Sunday, October 5, 2014

Giraffe — Nature's Tallest Yet Least Known Animal

Giraffes are the “forgotten megafauna,” said the  executive director of the Giraffe Conservation Foundation.

Our Understanding of Giraffes Does Not Measure Up

For the tallest animals on earth, giraffes can be awfully easy to overlook. Their ochered flagstone fur and arboreal proportions blend in seamlessly with the acacia trees on which they tirelessly forage, and they’re as quiet as trees, too: no whinnies, growls, trumpets or howls. “Giraffes are basically mute,” said Kerryn Carter, a zoologist at the University of Queensland in Australia. “A snort is the only sound I’ve heard.”

Yet watch giraffes make their stately cortege across the open landscape and their grandeur is operatic, every dip and weave and pendulum swing an aria embodied.

To giraffe researchers, the paradox of this keystone African herbivore goes beyond questions of its camouflaging coat. Giraffes may be popular, they said — a staple of zoos, corporate logos and the plush toy industry — but until recently almost nobody studied giraffes in the field.

“When I first became interested in giraffes in 2008 and started looking through the scientific literature, I was really surprised to see how little had been done,” said Megan Strauss, who studies evolution and behavior at the University of Minnesota. “It was amazing that something as well known as the giraffe could be so little studied.”

The species is not listed as endangered, but in the past 15 years, the population
has plummeted some 40 percent, to less than 80,000 from 140,000.

The species is not listed as endangered, but in the past 15 years, the population has plummeted some 40 percent, to less than 80,000 from 140,000. Credit Julian Fennessy
Giraffes are the “forgotten megafauna,” said Julian Fennessy, a giraffe researcher and the executive director of the Giraffe Conservation Foundation. “You hear all about elephants, Jane Goodall and her chimpanzees, Dian Fossey and her mountain gorillas, but there’s been a massive paucity of information about giraffes.”

Now all that is changing fast, as a growing cadre of researchers seek to understand the spectacular biology and surprisingly complex behavior of what Dr. Fennessy calls a “gentle giant and the world’s most graceful animal.” Scientists have lately discovered that giraffes are not the social dullards or indifferent parents they were reputed to be, but instead have much in common with another charismatic mega-herbivore, the famously gregarious elephant.

Female giraffes, for example, have been found to form close friendships with one another that can last for years, while mother giraffes have displayed signs of persistent grief after losing their calves to lions.

“Giraffes have been underestimated, even thought of as a bit stupid,” said Zoe Muller, a wildlife biologist at the University of Warwick in England. But through advances in satellite and aerial tracking technology, improved hormonal tests and DNA fingerprinting methods to extract maximum data from giraffe scat, saliva and hair, and a more statistically rigorous approach to analyzing giraffe interactions, she said, “we’ve been able to map out their social structure and relationships in a much more sophisticated way; there’s a lot more going on than we appreciated.”

For their part, male giraffes ever in search of the next mating opportunity have been found to be astute appraisers of the local competition and will adjust their sexual strategy accordingly. Males generally gain in rank and access to fertile females with age, and the alpha bulls flaunt that seniority physically and behaviorally: The twin ossicones that sprout like a snail’s tentacles on top of a giraffe’s head thicken and lose their charming tuftiness; a bony mass bulges up in the middle of the forehead; the neck musculature grows visible; and the male’s posture becomes ever prouder and more unflinchingly vertical.

Andre Ganswindt of the University of Pretoria in South Africa and his colleagues have found that young bulls recently launched on their rutting career will, when they’re on their own, mimic the basic demeanor of their elders: head held high, neck puffed out, females pursued and prodded and their urine sniffed for signs of estrus. But should a dominant bull saunter into view, the younger males instantly drop their sexual antics and seek to make themselves look small and innocent.

“It’s a case of ‘When I’m alone I’m the big giraffe,’ ” Dr. Ganswindt said. “But as soon as there are bigger bulls present, ‘No, no, no, I’m just a child.’ ”

The younger bulls have reason to fear their elders’ wrath. Dominance clashes between male giraffes can be terrifying spectacles, as each bull repeatedly “necks” the other, using his massive neck as a sling to slam his head against his rival, sometimes to devastating, even lethal effect.

Dr. Ganswindt saw one bull that had somehow survived with a broken neck. “The neck grew together again,” he said, “but at a funny angle.”

Giraffes are found throughout sub-Saharan Africa, currently classified as a single species with up to nine subspecies that differ by features like head shape and whether the fur on their legs is plain or patterned. The species is not listed as endangered, but researchers point with alarm to evidence that in the past 15 years, the giraffe population has plummeted some 40 percent, to less than 80,000 from 140,000.

Partly to highlight the crisis, conservationists this year declared June 21 the first World Giraffe Day — the longest day for the tallest animal, they said.

