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Frigatebirds

Frigatebirds

Frigatebirds

Aerial attitude

Text and photographs by Ross Wanless

he size of an ; the grace patrol the flyways, picking off hapless of a ; the belligerence of a victims as they return for the night. Once skua; the speed of a ; the they have selected a victim, as many as agility of a flycatcher and the five to 10 will give chase. attitudeT of... well, a . These They pull on the victim’s tail feathers, amazing are the undisputed, if bite its legs, drag it by a wing-tip and even somewhat despotic kings of the world’s stick their bills down the other ’s gul- tropical oceans. let to grab fish. that choose to resist Frigatebirds are impressive creatures by can suffer lethal consequences, such as whatever yardstick one chooses to meas- broken wings or becoming completely ure them. They are highly specialised exhausted. Often the victim will regurgi- seabirds, completely in tune with their tate some of its crop contents, and the environment. So well adapted, in fact, frigatebirds will then dive and chase the that they have pared down to the abso- ill-gotten gains. But they must catch it lute minimum anything not essential to before it hits the water and sinks, for their mode of living. Those features that ironically frigatebirds, despite being sea- are essential they have souped up to the birds, have no waterproofing. If they land extremes that drag-racing enthusiasts in the sea, they drown. would appreciate. For a not to have waterproof Their fame is widespread, well deserved, feathers sounds absurd, but frigatebirds and comes for several reasons. Perhaps have achieved this. It is questionable the most obvious trait is their well-known whether or not the ancestors of frigate- habit of attacking other seabirds, which birds ever had waterproofing, but it seems they do ostensibly to get a free lunch. probable that they did. Somewhere along Basically, they are the biggest and mean- their evolutionary path they became so Opposite Frigatebirds live hard and est kids on the block: they pick on other proficient at catching food in mid-air that play hard, are powerful and aggressive birds, bullying and harassing them until they did away with their waterproofing. predators, yet so light and manoeuvrable they cough up lunch money. Seabirds It is a popular myth that frigatebirds are that they can pick a twig off the surface returning to roost generally have a full obligate klepto-parasites (in other words, of the ocean. crop of fish and frigatebirds are wont to that they derive a living from pirating 

