With their long wings, graceful flight, and remarkable mating display, Magnificent Frigatebirds are certainly one of the most recognizable seabirds. They are also considered one of the most threatened seabirds in the West Indies and we still have a rather incomplete understanding of their ecology and breeding system. With more than 1,700 nests counted in 2008, the Codrington Lagoon on Barbuda harbors one of the largest known breeding colonies. It is therefore recognized that this site is important to manage and protect, and Codrington Lagoon has recently been designated as an Important Bird Area, a Ramsar site, and a National Park.
When planning a sail to Barbuda, whether you arrive in the fall when the Frigatebirds begin nest building and the males are displaying, or in the summer when large chicks will look out at you from their nests, the nesting colony in Codrington Lagoon is well worth a visit. The Lagoon, bordered by one of the celebrated long sand beaches on Barbuda’s west coast, shelters several mangrove species that provide a nesting habitat for the birds. It is important to remember to stay a respectful distance from the nests as indicated by the buoy line markers to avoid disturbing nesting birds. Adults who are approached too closely will get nervous and they or other birds may knock an egg or young chick into the water.
Male Magnificent Frigatebirds chasing each other for sticks (nest material) on Barbuda.
In cooperation with the Barbuda Council, the Environment Division, National Parks, and the Environmental Awareness Group, researchers from Canada (PhD student Sarah Trefry and Dr. Antony Diamond) are conducting a project to unravel the mysterious mating system of Magnificent Frigatebirds. This species has several rather unusual characteristics. For example, while in most seabirds males and females look very similar, in Frigatebirds the brown females are larger than the males which are heavily ornamented with shiny black feathers and a red throat pouch that they inflate when performing courtship displays. Like most seabirds, both parents help to raise their single chick. Males collect all of the nest material and females build the nest. Both parents take turns going on multi-day foraging trips for flying fish and squid. However, in an unusual twist, male Magnificent Frigatebirds abandon their chick by the time it is 160 days old, leaving the female to continue to care for a juvenile that is dependent on her for over a year. Presumably the male goes somewhere to moult and recover between breeding attempts. This extended length of parental care raises the question of whether females breed only every second year, since they also need time to moult after nesting, while males breed annually.
Sarah’s PhD project will determine if males and females do have different breeding cycles by wing tagging individual birds and following them through several years. Other aims of the project include determining whether this breeding system results in selection for a larger proportion of females produced relative to males, testing several hypotheses for the evolution of size differences between males and females, and learning where adults forage through wing tags and loggers on the birds’ backs.
Female wearing wing tag and geolocator.
Breeding colonies of Frigatebirds around the world are threatened by the encroachment of human development and the invasive species that so often arrive on islands with such activity. A slow rate of reproduction and colonial breeding exacerbates the extinction risk of seabird species like Frigatebirds. The aims of this project will advance our knowledge of the ecology and movement of Magnificent Frigatebirds, which will inform future conservation management of the species. Specifically, determining whether females are breeding and present on the colony only every other year will enable more accurate estimates of population size.
Male with wing tags.
You can help with this project! If you see a Frigatebird with yellow wing tags, please let Sarah know by email: s.trefry@unb.ca or phone: +1 506 452 6033. Using binoculars or taking a digital photograph can help to read the wing tag and learn more about individual movement patterns.