Researchers also emphasize the ecological importance of giraffes. “As large browsers, they’re habitat changers,” Dr. Fennessy said. “They spend a hell of a lot of time feeding, pruning, distributing seeds across the landscape, keeping the habitat open for other wildlife to use.” By going from tree to tree and blossom to blossom, he added, they even serve as pollinators.

A giraffe’s extraordinary mouth is like a set of human hands, its thick, prehensile lips and 18-inch-long, prehensile tongue can together grasp a leafy branch and then deftly pluck away the leaves while avoiding intervening thorns and barbs. Each day, and often well into the night, a giraffe consumes about 75 pounds of leaves, shoots, vines and occasional bits of dried meat licked from bones, all digested in its four-chambered ruminant stomach.

Giraffes also have excellent vision. Their eyes are among the largest of terrestrial mammals’, they can see in color and over great distances frontally, and their peripheral vision is so wide-angled they can essentially see behind themselves as well. Their keen eyesight lets them scan for predators, especially lions, which are their biggest threat apart from humans, and to keep track of each other.

Dr. Carter, of Queensland, and her colleagues followed more than 400 giraffes for six years, identifying their home ranges and who associated with whom. As the researchers reported in the journal Animal Behaviour, the females displayed clear and persistent social preferences. Some giraffes with overlapping home territories would never be found together, while others were sighted associating a good 80 percent of the time.

Continue reading the main storyContinue reading the main storyContinue reading the main story
Female giraffes can live 20 years or more, Dr. Carter said, and it makes sense they might rely on each other for clues to the best feeding grounds, help with calf caretaking “or to reduce stress, just by having somebody nearby.”

Thriving Under Pressure

Or perhaps to console each other. Giraffe calves are extremely vulnerable to predators, and though mothers will fight valiantly to keep their young alive — kicking their powerful legs forward and backward, sometimes delivering blows that can break a lion’s jaw — half or more of all calves are killed in their first year of life.

Echoing similar sightings by others, Dr. Strauss, the Minnesota researcher, described one case in which a mother spent four days lingering at the place where a lion had seized her calf, forgoing food and often in the company of two other adult females. “We’re just at the beginnings of trying to understand this kind of behavior,” she said.

Also of interest is the giraffe’s exceptional cardiovascular system. A large giraffe can stand 20 feet tall — the height of a second-story window — with its neck accounting for roughly a third its span and its long legs the same. The multitiered challenge, then, is how to both pump blood very high and retrieve it from far below while avoiding burst capillaries in the brain or blood pooling around the hooves.

 Giraffe is the tallest living terrestrial animal and the largest
ruminant — mammals w/ 
four-compartment stomach. 
As part of the Danish Cardiovascular Giraffe Research Program, scores of scientists have traveled to South Africa to study giraffe physiology. They have measured blood pressure at different sites and found readings that range from high to ridiculous — up to five times human blood pressure — yet with none of the organ damage commonly seen in hypertensive patients.

Instead, the giraffe has extremely thick blood vessel walls to prevent blood from leaking into surrounding tissue, while rugged, inflexible collagen fibers in its neck and legs help keep the blood traffic moving, rather as the tight antigravity suits worn by astronauts and fighter pilots will maintain blood flow under the most extreme gravitational shifts. A complex mesh of capillaries and valves store and release blood in the neck, allowing the giraffe to bend over for a drink of water and then raise its head again quickly without fainting; when the giraffe is standing still, sphincters at the top of the legs limit circulation to the lower extremities, to minimize the risk of fluid buildup around the hooves.

Researchers were also surprised to find that contrary to old textbook wisdom, giraffes do not have unusually large hearts for animals their size. “It’s half a percent of body mass, and that’s the same as we see in a cow, dog or mouse,” said Christian Aalkjaer of the department of biomedicine at Aarhus University in Denmark.

Moreover, Dr. Aalkjaer and his colleagues have determined that the giraffe’s cardiac output — the amount of blood pumped into circulation each minute — is modest, proportionally lower than it is in humans. That finding could help explain why giraffes rarely run for very long: Their hearts can’t deliver oxygen to their muscles fast enough to power extended aerobic exertion.

Or maybe the giraffes are worried about tripping over their own feet. Heather More and Shawn O’Connor of Simon Fraser University in British Columbia and their colleagues measured so-called sensorimotor responsiveness in the giraffe: how long it takes a nerve signal to travel from a muscle in the ankle up to the brain and back again. Reporting in the Journal of Experimental Biology, the researchers found that the nerve conduction rate in the giraffe is pretty much the same as it is in a shrew, rat or any other mammal.

Given the comparatively greater distance a nerve signal has to travel in the giraffe, Dr. More said, it’s possible the giraffe faces real challenges in reacting quickly to events down under — a rock beneath its hoof, or a bite to its ankle.

Evolution is always a trade-off, but for the giraffe the feeding advantages that came with elongation clearly outweighed any diminution in reflex speed. No need to run when you can be a quiet poem masked by a tree. — Natalie Angier | The New York Times

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