.facebook.com/AscensionIslandConservation or follow them on Twitter @AIGConservation. Their website is currently under construction and the link for this will be posted on these social media sites as soon as it goes live.