36 frigatebirds africa – birds & birding 1 1 2 2 3 3 4 other seabirds’ food). This is probably just as important is to be skilled metres. But size is not everything: they half a frigatebird’s weight. Frigatebirds are 4 5 clearly not the case: if noth- at pilfering nesting material. Another of also have the lowest wingloading of any by far the biggest birds that can hover 5 6 ing else, simple mathematics the frigatebird’s extreme adaptations is bird. For birds the size of frigatebirds to without a headwind. They can also fly 6 7 tells us so. For example, on the reduction of its feet and legs to such a achieve that is truly astronomical engi- more slowly than just about any other 7 8 Aldabra Atoll in the Indian degree that they can only be used for neering. Wingloading is the ratio between bird without falling out of the sky. With a 8 9 Ocean there are approximate- perching (and then only just). The birds the weight of a bird and the surface area reasonable breeze, they can even achieve 9 10 ly 10 000 frigatebirds (the cannot walk on land and thus struggle to of its wings. Clearly, the heavier a bird is, take-off without flapping – they simply 10 11 second largest colony in the find material with which to construct the bigger the surface area needed to spread their wings and float away. 11 12 world), and a similar number their nests. Dispossessing other frigate- achieve lift. Small birds such as sunbirds Yet another feature that makes frigate- 12 13 of Red-footed . It is birds and boobies of their twigs, especially have very low wingloading ratios, and birds so adept at aerobatics is the shape of 13 14 inconceivable­ that the boo- in the air before the birds can access the consequently are highly manoeuvrable. their wings. Straight, level wings are good 14 15 bies could find enough food relative safety of a nest, is a very valuable Bigger birds, like ducks and geese, have surfaces for gliding; angular, curved wings 15 16 to support both themselves skill for breeding birds. Getting free fish is such high wingloading ratios that they are good for agility. are 16 17 and the frigatebirds. probably an added bonus during training often have to run on the water before tak- extreme examples in the straight-winged 17 18 Frigatebirds eat sessions. However, having watch­ed their ing off, and must flap really fast to stay in department, as they have little need for 18 19 and flying almost evening antics for many hours, I firmly- the air. There is a fairly neat trend in birds: tight cornering or rapid changes in direc- 19 20 exclusively, hawking them believe that frigatebirds simply have ‘atti- the bigger they are, the higher their win- tion. Most birds lie somewhere along the 20 21 out of the air or from just tude’, and that they enjoy beating up gloading. spectrum, with more bowed shapes occur- 21 22 below the water’s surface as smaller birds. One of the ways frigatebirds achieve ring in birds that need more twisting and 22 23 When a male frigatebird is not display- the flying fish flee predators So what is it that makes the frigatebirds their low wingloading is having hollow turning power. Predictably, frigatebirds 23 24 ing, his gular pouch is visible only as a from below, principally and dol- so good at overhauling other seabirds and (pneumatised) bones which, all told, con- have highly bowed wings, making them 24 25 relatively small flap of skin on his throat. phins. Chasing down birds is perfect looting their lunch? For a start, they have tribute less than five per cent to the birds’ look the part of a child’s depiction of sea- 25 26 practice for the a massive wingspan – a Greater Frigate­ weight. In fact, the feathers and flight birds in the distance – gently-sloping ‘M’s. 26 27 aerial manoeuvring needed to capture bird’s wings stretch to more than two muscles (arguably the two most critical Their wings are also more bent at the 27 28 the much less agile flying fish. But it is metres, ’s to 2.5 features for flight) combined account for wrist than other birds’, further improv-  28 29 29 30 30 31 31 32 32 33 islands throughout 33 34 Relatively speaking... tropical oceans. 34 35 rigatebirds have the remnants of webs Off Africa, both the Ascension and a few Magnificent frigatebirds 35 36 F joining all four toes on their somewhat occur off the west coast, whereas Greater and Lesser frigatebirds 36 37 atrophied feet. This single character has been occur off the east coast, with vagrants reaching the southern tip of 37 38 used to place them along with , cor- the continent. There have been claims of Christmas Frigatebirds from 38 39 morants, and boobies in the the Kenya coast, but these remain unsubstantiated. Given their great 39 40 . However, recent molecular powers of flight, vagrancy is fairly common. However, the correct iden­ 40 41 evidence strongly suggests that this classifica- tification of single, out-of-range birds requires careful observation. 41 42 tion is incorrect, and that frigatebirds are 42 43 more closely related to albatrosses, , 43 44 divers and . 44 45 Worldwide there are five of frigate- 45 46 birds in a single , Fregata: 46 47 F. aquila Breeds only 47 48 on Boatswainbird Island off , 48 49 central . : The atrophied feet, showing the vestiges of webbing 49 50 Vulnerable between the toes, are shown clearly in this female 50 51 F. andrewsi Breeds Greater Frigatebird. 51 52 only on , an Australian island 52 53 south-east of Sumatra. Conservation status: Frigatebirds are unusual among seabirds in being sexually dimor- 53 54 Critically Endangered phic, with males being mostly or entirely black, and females having 54 55 Magnificent Frigatebird F. magnificens varying amounts of white on the breast or belly. Differences between 55 56 Breeds on tropical islands off the Americas, the species are rather subtle, especially among adult males. Their 56 57 with a very small population, relict on the identification is further complicated by each species having a series of 57

58 peter ryan (3) Islands, off West Africa juvenile and immature plumages. Young birds typically have pale 58 59 Puff daddy... a Magnificent Frigatebird in breeding condition displays his Greater Frigatebird F. minor Breeds widely heads and breasts, and take several to acquire adult plumage. 59 60 inflated gular pouch. on islands throughout tropical oceans An immature Magnificent Frigatebird. PETER RYAN 60 61 F. ariel Breeds widely on 61 62 62

