Thursday, October 09, 2014

Rise from your grave!

Well hello there. It's been a while hasn't it, but the Croc Blog has been on something of a hiatus lately. You can put this down squarely to its owner diverting his energies elsewhere, but this is all about to change... for the better.

First of all, there are not one, but two CrocLog Podcasts on their way. I know this because one of them has been recorded and is pretty much ready to go. Sadly it's a little bit out of date, but hey - let's call it a history lesson. The second hasn't been done yet, but we do have the interview recorded, so really it's nearly there.

Secondly, we'll have a guest blogger appearing soon. I won't say any more at this stage, in case it doesn't happen, but fingers crossed.

Thirdly, I'm back in Darwin again after several months of being here and there, so I'm sitting at a desk in the heat and humidity (the fan is on full) and writing reports, papers and other crocodile-related material. Some of this will surely make its way to the blog.

And finally, here's a picture of a crocodile, because I don't need an excuse!

Australian freshwater crocodile (Crocodylus johnstoni) on the Ord River



Tuesday, March 25, 2014

CrocLog Podcast - Episode 15

Brandon is currently in Belize helping out on a Morelet's crocodile research project, and we'll be recording a new podcast just as soon as he gets back. In the meantime, here is the long-lost Episode 15 of the podcast. This was recorded back in early December 2013, and for a variety of technical reasons was never quite finished. I've finally managed to get the laptop working that contained the audio editing software (humidity kills everything electronic up here), and you can finally listen to it below.

It's worth a listen because we have a good chat about human crocodile conflict as we discuss the launch of the CrocBITE database. We also end up talking about rattlesnake tails briefly, but soon get back onto the topic and hand by talking about tool use in crocodilians. Brandon discusses a few interesting crocodile attacks from last year, and we end up wondering where all the decent crocodile documentaries have gone lately.

Links to the podcast below:

Saturday, March 08, 2014

Crocodile predators, or crocodiles having a bad week?

Is that... a crocodile tail? Photo by Marvin Muller
Everyone is aflutter lately with some interesting photos doing the rounds that show crocodiles and alligators having what could be considered a bad day. First there was this great series of photos showing a water python (Liasis fuscus) subduing and eating a freshwater crocodile (Crocodylus johnstoni). The python was estimated to be around 10 feet (approx 3 m) long, and the crocodile between 3 and 6 feet (approx 1 to 2 m) long. It looks to me as though the crocodile was a little over 1 m in length. So it's still a juvenile crocodile, although it would still have been capable of killing the python had it gotten the chance. But pythons work most effectively when they surprise their prey and prevent them from retaliating. Wrappings its coils around the crocodile's body effectively restrained the limbs and the head, and prevented the crocodile from being able to do a thing. Crocodiles can certainly kill pythons easily, and I've seen the results of large pythons torn in two with a quick head flick by the crocodile, so this was a risky attack by the snake but the reward was an enormous meal that would last it for over a month.
The neck bite of doom for this alligator. Photo by Geoff Walsh
If that wasn't enough for the croc world, gators (Alligator mississippiensis) had to let the side down again, this time by being killed by an otter (Lontra canadensis). An otter, for shame! But let's not be too hasty. Just because mammals can be quite tasty doesn't mean they can't be deserving of respect. This otter certainly got the better of this alligator, having learned to bite it in exactly the right location to stay clear of those jaws while being able to tire it out. The article above describes alligators quite vividly as "a grenade" which is certainly apt. Like the snake tackling a freshwater crocodile above, the otter was taking quite a risk here. Alligator jaws are serious business, and getting the initial attack wrong could mean an incapacitating injury leading to death. But the otter knows exactly what it's doing, tiring the alligator out while it's frustratingly unable to deploy its explosive bite. Struggling alligators quickly run out of stamina, leaving the otter to snack on gator tail at its leisure while the alligator was still alive. The article above does make one error; the alligator doesn't die of lactic acidosis, that takes a few days assuming that its blood pH falls too low for its metabolism to correct it in time. The otter would have finished its meal long before that, the alligator having succumbed to its injuries due to blood loss.

While photos like this are fascinating to see because they reveal behaviour that we so rarely witness, they also give the false impression that it's rare for crocodiles and alligators to be eaten. This is a long way from the truth. Hatchlings serve as a tasty treat for a wide range of animals, including birds, large fish, large amphibians, large insects (even ant colonies), various reptiles, mammals and of course humans. That majestic 5 metre long saltwater crocodile basking on the bank without a care in the world? That animal had to endure a gauntlet of predators and other crocodiles for many years before it grew large enough to feel relatively safe. In a healthy population, less than 1% of the hatchling crocodiles and alligators that emerge from their eggs actually survive their first decade, and that's because the vast majority of them are eaten by predators. It's an r-selected survival strategy; invest in a lot of initially vulnerable offspring in the hope that a few of them make it to breeding age. It might seem cold-hearted to k-selected strategists such as ourselves, but you can't deny it works.

Eventually, these offspring reach a size where they're safe from just about anything except larger members of their own species. However, the two examples above show that there is no second prize for nearly making it.


