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1 .Last week, we started looking at reptiles, including crocodiles and snakes.
2 .Today, I'd like us to have a look at another reptile - the lizard
3 .- and in particular, at some studies that have been done on a particular type of lizard whose Latin name is tiliqua rugosa.
4 .This is commonly known as the sleepy lizard,
5 .because it's quite slow in its movements and spends quite a lot of its time dozing under rocks or lying in the sun.
1 .I'll start with a general description.
2 .Sleepy lizards live in Western and South Australia, where they're quite common.
3 .Unlike European lizards, which are mostly small, green and fast-moving,
4 .sleepy lizards are brown,
5 .but what's particularly distinctive about them is the colour of their tongue,
6 .which is dark blue,
7 .in contrast with the lining of their mouth which is bright pink.
8 .And they're much bigger than most European lizards.
9 .They have quite a varied diet, including insects and even small animals,
10 .but they mostly eat plants of varying kinds.
1 .Even though they're quite large and powerful,
2 .with strong jaws that can crush beetles and snail shells,
3 .they still have quite a few predators.
4 .Large birds like cassowaries were one of the main ones in the past,
5 .but nowadays they're more likely to be caught and killed by snakes.
6 .Actually, another threat to their survival isn't a predator at all,
7 .but is man-made - quite a large number of sleepy lizards are killed by cars when they're trying to cross highways.
1 .One study carried out by Michael Freake at Flinders University investigated the methods of navigation of these lizards.
2 .Though they move slowly,
3 .they can travel quite long distances.
4 .And he found that even if they were taken some distance away from their home territory,
5 .they could usually find their way back home as Iong as they could see the sky
6 .- they didn't need any other landmarks on the ground.
1 .Observations of these lizards in the wild have also revealed that their mating habits are quite unusual.
2 .Unlike most animals, it seems that they're relatively monogamous,
3 .returning to the same partner year after year.
4 .And the male and female also stay together for a long time, both before and after the birth of their young.
1 .It's quite interesting to think about the possible reasons for this.
2 .It could be that it's to do with protecting their young
3 .- you'd expect them to have a much better chance of survival if they have both parents around.
4 .But in fact observers have noted that once the babies have hatched out of their eggs,
5 .they have hardly any contact with their parents.
6 .So, there's not really any evidence to support that idea.
1 .Another suggestion's based on the observation that male lizards in monogamous relationships tend to be bigger and stronger than other males.
2 .So maybe the male lizards stay around so they can give the female lizards protection from other males.
3 .But again, we're not really sure.
1 .Finally, I'd like to mention another study that involved collecting data by tracking the lizards.
2 .I was actually involved in this myself.
3 .So we caught some lizards in the wild and we developed a tiny GPS system that would allow us to track them,
4 .and we fixed this onto their tails.
5 .Then we set the lizards free again,
6 .and we were able to track them for twelve days and gather data,
7 .not just about their location,
8 .but even about how many steps they took during this period.
1 .One surprising thing we discovered from this is that there were far fewer meetings between lizards than we expected
2 .- it seems that they were actually trying to avoid one another.
3 .So why would that be?
4 .Well, again we have no clear evidence,
5 .but one hypothesis is that male lizards can cause quite serious injuries to one another,
6 .so maybe this avoidance is a way of preventing this
7 .-of self-preservation, if you like.
8 .But we need to collect a lot more data before we can be sure of any of this.