38 frigatebirds africa – birds & birding february/march 2002 frigatebirds 39 1 2 3 ing their agility. Added of skin on the throat, called a gular case of the Greater Frigatebird. Frigate­ 4 to this is a deeply pouch, that they use in a dramatic visual birds are monogamous, but probably 5 forked tail which display to attract a mate. When the bird find a new mate at each attempt. The 6 makes a highly effec- is in breeding condition, the gular pouch female lays a single, large, white egg, 7 tive rudder. This is one is bright crimson, and the male inflates it which is incubated for around three 8 of the longest non- to many times its original size. It looks months; chicks fledge after about six 9 ornamental tail feath- like a massive red balloon strapped to the months. Frigatebirds are unusual in hav- 10 ers in the bird world. throat: quite extravagant for seabirds, ing extremely protracted periods of post- 11 They are also the only which usually go in for rather demure fledging parental care, with young birds 12 species to have a fused colorations. Males which are ready to being fed by their parents for up to 18 13 pectoral girdle that mate will inflate the pouch, then droop months after leaving the nest. This is 14 allows their bodies to their wings over the nest, raise their presumed to be a result of the long learn- 15 cope with rapid, high- heads and produce a variety of often very ing period required to master their high- 16 speed turns. All in all, peculiar, howling calls. Prospecting ly-skilled aerial feeding techniques. A 17 frig­atebirds­ are deli- females are welcome, but rival males that single breeding attempt can take as long 18 cately tuned flying come too close are chased off. Fighting as two years from the start of nesting to 19 Immature frigatebirds typically show a ma­chines. They are among males for nests can get quite the young becoming independent. 20 pale head and breast. cap-able of sleep­ing on the wing over sea, intense, and not infrequently the inflated Breeding is colonial, and the resultant 21 flying vast distances, producing bursts of gular pouch is targeted by protagonists. mêlée of several thousand birds squab- 22 unbelievable speed and catching and Once his pouch is punctured, a male can- bling, fighting, displaying, mating and 23 relieving almost any other seabird of its not attract a mate and thus cannot breed raising young, is one of nature’s great 24 meal. again until it heals. biological spectacles. 25 Another well-known character of this Once a mate has been selected and a With their massive wings, frigatebirds 26 charismatic is the male’s breeding nest secured, an elaborate courtship fol- can soar effortlessly for hours on end. 27 display. Male frigatebirds have a large flap lows; this can last up to two weeks in the The tradewinds of the tropics generate 28 thermals, rather unusually in that they 29 are over the ocean. Frigatebirds have 30 learned to ride the thermals to incredible 31 heights, gliding so high that one needs 32 binoculars and a steady hand to see 33 them. This allows them to travel vast 34 distances away from their roosting sites. 35 In this respect they are much like African 36 vultures; another similarity is the speed 37 with which they descend to a point 38 where food is, seemingly conjuring them- 39 selves out of thin air. Frigatebirds are very 40 gregarious, and besides communal roost- 41 ing and breeding, will often commute, 42 hunt and feed in large groups. 43 Despite being so atypical in many cies – namely Christmas and Ascension Top Frigatebirds of all ages crowd 44 respects, frigatebirds have one critical frigatebirds – give the most cause for con- a communal breeding tree on 45 aspect in common with the vast majority cern. The Christmas Frigatebird is restrict- Aldabra Island. 46 of seabirds: their naïveté. Seabirds typi- ed to a single colony which may be 47 cally breed on islands, usually remote severely impacted by an introduced ant Above Cute as it seems as a chick, this 48 and inaccessible, and away from preda- that is likely to kill nestlings as well as frigatebird will soon develop the bully-boy 49 tors. This has led, over aeons, to them cause other ecological changes on the habits of its elders. 50 losing fear of predators, including island; Ascension Frigatebird is threat- 51 humans. Some frigatebirds remain dis- ened by cats which have extirpated it 52 armingly ‘tame’ and approachable, such from the main island and could wipe out 53 as those on the Galapagos. This trust in the species if they make it across to 54 people has been their undoing at many Boatswainbird Island. 55 colonies, where humans have pillaged Frigatebirds epitomise the freedom and 56 them to local extinction. Frigatebirds wild abandon of the open oceans. They 57 have undergone some breeding-range live hard and play hard, are powerful, 58 contraction as a result of colonies being aggressive, even reckless predators, yet 59 deserted. With one exception, they now are so light and fragile they can pick a 60 breed only on protected or very isolated floating twig off the crest of a wave, or 61 Frigatebirds are highly gregarious and will hunt, roost and breed in large groups. islands. The highly range-restricted spe- drown at the merest miscalculation.  62

40 frigatebirds africa – birds & birding february/march 2002 frigatebirds 41

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