The Enigma of the Echidna
Scientists are continually perplexed by this egg-laying Australian mammal’s unpredictable behavior and strange physical characteristics
- Doug Stewart
- Apr 01, 2003
ONE OF THE MOST REMARKABLE SIGHTS that biologist Peggy Rismiller has seen in her years exploring the Australian bush is that of an echidna sunbathing. The short-beaked echidna, or spiny anteater, ordinarily resembles a spiky ball, like some kind of terrestrial sea urchin. To warm up on a cool morning, however, it will stretch out on the ground, its body as flat as roadkill, and lift its spines to let in sunlight. "It's amazing to see," Rismiller says. "It looks like a rug with spines."
On a continent teeming with weird mammals, the echidna is one of the weirdest. It has a beak like a bird, spines like a hedgehog, eggs like a reptile, the pouch of a marsupial and the life span of an elephant. Elusive and unpredictable, echidnas continue to perplex the scientific world with their oddities. Though normally wary of humans, a number of them reversed course and invaded the suburban streets and yards of Canberra in the fall of 1967—why, no one knows. "They're such an independent, enigmatic animal," says Rismiller. "Every time you think you know what they're going to do, they do something different."
Photo: © MIKE MCKELVEY
POUCHED EGG: Along with the platypus, the echidna is the world's only living monotreme, an order of egg-laying mammals found only in Australasia. After mating, an adult female lays a single egg about the size of a U.S. dime or an Australian five-cent coin directly into her pouch. The newborn puggle that hatches about ten days later stays in the pouch for several weeks to suckle. Eventually, as it reaches maturity, it will grow to about the size of a human infant. "They're so difficult to study," says researcher Peggy Rismiller, examining a puggle (above). "They're hard to find, they're solitary, they make no noise and they travel great distances."
Along with the platypus, the echidna is the world's only living monotreme, an order of egg-laying mammals found solely in Australasia. (The term comes from these mammals' single opening for excretion and reproduction, more like birds or reptiles than other mammals.) Monotremes branched off from the mammalian family tree some 120 million years ago and are the oldest of the 26 surviving mammalian orders. "Echidna" commonly refers to the short-beaked echidna, which is found across Australia. A second genus, the long-beaked echidna, lives in Papua New Guinea.
The first detailed description of the echidna was published in England in 1792. A decade later, another account included a meticulous drawing by Captain William Bligh, who had feasted on roast echidna years earlier during a post-mutiny stopover in Australia. Bligh had the foresight to sketch the strange animal before eating it. Not until 1884 did the scientific world learn to its amazement that both platypuses and echidnas laid eggs.
Since then, Australians have adopted the short-beaked echidna as a national mascot of sorts. It's among the most widely, if sparsely, distributed of all Australian mammals—wandering and burrowing its way across rain forest, desert, bush, swamp and seashore. The echidna's total numbers are unknown. "You can't do the usual mammalian trapping surveys because you can't trap them," says Rismiller. "Even food won't lure them." Concerned that their future welfare is not assured, Australia has officially listed them as a protected species.
In her 15 years of living in a pristine area for wildlife not far from Adelaide, Rismiller has become the world's foremost authority on the short-beaked echidna. Rismiller and her partner, biologist Mike McKelvey, work at the rustic Pelican Lagoon Research and Wildlife Centre on South Australia's remote Kangaroo Island. The two American expatriates, who are both now Australian citizens, operate the facility as a nonprofit educational trust that specializes in low-impact field research. It's the sort of place where computers are solar-powered and rain provides drinking water. Volunteers sweep bat guano from the tables each morning.
Rismiller works only with live, free-ranging animals, which is a challenge as echidnas are hard to find and harder to catch. When she arrived, she and her colleagues searched for 300 hours before encountering their first one. Small, dark, wary and virtually silent, an echidna in plain sight can resemble a low, nondescript bush. Rismiller now sees to it that a quarter of the four dozen echidnas roaming the Pelican Lagoon area of Kangaroo Island carry radio transmitters epoxied to a spine on their backs. (Traditional radio collars won't fit, echidnas being essentially neckless.) Still, tracking even radio-tagged echidnas isn't easy. "They're built low to the ground," says McKelvey, "and they spend a lot of time in burrows and caves, which block the signal." Moreover, a single spine can be a precarious attachment point. Says Rismiller, "I call one of the echidnas here our $10,000 male because he's shed so many transmitters." He may have learned to scrape them off between rocks.
Rismiller, who also studies tiger snakes, admits she's obsessed with echidnas. "They're such wonderful, attractive, enigmatic animals. They have a rolling, waddling gait. Their spines make them look formidable, but they're really quite gentle animals. To see their little beaks and their little eyes looking up at you, it's Lord of the Rings all over. You think: 'Here is a wise little gnome.'"
Adult echidnas are roughly the size and weight of newborn humans, but helpless they're not. Their short legs, heavy, backward-pointing rear claws, and broad shoulders are well-suited to powerful digging. Alone among mammals, echidnas can dig straight down, disappearing in minutes. Natural escape artists, echidnas can also dig through wooden garage doors and heavy plastic storage bins. Metal walls are a better deterrent, but they're not unbreachable, as researchers at the University of Melbourne discovered recently. A group of captive echidnas there were confined to a pen with corrugated-iron walls. "After three days," Rismiller says, "the researchers found the drinking bowls had been stacked in a corner, and all the echidnas had climbed out."
