Frigate Bird

Frigate bird is also known as man-o-war bird that comprises five species that belongs to the family of sea birds scientifically known as Fregatidae of the order Suliformes and Genus Fregata. All the five species of this bird are classified under one genus and are widespread throughout the tropical and subtropical oceans. There are five main species of Frigate bird namely magnificent frigatebird, great frigatebird, Ascension Frigatebird, Christmas Frigatebird, Lesser frigatebird. All the species of frigate have a predominantly plumage of black colouration, long and deeply forked tails and a bill that resembles a long-hooked shape. The female frigate has a white underpart and belly whereas the male frigate bird has a gular fold that is distinctively red coloured and they inflate it to attract the females during the breeding season. 

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Because of their ability to fly through the wind currents for weeks, they spend most of their daytime hunting down the prey for feeding and roost at night on some cliff top or trees. They mainly prey on squids and fishes but are often caught by big predators like tuna when they arrive near the water surface to fetch their prey. They usually build a clumsy nest on the ground on a remote island or on the lower surface of the tree where they lay one egg in each breeding season and they are capable of breeding only once every year. 

They are also considered kleptoparasites as they are known to steal foods of other sea birds and snatch away the chicks of other sea birds. They prefer to stay in groups and forms colonies but are monogamous seasonally. The sister group of the Fregidae family is Suloidae that includes seabirds like cormorants, darters, gannets and boobies. Out of the five species of the frigate bird, two are endangered, which are, the Christmas and the Ascension frigate as their breeding habitat is just restricted to small islands for each individually.  Whereas the other three names, the great frigate, the magnificent and the lesser frigate are widespread throughout the world. According to the oldest fossils that aged more than 50 million years now, belongs to the era of early Eocene classified the three species in another genus named Limofregata that is believed to have shorter, less hooked beaks, longer legs and lived around freshwater areas.

Physical Description of Frigate Bird

The slender birds are usually larger in size, slender and are covered with black plumage and all the five species are similar in their appearances to one another. The magnificent frigatebird is the longest that measures around 114 cm in length and the other three species have the almost same length and are near the length of the former species. The lesser frigate bird possesses a body length that measures around 71 cms and is thus considered the smallest of all the five species of the frigate bird. The frigate birds are sexually dimorphic and the females are larger and about 25% heavier than the males. The females usually have white colouration on their belly which is lacking in the male counterpart.

Frigate birds have long slender hooked bills but short necks. They have long narrow wings that have the largest mass to body weight ratio as compared to any other bird. They are tapered at the points and the male frigate bird wingspan stretches up to 2.3 meters which is almost 7 feet in length than tappers at the points. There are eleven flight feathers of the birds that are primary with ten longest feathers and the eleventh one is a vestigial feather and is the shortest. Then they have 23 secondary feathers. They also possess a fork-like tail but it is not clearly and prominently visible unless they fan their tail feathers. Their legs as well as the face is completely covered with feathers. Their fully-web like feet are short and weak. Thus the webbing reduces and the toe of each part is free.

The frigate birds have air spaces within the bone and are thus marked as pneumatic with the making that is very light and comprises only 5% of the total body weight. As the bones are fused that makes their shoulder girdle very strong. Half of the bodyweight of the frigate birds are made up of their feathers and the rest half of the weight is equally made up of the muscles of feathers. The red gular pouch on the male’s throat is the most striking nature of the bird species. The pouch deflates slowly so that the males that are being disturbed can fly off with the pouches that are swollen for some time. 

They remain in the air for most of the time of the day and settle very little on the surface of the water. Therefore they tend to release very lees oil from their preen gland which is also known as a uropygial gland that releases very little oil so that whenever the bird comes in contact with the water surface its wings get saturated with seawater. But because of this phenomenon and the bigger wings with more weight than their body, they find it extremely difficult to take off quickly.      

Frigate Bird: Habitat and Diet

They are the species of tropical oceans and often prefers to ride in the warm small-scaling currents of air in the cloud under puffy cotton-like clouds that are also referred to as cumulus clouds. They often descend to the surface of the water for food such as flying fish along with the trade winds that supports them by facilitating the flying due to the windy conditions. They are widespread along the temperate regions but are not found in the polar regions. Adults are sedentary in nature as they are often found on the island for breeding. But the males are often noticed to migrate longer distances once they are completed with the process of breeding with one female colony. One of the male great frigatebirds was seen migrated from the islands of Europe in the Mozambique channel to 4400 km to the Maldives. Their genetic studies have established that they have an affinity for the same hatching site despite them being highly mobile birds. Though the yearlings that grow young displaces to farther places covering a wide distance up to 6000kms as on record. 

Feeding

The frigates are pelagic in their feeding behaviour and can fly up to 500 km from the land scavenging for food. They do not usually settle on the surface of the ocean water but snatches the prey from the surface of the water using their long hooked beak. They are usually known for preying on small flying fishes of the genera Exocoetus and Cypselurus that often swim to the surface in order to protect themselves from undersea predators such as tuna and dolphinfish. They also like to feed upon squids as well as other cephalopods that are found in the riffs. Frigate birds also use the techniques to follow the fish catching vessels from where they snatch away their prey as they are being fished and stirred in the vessels. Inversely, the fishermen tend to follow the bird to catch tuna as the frigate birds are known to have an association with the larger predators of the sea. Some of the frigates being the parasite also feed on the eggs and newborns of the smaller fish birds like boobies, terns, petrels, shearwaters and in particular the sooty terns. 

