It was an item that needed to be handled with the utmost delicacy, but given the choice, would prefer not to be handled at all. Casey the echidna had already cost researchers thousands of dollars in lost tracking transmitters and here he was, minus his transmitter once again.

Still, he was a welcome sight. We'd been growing a bit despondent, feeling our chances of sighting one of these elusive mammals slipping away with the afternoon. Another echidna we had been stalking for nearly an hour through thick scrub had done a runner and disappeared under a skin-ripping spiky acacia.

But there, a couple of shrubs away, was Casey - digging into the soil and teasing his pursuers with the spine-free patch on his back where he had shed the last attempt to Araldite him to the world of electronic measurement.

Echidnas are among the world's most unusual animals and yet most Australians have little experience of them, except as the bristling ball that curls up in the middle of the road, only to be ruptured and splattered by car tyres.

It turns out that two of the foremost experts on the lives of these animals are originally American - Dr Peggy Rismiller, who is attached to the Department of Anatomy at Adelaide University, and her husband Mike McKelvey, a widely published wildlife photographer. They've spent more than 15 years on Kangaroo Island, off the South Australian coast, studying the life history, population ecology and biology of the echidna.

Despite their years of professional dedication, Peggy and Mike admit that the inroads they have made into understanding the life and times of the echidna are largely due to volunteers. Last weekend I joined eight of them to follow echidnas under the glaring limestone light of this spectacular island.

We were a diverse group. In an age in which folks are constantly told it is OK, indeed desirable, to pursue personal gain and pleasure, here were people prepared to devote their weekend and $550 - enough for a lazy, luxurious getaway somewhere - to scramble through scrubland to help the survival chances of animals that could hardly be called cuddly.

They had all come as part of a weekend discovery briefing organised through the Earthwatch Institute, an American-founded organisation that offers about 130 different volunteer programs worldwide. The choices range from environmental activities like this to assisting with archaeological digs and even aiding a public health program in India.

With me on this venture was a young Adelaide vet, a retired Melbourne teacher whose husband has Alzheimer's, an optometrist from San Francisco who wanted a break from working all day in the dark, a biology student from Wollongong, a Toyota dealer from Port Macquarie and an arts-law student from Canberra whose passion is Latin and philosophy.

Many of them were Earthwatch veterans, addicts even: the retired teacher had already done four activities, the car dealer three and the optometrist two.

Peggy's and Mike's association with the island began when Mike first visited in the late 1960s. In 1982 he bought the land that is now Pelican Lagoon Research Centre, which adjoins the larger Pelican Lagoon Conservation Park on the island's eastern end. Peggy, who had been studying reptiles as part of her PhD in Germany, came in 1988 to study the island's tiger snakes. The relationship with Mike blossomed in the glow of torchlight as the two took snake-blood samples at night.

Their interest in reptiles continues. As well as their echidna work, they continue to study Rosenberg's goanna, a metre-long lizard almost extinct on the mainland.

These are not the only creatures in their lives. A mob of dusky western grey kangaroos, led by a 14-year-old hand-reared female called Ruby, hang around the centre. They come up to strangers, sniffing and following like dogs.

More nervous are the Tammar wallabies, also almost extinct on the mainland, equally curious, but keen to keep a safe distance. On the bays around the lagoon, fairy penguins make their nests in the sand dunes and caves.

Because the island is rabbit-free, the vegetation understorey is intact and much thicker than similar mainland landscapes. Here, common brushtailed possums like to live on the ground, unlike tree-dwelling relatives elsewhere.

Visits to Pelican Lagoon are much in demand but strictly limited to no more than eight at a time. Peggy says this is because eight extra humans is considered the maximum carrying capacity of the land; in other words, the number who can walk across the fragile landscape, drink its water and dispose of bodily waste without doing environmental damage.

They are somewhat scathing about so called eco-tourism. "You have 40 people turning up to places in a four-wheel-drive bus," says Mike. "They scramble out across the landscape, before they get back in the bus and do it again in the next place. You can't say that is looking after the environment."

Here, visitors might arrive by car but then move around by foot only, walking 10 or more kilometres a day across boot-destroying rocky ground and clothes-ripping undergrowth.

Among them a few years ago was celebrity naturalist David Attenborough. He recorded a series of echidna sequences on the site, including one kneeling down where a female echidna kept trying to crawl under his crotch. "The out takes of that would be interesting," says Peggy.

Until the arrival of motor vehicles, echidnas had survived everything nature could throw at them for 120 million years, starting their evolution well into the age of dinosaurs, which ended 65 million years ago. But now Peggy fears the echidna may be in trouble. These creatures live up to 50 years and the surviving population is ageing. She is concerned that the next generation of echidnas might not have the numbers to replace deaths from cars, cats, foxes, electric fences and agricultural chemicals.

Australia's echidna (the short-beaked variety) is one of three survivors from the earliest order of mammals called monotremes. They are mammal-like, with warm blood, fur, and milk to feed young, but reproduce like reptiles with eggs. The other two survivors are our platypus and the endangered long-billed echidna of Papua New Guinea.

Despite their strange reproduction and their bodies being covered with spines that are actually modified hair follicles, the echidna has another enigma - a proportionately large brain. The front part of the neo-cortex, sometimes called the silent brain and believed to determine personality, takes up 50 per cent of an echidna's brain. In humans it is 30 per cent, and the only other animal to match the echidna is the dolphin.

Peggy says their tracking and behavioural studies have demolished the concept that the echidna is a primitive animal. "They have survival strategies we understand very little about, which have implications for the survival of all animals, including humans. One of the important things about echidnas is they never overpopulate an area. A lot of people don't like to hear it said, but that is something humans have never learnt."

At the end of the weekend, participants were full of praise, even the Earthwatch veteran, American optometrist Jennifer Ong, who had previously done work protecting threatened cactus in Mexico and leatherback turtles in Costa Rica. "This is easily the best one I have been on. The others all try to convince you their project is the most important thing on earth, but here you got a real sense of the practical global implications of what they were doing," she says.

"I come from a Filipino background, and for our culture the idea of volunteering is very strange. Relatives ask what I am being paid and they can't understand when I tell them I am paying. But I now find I have to do one of these every year. I want to give something back."

Her reward was lots of wildlife sightings, including the elusive goannas and the dolphins in the lagoon. We saw a Pacific gull tackle a sea eagle that had just lunched on a heron. There were lots of flowers and unusual plants, a nearby coastline gradually being eyed by developers, and for the strong of stomach, an autopsy on an echidna road kill.

But what about Casey? No one here has worked out how he gets rid of the $350 transmitters, except that some have been tracked to narrow limestone caves, where he might have discovered he can scrape them off.

Here he was again, the Araldite freshly set on the latest device. He was placed on the ground and without much fuss slowly walked off into the scrub, stopping occasionally to look at us over his shoulder. He'd get rid of this one too. We knew it. He knew it.

FAST FACTS

The next Kangaroo Island discovery weekend, in April, is already booked out, but more will be scheduled. For information on the Kangaroo Island program, or any of another 130 projects Earthwatch offers worldwide, including 17 in Australia, check : www.earthwatch.org. The Earthwatch Australia office is at 126 Bank Street, South Melbourne, 3205. Phone 9682 6828.

Getting there: Visitors can easily reach Kangaroo Island by sea or air. A 30 minute flight from Adelaide brings visitors to Kingscote Airport. Or take a coach from Adelaide to Cape Jervis, and the ferry to Penneshaw. For information: www.tourkangarooisland.com.au or phone (08) 8553 1185.