Birds
Magnificent Frigatebird
Fregata magnificens · also called magnificent frigatebird, man-o'-war bird, pirate bird
The magnificent frigatebird is a seabird that has almost entirely given up on the sea’s surface. It cannot land on the water without drowning, so it lives in the air — soaring for weeks at a time on enormous wings, snatching flying fish without getting wet, and bullying other seabirds out of their catch when the chance arises.
Overview
Magnificent frigatebirds live along tropical and subtropical coasts and islands of the Americas, plus the Cape Verde islands. They roost and nest on remote islands and spend the day on the wing over warm ocean, hunting flying fish and squid at the surface, stealing from other seabirds, and taking turtle hatchlings and seabird chicks near colonies.
Built for endless flight
The frigatebird has the lowest wing-loading of any bird — a 2.4-metre wingspan on a 1.5-kilogram body. Tracking shows individuals staying airborne for up to two months, climbing inside cumulus clouds to over 4,000 metres and gliding downwind for tens of kilometres between thermals. They snatch brief microsleeps in flight.
No water landings
Its feathers are not fully waterproof and its legs are tiny, so a frigatebird on the sea becomes waterlogged and cannot take off. It feeds, drinks, and bathes entirely on the wing or from a perch.
Piracy
The “man-o’-war bird” chases boobies and tropicbirds and forces them to drop or regurgitate their food, catching it in mid-air. But this kleptoparasitism is only a supplement — most of the frigatebird’s diet is its own surface-snatching.
The red balloon
In courtship, the male inflates a bare scarlet throat sac into a huge balloon over about 20 minutes, holding it for hours while drumming his bill and calling to females circling overhead.
Status
The magnificent frigatebird is Least Concern, numerous across its range, though colonies are vulnerable to disturbance and introduced predators.
Magnificent Frigatebird: common questions
Why can't a frigatebird land on the water?
Two reasons. Its feathers lack the dense waterproofing that ducks and other seabirds have, so they soak through quickly, and its legs and feet are tiny and weak, useless for paddling or for pushing off a water surface. A frigatebird that ends up sitting on the sea becomes waterlogged, cannot generate enough lift to take off again, and will usually die. Everything it does — catching flying fish, snatching squid, drinking rainwater, even bathing by dipping — is therefore done in flight or from a perch, never from the water. This is unusual and limiting for a seabird, and it is the reason frigatebirds have evolved such extreme flight efficiency.
How do frigatebirds stay in the air for weeks?
They have the largest wings relative to body weight of any bird, which means they can glide and soar with almost no energy expenditure. GPS tracking of frigatebirds has found individuals remaining airborne continuously for up to two months, covering thousands of kilometres. They climb inside cumulus clouds on rising air, sometimes to over 4,000 metres, then glide slowly downwind for tens of kilometres before finding the next thermal, in a roller-coaster pattern. They have also been recorded taking very short bursts of sleep — a few seconds at a time, sometimes with one half of the brain — while gliding, though they sleep far more when they can rest on a perch.
Do frigatebirds really steal food from other birds?
Yes, and it is where the "man-o'-war bird" and "pirate bird" names come from. A frigatebird will chase a returning booby, tropicbird, or gull, grab its tail or wing, and shake or harry it until the victim drops the fish it is carrying or vomits up its stomach contents, which the frigatebird then catches in mid-air. However, studies show this kleptoparasitism provides only a modest fraction of a frigatebird's diet — the majority still comes from its own surface-snatching of flying fish and squid. Piracy is a supplement that pays off when other birds are concentrated and vulnerable, such as near a colony.
What is the male's red balloon for?
It is a courtship display. The male magnificent frigatebird has a patch of bare, bright red skin on his throat, the gular sac, which he can inflate with air over about 20 minutes until it forms a huge, taut scarlet balloon under his bill. Groups of displaying males sit in the low bushes of a colony with their sacs inflated, wings spread and quivering, heads thrown back, clattering their bills and making a warbling, drumming call, all directed at females circling overhead. A female chooses a male, lands beside him, and the pair bonds. The sac is deflated and much less obvious outside the breeding season.