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