26 de noviembre de 2020

Do ostriches really hide their heads under the ground in times of crisis?

Most of us happily get by on a single cartoonish idea about ostriches: They’re the big birds that bury their heads in the sand in times of crisis, supposedly thinking that if they can’t see danger, danger can’t see them.

In our ragbag of stereotypes, ostriches have thus become the quintessential dim-witted animals. Even the Bible says they’re dumb, and bad parents too.

The head-in-sand idea is a threadbare, 2,000-year-old hand-me-down from the Roman naturalist Pliny, who sometimes passed on tall tales. Think about it. Ostriches have long, bony legs, a torso held aloft like a great floating raft of flesh and feathers, and a neck like a periscope, topped by a wedge-shaped head with eyes bigger than an elephant’s, at a height of up to nine feet. It is an unlikely design for head-burying.

Ostriches do in fact often hold their heads low to the ground—not under it—to feed on plants or to tend their nests. But their necks are light and flexible, with 17 cervical vertebrae to our seven, and easily move up and down, side to side, and front to back. And their giant eyes help them keep close watch on the world around them.

They have reason to stay alert. For starters, they’re basically oversize chickens in habitats populated by hungry lions, leopards, hyenas, African wild dogs, and cheetahs. And while adult ostriches are too formidable to be easy prey—their kick can break bones, and the larger of their two claws can disembowel an adversary—they’re much better at fleeing than fighting, with a top escape speed of more than 40 miles an hour.

What also keeps them alert is the peril facing their offspring. Ostriches make their nests—just clearings on the ground—in the open, where their eggs can be smashed to bits by any blundering elephant, never mind hungry predators. (Well, mind the predators too.) Success requires improbable luck.

The largest bird on Earth, and one of the most conspicuous, must keep its nest undetected—or stand ready to defend it—for more than two months, from laying the first eggs to hatching. Failure is routine, and that is the driving force behind its ingeniously communal nesting behavior.

A good place to see ostriches is Tarangire National Park in northern Tanzania. It’s 1,100 square miles of dry hills and grassy plains along the Tarangire River. The elephants spread out in great herds here, together with zebras and wildebeests by the thousands.

Ostriches are common too, but when I join University of Dar es Salaam wildlife ecologist Flora John Magige, an expert on ostrich behavior, on a search for nests, our first discovery is a bust.

Nine eggs are scattered in the brush over an area roughly 75 feet across. Magige surveys the area like a detective working a murder scene. She points out a faint scraping in the dirt where the nest had been, and right next to it the freshly dug burrow of an aardvark. Not guilty, she thinks. The scattering is more likely the work of a hungry predator, but not a big one, because all the eggs are still intact. Maybe a jackal then? In any case, the male and female ostrich have moved on, as they often do when a nest is disturbed. It’s possible that they’ll nest together again.

But ostriches in breeding season are relentlessly promiscuous, with both males and females seeking liaisons with multiple partners. No doubt they have their reasons. But from an evolutionary perspective, playing the field is a way to get diverse DNA into as many nests as possible and compensate for the fact that most nests fail.

Thus at 10:30 one morning we spot a couple mating about 500 yards off the park’s main road. They break apart, and as the male walks on, his most recent consort and two other females follow. One of them soon begins soliciting him, holding her wings away from her body and shaking them like pom-poms. In breeding season, females can produce an egg every two days, and the urge to make the egg fertile is insistent. But males are often in short supply, perhaps because they jealously guard their territory, forcing some to emigrate.

The male ignores her. Their walk takes them on a meandering route past tall, spreading acacia trees and squat baobabs with fat trunks scarred by the endless scraping of elephants. By the road, the female tries again, her wings shimmying. A safari vehicle shoots past, casting a train of dust across her romantic display. The male walks on. Undaunted, she finds an excuse to walk in front of him, wings low and trembling.

(Edited from National Geographgic  Magazine)

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