Frigatebirds are also referred to as “frigatebird”, “frigate-bird”, “frigate”, or “frigate-petrel”. These birds are from a family of seabirds called Fregatidae, located throughout all tropical and subtropical oceans.
These five extant species are classified in a single genus, Fregata. The frigatebirds are capable of soaring for weeks on wind currents.
They spend a good part of the day in flight foraging for food and sleep on trees or cliffs at night. Frigatebirds are referred to as kleptoparasites as they steal other seabirds for food on occasion, and are also known to snatch seabird chicks from their nest.
Three of these birds’ five extant species are widely distributed. They include the magnificent, great and lesser frigatebirds. The remaining two species “Christmas Island and Ascension Island frigatebirds” are endangered.
As a result of their conservation status, their breeding habitats are confined to one small island each. The most ancient fossils can be dated to the early Eocene, around 50 million years ago. A frigatebird can sleep during flight.
Their lifespan remains uncertain, but one bird on the Tern island was older than 37 years while another was said to be up to 44 years. So, the safe claim is that the frigates have a long life span.
The species of the frigatebird include:
|Fregata magnificens||Magnificent frigatebird|
|Fregata aquila||Ascension frigatebird|
|Fregata andrewsi||Christmas frigatebird|
|Fregata minor||Great frigatebird|
|Fregata ariel||Lesser frigatebird|
Frigatebirds are slender birds with primarily black plumage. It has five species that are very similar in physical appearance to each other.
The biggest specie is the magnificent frigatebird with a body length of about 45 inches in length. Three species excluding the lesser frigatebird are nearly equal to the magnificent frigatebird in terms of body size. The lesser frigatebird is the smallest with a body length of about 27 inches.
Frigatebirds are conspicuously sexual dimorphic with the females being considerably larger and weighing up to 25% heavier than the males.
They commonly have white marks on their underparts with short necks and lengthy, slender hooked bills. Their wings are narrow and long with the male’s wingspan measures up to 7.5 feet from the taper to the points.
Their wings are made up of 11 primary feathers for flight, and the tenth feather is the longest while the eleventh isn’t fully developed. They also have 23 secondary feathers for flight. They have deeply forked tails, but it isn’t conspicuous unless the tail is fanned.
Their wings and tails form an apparent “W” shape during flight. Their faces and legs are fully covered with feathers, and their feet are weak and short.
The frigatebirds’ bones are very light in weight, and they only make up just 5% of their total body weight. They have a strong pectoral girdle with well-built pectoral muscles.
These muscles and the feathers equally make up about 50% of the total body weight. The males have a red-coloured throat pouch that is inflatable.
This pouch is also called a gular pouch, and the males use it to attract the females during the breeding season. The gular sac or pouch happens to be the frigatebird’s most distinctive feature.
Their preferred habitats are tropical and subtropical regions.
They mainly feed on small fish such as the flying fish, chased to the surface by predators such as tuna and dolphins.
They also feed on cephalopods, particularly squid. Frigatebirds also prey directly on eggs and the offsprings of other seabirds such as boobies, petrels, shearwaters and terns, in particular the sooty tern.
In contrast to other seabirds, frigatebirds drink fresh water when they approach it, by swooping down and gulping it with their bills.
The frigates have the largest ratio of wing area to body weight when compared to any bird. They spend most of their time in the air. Due to the build of their wings, they can soar for long periods, only flapping their wings on occasion.
A great frigate was once monitored by a satellite in the Indian Ocean, soaring for about two months. In freezing conditions, they can fly at heights above 4,000 metres.
They can spend the entire night on the air, taking their nap, but they always return to an island when they want to breed and roost.
During their hunt or foraging for food, a frigate can stay on the air for about 12 days. They are highly skilled in using their forked tails to navigate their flight and make powerful, deep beats with their wings.
Frigatebirds prefer to soar because they are not suited to flight by sustainable wing flapping. These birds bathe by flying low and hitting the water surface before they scratch and preen later. They are terrible swimmers, and they cannot perform flight from the sea with ease.
Even though these birds have a dark plumage in a tropical climate, they have figured out ways not to overheat. They use this, especially when they are exposed to full sunlight on the nest.
They shake their feathers to lift them away from the skin to boost air circulation. They also expand and upturn their wings to leave the hot undersurface exposed to the air. This triggers loss of heat by evaporation and convection.
Frigates typically mate on remote, oceanic islands and they usually breed in colonies numbering up to 5,000 birds. These colonies have a nesting group between 10 – 30 birds with rare cases of these groups numbering up to 100.
Mating can occur at any time of the year, but it mostly occurs during the availability of abundant food or dry season.
Frigates are known to have the most dazzling displays among seabirds. They exhibit this display to female frigates flying overhead by pointing their bill upwards, inflating their gular sacs and vibrating their extended wings. They create a drumming sound by vibrating their bills together and emitting a whistling call.
The female frigate descends from flight to meet with the male of her choice and lets him take her bill in his. The mating pair engages in shaking heads together.
After mating, the male usually gathers the sticks and the female makes the loosely woven nest. The nest is eventually cemented or covered with guano.
These birds prefer nesting in trees or bushes around, but they opt for grounds when vegetation isn’t available. They lay just a single egg that could weigh up to about 7% of the mother’s body weight. Both parents take turns in incubating the egg for a period ranging between 41 and 55 days.
The frigate chicks are naked when hatched, and they develop a white down. They are always protected by the parents for the first six weeks and feed on the nest for about six months.
Both the father and mother take turns to provide for the first three months, then the father holds back, leaving the mother to continue the chore.
The chicks feed from their parents by putting their heads in their parents’ throat and feeding on the partly regurgitated food. Unlike other animals, even birds, it takes the frigates a usually long period to rear a chick.
Frigates typically breed every year.
Aside from the declining numbers of two species of the frigates: the great and lesser frigatebird, the other three species of frigates are classified as “Least Concern”.