The species is expert in robbing other seabirds that primarily includes boobies and the red-footed boobies in particular with other tropical birds, shearwaters, terns, gulls, petrels including ospreys as well. They use their manoeuvring and speeding benefits to harass and outrun their victims constantly till they do not vomit out their stomach contents. The adult fridge either follow their targets after they have fetched the food or circles over the seabird colonies for the adults to come back with food-laden in their mouth to snatch it away. Although the frigate birds are known for their kleptomaniac nature that is not their primary process to obtain food and is just considered as a secondary option to collect food from hunting. By studying their robbing and snatching behaviour with the masked boobies, it is estimated that it can bring in up to 40% of its food requirement through the stealing practice but they have only seen collecting 5% of it through robbing.

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Ecology and Behaviour

As they have a large wing area as compared to the bodyweight proportion, they are often seen gliding in the air without flapping their wings much rather than roaming on the ground. They are primarily aerial birds and often prefers to drink water from freshwater resources by sucking it in through their long hooked bill as compared with the nature of other sea birds. A great frigatebird was once captured by the satellite above the Indian Ocean witnessed the frigate bird was up in the air for almost two months. They have a great flying ability of over 4000 meters even in freezing conditions.  Unlike swifts that are a high aerial bird of the family Apodidae that spends the night gliding in the air, they come back to their roosting site that can be a top of the cliff or in some trees situated on the nearby island. Field observation was carried out in the Mozambique Channel that has reported that frigate birds can stay up to 12 days in the air while they are scavenging for food. 

Their highly adapted forked tail is used for manoeuvring during their flights with strong deep wing beating that is otherwise not favourable for them to flap their wings often while flying. They usually bathe themselves by gliding down near the surface of the water and then splashing water on them followed by tidying, grooming and scratching themselves. The frigate birds do not know how to swim and they often find it difficult to take off quickly because of their heavy and large wings and short legs (that is not even Comfortable for them to walk). 

Many studies have found that the birds do sleep but uses only one hemisphere of their brain at a time and sleeps while gliding up in the air at higher altitudes. The amount of mid-air sleeping time that the birds acquire at night time is usually less than an hour. Though their average lifespan is unknown but among all the other sea-birds, the frigate birds are usually long-lived creatures. On the Tern Island of the Hawaiian Island, 35 ringed great frigatebirds were recovered in the year 2002. Out of the 10 great frigatebirds one was older than 37 years and another among them were older than 40 years. 

Even after having such dark black plumage non of the frigate species have been found troubled with overheating as they are mostly exposed to direct sunlight even when they are roosting in their nests. They usually pull up and spread their ruffle feathers to improve the air circulation of the body. They can even upturn their feathers on the most heated surface on their body to get ample air circulation for cooling it down. They usually put their head beneath tier winds for shade with a frequent fluttering of their gular sac.    

Distribution and Range of Frigate Birds

The Distribution and the Range of the Five Species of Frigate Bird are as Follows:

1. Magnificent Frigatebirds: they are found in the tropical Atlantic and breed in Florida, usually making their own colonies on the trees. They are also seen breeding in the Caribbean, and Cape Verde Island and also along the Pacific coasts of the United States starting from Mexico to Ecuador that includes the Galapagos Islands. 

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2. Ascension Frigatebird: mostly found in the Boatswain Birds Island just a little far from the Ascension Island that is situated in the Tropical Atlantic ocean but they have not bred in the Island since the 1800s.

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3. Christmas Frigatebirds: they are the breeding species that are only found on the Christmas Island that is situated in the Eastern Indian Ocean.

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4. Great Frigatebird: it ranges from Tropical Indian to Tropical Pacific oceans and is known to form colonies at Trindade and Martim Vaz that is in the south of the Atlantic ocean. In this ocean usually, the temperature of the water is warmer than 22 degrees celsius. They prefer islands or atolls that have sufficient vegetation as their breeding sites.

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5. Lesser Frigatebirds: they are found across Indian and Pacific oceans in the tropical and Subtropical waters. An Atlantic breed of lesser frigate bird named Trinities is only populated in the Trindae that is offshore to Eastern Brazil but is now extinct.

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Reproduction in Frigate Birds

They usually breed in colonies that comprise up to 50,000 birds and mostly prefer sites on the remote oceanic islands. Their breeding season lasts throughout the year but is prominent during the time of rich vegetation and dry seasons. These species have the most elaborate courtship session where the male takes up the female colonies in a large group that comprises up to 30 male frigatebirds. They take a sharp flight in the air with their bills pointing upwards and inflating their throat pouch. They also slightly vibrates their outstretched wings in order to display their lighter wings on the undersurface of the primary wing feathers.  They sometimes produce drumming noises or sometimes whistling calls by vibrating their wings. The females take a flight towards the male she has chosen for the mating process.

After copulation, the male gathers the sticks for the nest while the female builds the nest. They produce a single egg after a single mating that weighs 5-6% of the mother’s body weight. The incubation time is 41 to 55 days and both the parents incubates turn by turn. The hatchlings are born naked with the white down parts. They are cared for and protected continuously by their parents in the first 5-6 weeks and they are fed by the parents for the next 6 to 7 months. 

Thus the frigate birds are colonial in nature with large wings and have the longest period of parental care among all other bird families. They are klepto parasitic in nature where they fetch 5 % of their food from the other sea birds and usually hunt down the small fishes and squids by themselves as they flow to the surface of the water and catch them with their large hooked beaks. They are mostly aerial and tends to sleep at night while gliding up the higher altitudes and can soar for many days while scavenging. They roost on cliffs and trees and prefer temperate tropical and sub-tropical islands for breeding.