Sunday, June 28, 2020

The Great Pause Week 15: Pirata

ack in February, before the Pause began, I used to see and hear a half dozen incoming commercial airline flights during any of my daily ocean swims. They would pass directly over the island on approach to Cancun, many having been out over the Atlantic for most of the night. Then, in March, the skies fell silent.

Now, in their stead, the sound of my strokes are accompanied by the flap of wings. Herons, egrets, osprey on individual flight paths; formations of pelicans, cormorants, flamingos in line or V-formations, the pelicans taking advantage of ground effect air currents to buoy their weight, the flamingos hurling high overhead like javelins, and the cormorants somewhere in between, pumping wings to keep pace. And then, circling on thermals like scout planes and watching the entire scene, we have the frigate birds, “las piratas,” the ones the Maya called chimay. 

It did not take me very long, when I first observed them, to conclude they have better avionics than any flying creature or aircraft. I have previously written about the advantages of bats’ guidance systems, involving fine wing- and ear-hair antennae and echolocation that allow them to make steep turns, rolls, and flips at high speed in zero visibility, but they have nothing on the chimay when it comes to aerobatics.

You see, the Fregate magnificens is at a 50-million-year-old evolutionary disadvantage when it comes to getting food. Lacking gulls’ and vultures’ broad antibiotic resistance, it cannot consume carrion (although this makes them less prone to death by plastic). They cannot clear the slit nostrils on their bills of water if submerged, the way most fishing birds can. They do not have oil in their feathers to repel water. Hence, they must use their hooked nose to snag live prey, not even touching their bills to the sea. Their four-toed webbed feet prevent them from snaring fish the way ospreys and sea hawks can. There are only two means for chimay to eat: catch a fish or squid midair as it jumps or is thrown by another predator; or steal it from the grasp, nest or belly of a competitor. Hence the name, “pirate bird.”

Las piratas remain in the air and do not settle on the ocean. They produce very little oil from their uropygial glands so their feathers would become sodden if they settled on the surface. In addition, with their long wings relative to body size, they would have great difficulty taking off again.

It is not uncommon for me to see brief aerial combat between a gull and a chimay. The gull is fleeing with a small fish in its beak and a chimay takes up pursuit. The white gull can bank steeply, climb, dive, and even invert, but it lacks by a large margin the aeronautical tools its greenish black pursuer possesses. It has brought a fish to a dogfight. 

No matter which way the seagull banks, the chimay can turn inside that radius. It effortlessly executes a backward flip to cut off the gull’s reverse in direction, rolls over, and snatches the fish from the mouth of the outmatched bird. Checkmate black, in five moves.

Sometimes, pursuing a gull or a pelican, the chimay will use their superior speed and maneuverability to outrun and harass the other, pecking them in flight, until they regurgitate their stomach contents, which it will deftly scoop up in midair before it hits the ocean.

This is all the more astonishing when you consider that a chimay may have a wingspan of 2.3 meters (7.5 feet), the largest wing-area-to-body-weight ratio of any bird. Its wings can keep it aloft for weeks at a time when it is out on the open sea. Individual birds have been observed to range 6,000 km (3,700 mi) of open ocean. One great frigatebird, being tracked by satellite in the Indian Ocean, stayed aloft for two months, taking naps while it rose on updrafts. Since it cannot swim and can barely walk, the sky is home, apart from the short time it roosts in the low branches of mangroves, every second year, to produce a single chick. Here in the Yum Balam we might have 3000–5000 breeding pairs this year.

Fregatidae, so classed by Jean-Baptiste Du Tertre in 1667 from the French for la frégate, a fast warship, were called Man of War birds by the English. Columbus called them rabihorcado or “forktail.” Consider the design of this bird, drawing upon attributes found almost nowhere else. Its main wing is hinged in the middle, always bent, like a bat. Its broad, 22-feather wingspread and pneumatic bones let it hold its weight aloft on faint thermals, like a condor. Long feathers at the tip of each wing are given tiny muscles like fingers, letting them separate and point to change direction and pitch in an instant. The tail feathers are a second wing. When it is cruising, they are brought together the same way a flamingo reduces friction by forming a straight line to slice headwinds. When it is maneuvering, such as after spotting a school of fish about to leap, its tail feathers fork, twist at angles to each other, fan out to brake the bird’s forward momentum, and, in combination with its short neck and bent wings, twist to execute a power dive to that precise place where that school reaches the water’s surface, leaps into the air, and dives back to safety, now minus one of their members. 

According to a study in the journal Nature Communication, scientists attached an accelerometer and an electroencephalogram testing device on nine great frigatebirds to measure if they slept during flight. The study found the birds do sleep, but usually only using one hemisphere of the brain at a time and most often while ascending to higher altitudes. Each snatch of mid-air sleeping was less than an hour and always at night.

Mating pairs jointly build their nest, take turns sitting on the lone egg for 2 months, and feed and guard the chick for five to six months thereafter. It will take the chick a decade to reach breeding age and take its first mate, but once safe in the skies, it may live to its mid-40s. 

Between the big silver birds on noisy approach to Cancun and these silent masters of the wind, I will take the black bird every time.

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1 comment:

ElizabethAnn said...

Something interesting I learned about frigate birds in Belize is that blue-footed booby colonies are sometimes mixed with frigate bird colonies. The boobies do the fishing and the frigate birds steal from them. Why they nest together is a bit of a mystery but the theory is that the presence of frigate birds is protective in some way of the booby nests.




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