Unit Seven: Terence Dawson
Animal: Form and Function

Interview: Terence Dawson

Professor Terence Dawson is known throughout the world for his knowledge of kangaroos and other Australian animals. I first met Dr. Dawson when I visited the University of New South Wales in Sydney in 1993. He was explaining that one of the dangers of working on kangaroos at close range is that an animal might grab you by the collar with its forelegs, rear back on its tail, and then fire kicks with its powerful hindlegs at your midsection. "What," I asked him, "is the best way to react in such an emergency?" His advice: "Turn sideways!" I got the picture. The opportunity to learn more about Australian animals from Terry Dawson came in 1997, when I returned to Australia to conduct this interview.

What experiences fueled your interest in Australian animals?

Like so many who grow up in country towns, you just wander around, you fish and hunt. Whenever we were out of school we just wandered around the bush. This was savanna country in western New South Wales, and there were lots of birds and diverse habitats. Probably the first real interest I had in biology, as such, was the tradition of collecting bird eggs, which was one of those things country kids once did in the spring. I got much more interested in it than most of the chaps that I was collecting with, and I actually started to try to find out about the birds. One of the first books my parents gave me was What Bird Is That?: A Guide to the Birds of Australia. I got hooked on reading about the birds and trying to understand them. I knew then I wanted to study natural history and be a zoologist, but in those days, one had to have a profession. Being from a farming community (although my parents were not farmers), I decided after I graduated from high school to study agriculture. I went off to a small university, the University of New England, to start an animal science degree. I figured that studying domestic animals and animal science was a good way to operate close to natural history. But I made a decision to move out of agriculture if I got the chance. I got that chance with a postdoctoral fellowship with Knut Schmidt-Nielsen at Duke in North Carolina. I was still interested in large animals, and Schmidt-Nielsen worked on camels. I saw that I could utilize my training on sheep and cattle, which was directed to understanding how animals live in the environment, to understand the animals that I was much more interested in. So I ended up going in the direction of comparative physiology, or ecological physiology. I learned from Schmidt-Nielsen the notion of whole-animal biology—that you can't look at just one system if you're interested in how animals live in their environments.

When did you start to apply these ideas to Australian animals?

My interest in kangaroos developed in an odd way. When I was in the States, people used to ask me about kangaroos, but I really didn't know much about them. I went to the Duke library to find out about kangaroos so I could answer questions people kept asking me. There I realized that basically nothing scientific was known about kangaroos, so I decided that if I got the opportunity when I got back to Australia I would work on kangaroos. The other motivation stemmed from the idea at the time that kangaroos and other marsupials were primitive and inferior as mammals. That didn't fit very well with my childhood observations of kangaroos. I had seen them out in the open plains where the temperature was about 50° Celsius. Birds were even falling off their perches, but the kangaroos just sat there unperturbed, which didn't seem like primitive thermoregulation. Also, if a kangaroo got moving, hunting dogs couldn't catch it, and that didn't strike me as being inferior. So these notions that marsupials were generally inferior as mammals just didn't sit well. I thought, "Well, we'll go and have a look and see what the real situation is." I returned to Australia when the Zoology Department at the University of New South Wales in Sydney was developing a kangaroo research team and the university had just acquired a 100,000-acre field station in far western NSW. So I joined the Zoology Department here, and it's been too good to move. Our animals are just so fascinating that once you get involved with them, you're hooked. Marsupials and monotremes do things so differently. They break quite a lot of "rules."

But you want to be sure that we understand that "different" doesn't equal "primitive."

The moment you think about how these animals are living in their environments—how they feed, or the stresses they face—you can't possibly think of them as primitive. For example, we always wondered how the platypus, a monotreme, found its food. Platypuses dive and forage on the bottom of streams with their eyes and ears closed. One hypothesis was that platypuses use touch receptors in the bill to feed, but platypuses can locate and feed on guppies in the open water of a large fish tank, and so it's not only touch. They're actively hunting. As it turns out, platypuses also have electroreceptors. They can pick out the twitch of a fish muscle or a worm muscle and home in on their prey. In the 60 or 70 million years that platypuses have been around, there has been a lot of time for such special adaptations to evolve.

Much of your research has focused on marsupials, especially kangaroos. Tell us about some of the reproductive adaptations of kangaroos.

The group consisting of kangaroos and wallabies is actually a fairly modern group. The gray kangaroos go back about 7 million years, but the red kangaroo has a fossil history that goes back only about 100 to 150 thousand years. That is a very modern, recent animal in evolutionary terms. Gray kangaroos and red kangaroos have very different reproductive patterns. Gray kangaroos are seasonal breeders, while red kangaroos breed all the time, unless there is a drought. After a female red kangaroo mates and an egg is fertilized, the embryo doesn't implant in the uterus, but just stops at the 100-cell stage until about 30 days before the previous offspring is expelled from the pouch, and then it starts to develop again. The previous young doesn't just decide to get out; it's expelled when the female contracts the pouch and the young can't get back in. It's controlled by the same maternal hormone that functions in birth in eutherians. A day or so after the big young has been expelled, the next young is born, climbs up, and gets in the pouch. A day or so later the female mates again, and the whole system just keeps going. She's producing a young out of the pouch about every 8 or 9 months. You'd think we'd be up to our ears in kangaroos, but the mortality of young is high.

