Christmas Island frigatebird
AUSTRALIAN CONSERVATION STATUS (EPBC Act)
The Indian Ocean and South-east Asia
Christmas Island frigatebird
Tropical waters and emergent trees of the canopy layer on Christmas Island, preferentially in the lee of the wind
AROUND THE WORLD, frigatebirds have gained an honourable reputation among sailors and explorers because of their spectacular appearance and distinctive behaviour. English mariners named them ‘man-o-war’ in the Caribbean, and early sailors described them as the pirates of the animal kingdom worlwide.
Like others in the family, males of the Christmas Island frigatebird (Fregata andrewsi) sport a remarkable red-hued gular pouch, used to attract females. The species is distinguished by its long and narrow wings, brownish-black plumage, long hook-shaped bills.
Frigatebirds didn’t get this pirate reputation just because of their appearance: they are extremely agile while flying, enabling them to steal other seabirds’ catch. Called kleptoparasitism, the behaviour is seen when birds harass other foraging seabirds, using sharp talons and beak to bully them until they are forced to give away their food.
The Christmas Island frigatebird is one of the five frigatebird species in the world and it is endemic to Christmas Island in the Indian Ocean. Oddly, the species shares the island with its relatives, the lesser and great frigatebirds, which are widespread across the tropics.
There are few distinctive features that can help to differentiate these species apart. For instance, Christmas Island frigatebirds have white belly patches and longer white underwing spurs than its relatives.
Frigatebirds have a poor ability to take off from flat surfaces because of their extremely long wings in comparison to their body size, which is why they never land on water.
Despite being a poor swimmer and lacking waterproof feathers, the Christmas Island frigatebird disperses widely offshore, snatching its prey directly from the ocean surface (when it doesn’t steal from other birds) and using its long hooked-bill to feed on planktonic crustaceans, fish and squid.
This magnificent seabird can be found widely around the Indian Ocean and South-east Asia, and it is an occasional visitor to the shores of the Indonesian Islands, the Northern Territory coast, and the Cocos (Keeling) Islands. However, it always returns to mate on its one-and-only breeding ground on Christmas Island.
During the mating season, males display their most attractive feature by inflating their red, heart-shaped gular pouch in order to attract females flying by from nest sites on the canopy. A fascinating courtship takes place once females land near males, which drum on their pouches in order to increase their attractiveness.
Females breed only once every two years and lay one single egg clutches, which makes it difficult to overcome external pressures from human settlement on the island and offshore territories.
Threats to the Christmas Island frigatebird
Since the first visit to Christmas Island and the early settlers of the 18th century, the endemic frigatebird numbers declined rapidly, from an estimated 6200 breeding pairs in the 1890s to about 3300 in the 1940s.
Even though 63per cent of the island’s 135sq.km is national park, around 25 per cent of the island’s rainforest has been cleared for phosphate mining, which has caused one major nesting site to be abandoned. As a result, breeding pairs have continued to decline to about 1200 in 2005 and kept declining over the last decade.
In addition to habitat degradation and phosphate dust covering the forests of Christmas Island, settlement has brought many unwanted exotic species such as cats, rats, and the yellow crazy ant (Anoplolepis gracilipes), which prey on nests and occupies 15 to 18 per cent of the island.
In 2004, the National recovery plan for the Christmas Island Frigatebird was developed but proved unsuccessful. Funding from the Australian Geographic Society went towards research that is being used to help implement a new recovery plan.