英语听力精选进阶版 8219（在线收听）

Now, have you ever wondered why koalas hug trees? And apparently, according to a new scientific study it is to stay cool. That discovery was made by researchers from the University of Melbourne who were looking at how koalas regulate their body temperature.

And one of my students Natalie Briscoe, her PHD was focused on this question in terms of the koala. And one of the questions we want to ask about the koala is, do they use behavior at all to regulate their temperature, are they able to choose places in their trees that make them a bit more comfortable.

And how did you go about finding this out?

Well, initially we went about this by putting a little weather station on a very long pole and lifting that weather station right up next to the koalas that we had radio transmitters on, and at the same time going around to other random places in their habitat and measuring the conditions in the trees of those locations. But what Natalie noticed was that the koalas in the hot weather would come down and will go to the thicker trunks. And they would flop onto those trunks and drop them limbs there. And we couldn't quite understand why they were doing that, but she also sought to measure the tree trunk temperatures and we found that they are actually quite a bit cool than the air. And then we took a special kind of camera that takes pictures of heat and tells us the temperature of every service in the picture. And it was so obvious once we got those pictures back. What the koalas were doing? They were putting their bottoms into the trees and dumping all their excess heating to the tree.

And were you surprised by what you found because it's known or presumably zoologists know that the fur on the stomach of the koalas is a lot thinner than it is elsewhere.

Yeah, well, we knew that and we thought, well, maybe they, I guess one idea was that they just expose that during the hot weather so that heat comes out their chests into the air. What we didn't realize was how much cooler the tree trunks were than the air temperature.

That wasn't obvious to us. It was obvious when we looked at the trees with the special camera, but it wasn't before that. And then it made a whole lot of sense. And it's really surprised a lot of biologists.

And it's always eucalyptus trees, is it?

No, it's not. And not all eucalyptus trees is good as each other for this purpose, so we measure a whole, a few different species of eucalypts in their habitat where we did the study and also another kind of tree called acacia. And it turned out that the acacia was actually the best one. But they don't eat the leaves of the acacia trees, they only eat the leaves of the eucalypt trees.