But during its time in the pouch, the young has good parental care, right?

At that stage, it's much better than human patterns. The kangaroo mother can pull the pouch open and have look inside and scratch its young. She also has to clean the pouch, of course. The young can get in and out. It's like you can have trial births. Once you're a wobbly young, you can get out and have a look around, and if you don't like it you can get straight back in and be carried by mom when she hops off.

Speaking of hopping, tell us more about kangaroos' unique locomotion.

Kangaroos are the only large animals that hop. Most of our work on locomotion is on red kangaroos. These behave differently from other kangaroo species. When they are disturbed, red kangaroos head away from the trees onto the open plain. Off they go, a magnificent flight, and nothing can catch them. Gray kangaroos head into the timber and use the trees as an escape mechanism, but red kangaroos rely entirely on speed. We really don't quite understand the hopping locomotion yet. The energy pattern is unusual. As most animals go faster, from walking to trotting to running, there is a roughly linear increase in energy cost. When moving slowly, kangaroos are rather clumsy, using their tails as fifth legs. But at 6 kilometers an hour (kph), they start to hop, and once they do that, the energy cost doesn't increase as they go faster, at least not up to the speeds we've been able to measure on treadmills. At 30 kph, the energy cost for the hopping is about half that of running for an animal of equivalent size. We initially thought it was related to elasticity in the legs, a bit like the energy saving you get when using a pogo stick. The spring stores the energy when you come down, and you can use that energy for takeoff. This the kangaroos do, and it is probably an important part of the system. But this is not unique to kangaroos; it's an important mechanism in any fast-running animal, including racehorses. There are a variety of other possibilities, but we really don't know the answer. What we need is a much bigger treadmill. You can fool a kangaroo into hopping on a treadmill, but when the length of the hop they would take in the open country becomes considerably longer than the length of the treadmill they start to balk. Their perception of where the end of the treadmill is gets them rather upset, and they start taking smaller steps, which upsets the normal hopping pattern. So we need a very long treadmill or perhaps a nice video in front of them to convince them that they are out there in the country. We're actually designing a bigger treadmill.

How fast can red kangaroos go on the open plain?

They can reach about 45 kph mainly by increasing stride length up to 5-6 meters per hop, and then they can increase to about 60 kph for a short distance by increasing the frequency of the hops. They can only sustain that speed for about 250 meters—to dash across the road in front of a car, for example.

What impact have humans had on the diversity of kangaroos and other marsupials?

The diversity of marsupials, especially large ones, was much greater when the aboriginal people arrived in Australia about 45,000 years ago than it is today. Big animals are easy to hunt, and virtually everywhere in the world where humans came into contact with animals that were naive with respect to humans, there was megafaunal extinction—disappearance of many species of large animals. The next major extinction in Australia occurred with the arrival of Europeans and the grazing industry. Much of Australia is not very fertile, and the climate is dry and erratic. The settlers had European notions of rapid growth rates for the vegetation, and they moved in huge flocks of sheep, and then with the first drought the ecosystem collapsed. The grazing also resulted in severe erosion. A major extinction of native animals occurred within the first 20 years of the arrival of European settlers to the region. The system just collapsed, and the aborigines were also decimated because most of their food was gone. That occurred even before the added problem of introduced feral animals such as cats and foxes, which prey on small marsupials and native rodents, and rabbits, which compete for food with native animals.

Do modern ranchers view kangaroos as pests that compete with sheep for food on the range?

That's changing, to some degree. Certainly when I was a lad, kangaroos were considered to be pests, and the opinion still holds among some graziers or pastoralists. But a lot of research shows that fluctuations in vegetation are due mainly to the erratic nature of our rainfall. Most of the time there's no competition between the kangaroos and the sheep because there is more vegetation than the animals can eat. And even in dry times in arid regions, the kangaroos feed mainly on grasses and don't eat a lot of bushes, which the sheep do eat. So, some of the pastoralists are now accepting that there's not much direct competition. They're also looking toward kangaroos as an extra source of income, both for food and for the tourist industry. People pay big money to come to Australia to see kangaroos. There is also less tension now because most conservationists are convinced that the six extant species of large kangaroos are not becoming extinct. Kangaroos are widespread and abundant. My best guess, based on aerial censuses, is that there are about 50 million kangaroos. We've got lots of kangaroos!

If some ranchers and conservationists are changing their view of kangaroos, is this part of a more general trend in Australian awareness about the native biota?

Yes. When I grew up, the attitude was: If it moves, shoot it; if it doesn't, chop it down. I think the current interest of Australians in the country's natural history is part of a general worldwide increase in awareness of the environment. But, particularly in Australia, we've become aware of the unique nature of our environment and our animals, and scientists have played a major role in uncovering a lot of the interesting things about our animals. Biologists are sharing these interesting things with the public, and as people acquire more knowledge, they become even more interested. Awareness of our unique fauna and understanding that our environment is particularly fragile is now much greater than I would have predicted just 10 years ago.

©2005 Pearson Education, Inc., publishing as Benjamin Cummings