While hatchlings have an egg tooth for breaking out of the shell, adults are utterly toothless. They use their hard, skin-covered beaks, an extension of the skull, to root around vegetation, plow through soil and pry up rocks in a search for ants, termites, worms, grubs and other food. The short-beaked echidna's scientific name, Tachyglossus aculeatus, is apt: fast-tongued and spiny. The animal slurps up prey with a long sticky tongue that darts in and out of its beak.
Aussies may refer to echidnas casually as "porkies," but their spines have little in common with a porcupine's quills. Echidna spines lack barbs and are never thrown from the body. What's more, a porcupine can't use its quills to climb a rock crevice or right itself when upended, as an echidna can. "Echidna spines are actually modified hairs," says Rismiller. "They have a long root that goes into a special muscle layer no other mammal has." The animals can thus move spines individually or in small groups—to protect their heads, for example. "When you pick one up, the spines on its head will stand up straight while those on its back will lay flat." This muscle control isn't always voluntary. "During courtship, a male will stroke the spines on a female, and you'll see her spines undulating. It's very sensuous really."
Rismiller suspects that spines may aid in the species' survival in an unexpected way. Like other mammals, echidnas are hairy and milk-bearing, but their blood is only lukewarm. An active echidna's innards usually range between 88 and 91.5 degrees F, or 31 to 33 C. (An inactive echidna can be much cooler; to conserve energy, it can go into torpor, letting its body drop to as low as a few degrees above freezing.) "Cold doesn't deter them," says Rismiller, "but if their body temperature rises above 33 Celsius [well below what's normal for humans] heat stress will kill them." Echidnas have no sweat pores, nor do they pant. Might their spines, so deeply embedded in well-vascularized tissue, be capable of dissipating excess heat? The idea for now is conjecture, but Rismiller hopes to pursue it.
Much about echidna behavior is a mystery. "It's because they're so difficult to study," she says. "They're hard to find, they're solitary, they make no noise and they travel great distances." Their wanderlust is one reason they're ill-suited to captivity. Attempts to relocate them inevitably fail; even after a 30-kilometer drive, says McKelvey, "the animal is back almost before the humans are." Echidnas have no routines. They're active day or night, regardless of weather. They lack permanent dens, choosing instead to sleep in whatever burrow or cave is handy. They don't socialize and they haven't been known to fight. They forage in a home territory as large as 250 acres yet don't defend it. They tend to ignore any creatures they encounter, except when the time comes to mate.
During the Australian winter, as many as a dozen males form slow-moving mating trains, shuffling silently along in a lethargic parade led by a pheromone-emitting female. Trains can persist for more than a month, with males dropping out and rejoining, according to Rismiller, who first observed this behavior in detail. A receptive female may end up clinging to a tree trunk with her forelimbs while the males dig a circular trench around the tree as deep as ten inches. (Like crop circles, these tree trenches had mystified Australians for years.) The males then compete for mating honors.
"There's no aggression at all," says Rismiller. "The males just push each other around, head to head. As each one is pushed away, it leaves. It's quite incredible to watch." After this process of elimination, the winner lies on his side in the trench partway underneath the female, and they mate—slowly and, as is said of porcupines, carefully. If the female isn't game, she rolls into a defensive ball, and that's that.
After a three-week gestation, the female lays a single soft leathery egg about the size of an American dime. Rismiller discovered that the female does this while curled into a sitting position and lays the egg directly into her pouch. This shallow, temporary pocket is formed by a swelling of the mammary glands and the action of the stomach muscles. The baby echidna, or puggle, hatches in ten and a half days and remains in the pouch to suckle.
Like a newborn kangaroo, the puggle is essentially a mobile embryo: Its extremities are transparent, its eyes and backbone unformed, its forepaws capable of grasping but its hind legs mere buds. In two weeks, the hatchling gains 100 times its birth weight, growing from a third of a gram to about 30 grams. At seven or eight weeks, when the puggle starts to grow spines, the mother evicts it from her pouch (understandably) and places it in a nursery burrow. Thereafter, she visits for feedings every five or six days. In about seven months, the juvenile has a full complement of spines and claws and is foraging on its own.
Thanks to its armored exterior, an adult echidna has few native predators. On Kangaroo Island it has none, though a large monitor lizard called Rosenberg's goanna preys on spineless burrow young. Introduced predators are a bigger threat. Feral cats attack burrowing young as well as torpid adults. On the mainland, predators include dogs, feral pigs, foxes and dingoes. The echidnas' customary defense is to roll into a ball. Foxes and dingoes reportedly flip them onto their backs, urinate on them to make them uncurl, then pounce. Outside conservation areas, habitat loss and fast-moving vehicles are perhaps the species' gravest threat, however. (An echidna spine can puncture a tire, but it's always after the animal has died.) According to Echidna Watch, an Australian monitoring group, one in five echidna sightings is of a roadkill.
Those animals that evade mishaps compensate for their low-speed, slow-breeding life-style by often living 50 years or more. A Kangaroo Island local told Rismiller he had been watching the same full-grown echidna wander about his farm since he was a boy 45 years earlier. When she asked how he could be sure it was the same animal, he replied, "Easy. It only has three legs."
A final oddity about these very odd creatures: The echidna's neocortex, associated with reasoning and personality in humans, accounts for nearly half its brain's volume, compared to about 30 percent in so-called higher mammals. "What are they doing with it, that's the question," says Rismiller. "I think they're using it to play tricks on me, that's what I think. They use it to get rid of their transmitters."
Massachusetts journalist Doug Stewart's profile of bird-guide author David Sibley also appears in this issue.