As warmer weather sweeps across Australia it's not only human's feeling the heat. It's also impacting crocodiles in far North Queensland and their ability to hunt and survive.
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00:00Hi, Joe. So we've been tracking a population of saltwater crocodiles or estuarine crocodiles
00:08that live on the Wenlock River up in Cape York, and we've been recording their body
00:13temperature for the last 15 years to see how it's been changing. And what we found is that
00:19as the air has gotten warmer in the last 15 years, the crocs have become warmer as well.
00:26And so what's actually happening to their body temperature? Can you give us numbers?
00:30I can give you numbers, yes. It's going up by a fraction of a degree each year. So on
00:36average, we've seen that body temperature increase by about 0.1 degrees in the 15 years,
00:42which sounds like a small number, but it really does add up over time. And then the higher
00:47body temperatures that the crocs experience have been as much as half a degree higher
00:52now than they were at the beginning of this study back in 2008.
00:57And have you determined if that has more to do with the air temperature or water temperature
01:01or it's a mix of the both?
01:03So crocs are largely aquatic, and because they're cold-blooded, that means their body
01:08temperature is going to be impacted by their local environment. So by and large, this would
01:15be water temperature. But we've also seen these really interesting periods of time when
01:20the crocs become warmer or cooler than we expect, and we think that's where air temperature
01:26is coming into things. So for example, on a summer night, the air gets cooler than the
01:32water does, and we see these drops in temperature that we believe are the crocs' nocturnal basking
01:38to help them keep cool.
01:39Yeah, and that leads into my next question. What have you noticed about the effects on
01:44their behaviour from this?
01:47Yeah, so as the crocs' body temperature starts to exceed about 32 or 33 degrees, we notice
01:54that they are tending to cool rather than warm, which makes sense. But they also tend
02:01to have shorter dive length at these temperatures. The amount of time they can stay underwater
02:06becomes a bit more limited.
02:09And so when you say, when it gets to a certain temperature, that they cool rather than warm,
02:13how do they cool?
02:15Because we're tracking these body temperatures remotely, we don't have eyes on the crocs
02:20when we see this cooling happen. But there are some behaviours that we know crocodiles
02:24can use. Nocturnal basking is one of these, because water tends to hold on to the heat
02:30of the day much more than air does, and the air can become cooler at night or in the early
02:36morning. Another option is they may sit in the shade in cool runoff from springs, or
02:41if it's available, they may dive down to deep, cool pockets of water.
02:46And Caitlin, just a minor issue that I'd like to clarify with you, how do you track and
02:51monitor crocs?
02:53Sure. It's definitely easier said than done, because they do live in such a remote area
02:59and they can travel very far. So we use two technologies mainly to do this. One is satellite
03:06trackers, which are attached externally to the back of the croc's neck, and that picks
03:10up where they go and also when they're underwater. The other kind of technology is acoustic trackers,
03:17which are internally placed just below the arm, and that also picks up the body temperature
03:22of the crocs. And those tags can last up to 10 years, so we get some really incredible
03:27data from them.
03:29And Caitlin, have you been involved in attaching these satellite trackers?
03:35Yes, I've had the absolute privilege to go on a croc trip, which happens every August.
03:41I've gone on that a few times, and that's part of what we at the University of Queensland
03:47do while we're there. The main goal of it is to continue to track these crocs year-to-year.
03:52And can you tell us how you do that? Are the crocs caught in traps and then sedated and
03:57then you attach them, or how do you actually do it?
04:01Yes, so we do this work in collaboration with Australia Zoo, who are legends at croc catching.
04:08We let them do that part of the equation for us. They get the croc restrained, and then
04:15the science people come in, we attach the trackers, and we can also take measurements,
04:20see how the crocs are growing, and do some health checks.
04:23And what's it like for you to get up there in that country and be up close with these
04:28creatures that you're studying?
04:30I'm a city girl, so it is amazing to me. I really, really, it's an incredible experience
04:36being there. And because so much of my job involves looking at data, being able to actually
04:42get up close and personal with these animals that I study is such an awe-inspiring experience.
04:48Were you kind of freaked out on your first couple of experiences and then got used to
04:52it, or you were always kind of so intrigued by the science of it that you were cool, calm,
04:57and collected?
04:58I wouldn't say freaked out is the right word. There's definitely something quite incredible.
05:05The first time you see a crocodile in the wild, I had a moment of, wow, they really
05:10get that big? But over a few years, it's become something that is always incredible, but much
05:18more normal, if that makes sense.
05:21And are you concerned for their future, taking into account what you've found out about this warming?
05:28Crocs are really well adapted to the hot tropical environments where they live. And we do see
05:34that even when things get hot, they have these cooling behaviours that they can use. But
05:39even with all that, we have seen crocs approaching these thermal limits of 32, 33, 34 degrees,
05:47where we might end up seeing impacts of this into the future as the climate warms.
05:52And what's the next steps in your studies?
05:55The next step here is to see how these really hot periods are impacting the health of the
06:01crocs so that we can know what toll it might be taking, if any, on their condition.