Thursday, February 13, 2014

Can crocodiles really climb trees?


photo by M. van Welsem / Mabuwaya Foundation
Philppine crocodile adult
Vladimir Dinets, Matt Shirley and I recently published a paper entitled "Climbing behaviour in extant crocodilians". Here's a link if you'd like to read it. The resulting news stories have been quite extensive, to say the least! Everyone is fascinated by the idea that crocodiles, those vicious man-eating predators we keep hearing about, could climb trees. Perhaps it means that climbing a tree to escape a crocodile is no longer an option? Perhaps it means that crocodiles will start dropping from the branches onto your head for a surprise dinner date? Perhaps when you see a fallen tree by the river bank, you'll think "Wow, it must have been a heavy crocodile to bring that one down!"

Of course I'm just having a bit of fun. None of those possibilities are true, you'll be pleased to hear. Actually, it's been known for a long time that crocodilians (or crocodylians if you want to be pedantic) can climb out of the water onto floating logs and low branches. We didn't publish a paper to point this out, but rather we wanted to explore how widespread this was, and look into the reasons why crocodiles might do this, and even allow us to speculate on how extinct crocodyliforms may have behaved. After all, if you look at a modern crocodile and think there's no way it could climb a tree, you're not going to assume a fossil crocodyliform with a similar morphology is going to be able to do it either. Well, here's a cool thing, some modern species can climb trees, and they can do so remarkably well, often getting several metres off the ground up relatively steep trunks and branches. The modern crocodilian limb is more adaptable than you might have thought.

Tuesday, February 11, 2014

Accurate headlines: "Crocodile nightmare"

Crocodile drama (photographer unknown)
The media really loves crocodiles, not because journalists necessarly like crocodiles, but because the word "crocodile" casts a thrall over many readers. They see a headline with the magic word in it, and they have to click the link, or buy the paper in the newsagent. It's therefore too much to resist shoehorning the word "crocodile" into as many news stories as possible. Every so often when I see a really egregious example, in the interests of accuracy and balance, I'm going to write a more accurate version. I'll try and post these under the tag "Accurate headlines". So, let's get started.

Here's one (courtesy ninemsn) that struck me today, and it's a familiar theme. The headline is "Crocodile nightmare for four fishing mates". So wow, that sounds pretty dramatic! Were these four guys attacked by a crocodile? Perhaps they were threatened by one, or were in serious danger of being attacked?

Tuesday, December 03, 2013

Taking the bite out of crocodiles with CrocBITE

Crocodiles are neither evil nor malicious, but they do sometimes bite people. Photo Adam Britton
Today we (Big Gecko and Charles Darwin University) are launching CrocBITE, an ambitious project to archive all crocodilian attack incidents from around the world, the purpose of which is to improve our understand of human-crocodile conflict (HCC). HCC is arguably the biggest threat to crocodilian conservation now, a reversal of fortunes for those crocodilian species whose populations have recovered sufficiently to come into regular conflict with growing human populations. CrocBITE isn't about vilifying crocs; quite the opposite, it's about understanding risk factors, addressing conservation problems, improving human safety, and increasing respect (or at least tolerance) for crocodiles.

I wrote a piece for The Conversation which was published this morning, you can see that here. However, I thought I'd post the original version here. It doesn't contain half as much information, but it takes a slightly different approach and makes some valid points.

Monday, December 02, 2013

Can crocodiles use tools?

Smaug with hat, or devastatingly effective
camouflage? Photo by Brandon Sideleau.
A blog article over at Tetrapod Zoology (a site that you should bookmark and read regularly if you're not doing so already, because it's rather good) is running a story about tool use in crocodiles and alligators. Yes, that's right, tool use. We know that crocs are much smarter than people give them credit for, but are they really capable of using tools as well?

The article references a paper that's just been published digitally by Dinets et al (2013). They describe mugger crocodiles at the Madras Crocodile Bank appearing to balance sticks on their snout and sitting under nesting egret colonies. Egrets use sticks to build their nests, so they spot some floating in the water, land next to them, and get a nasty shock when they try and pick one up. The paper describes this as a deliberate attempt by the crocodiles to mislead the egrets into landing within striking range, with the sticks as the tools in the ruse. It's a compelling idea.

Seeing crocodiles with sticks, leaves and other vegetation balanced on their head isn't new, we've all seen them doing it. We have a large saltwater crocodile who lives in a pool covered with Fistia spp, an aquatic plant that makes a fetching hat when he surfaces underneath one. I suspect many of us have wondered whether this plays any kind of functional role, or whether it's simply the crocodile not caring either way whether it has plants on its head. I've seen crocodiles surface in such dense vegetation that they can't actually see, and shake their head to clear them off. Other times they seem to sit quite happily without apparently noticing. If you were a bird and saw a nice bit of vegetation and didn't recognise what was underneath it, you might think that crocodiles could learn to use this vegetation to increase their chances of catching prey. It's certainly feasible, but proving it is another matter entirely.

The Dinets et al. study suggests that mugger crocodiles only balance sticks on their head and sit under egret colonies during egret breeding season. This certainly supports the idea that something deliberate is going on, although it's still possible that it's incidental; perhaps the crocodiles spend more time sitting under egret colonies during egret breeding season, and those that have sticks on their heads might get lucky when an egret gets fooled? To counter this, the authors point out that the area around the egret colony doesn't have many sticks, suggesting that the crocodiles must bring them across to the colony for them to use as bait. Even if it is purely coincidental at first, crocs learn fast, and this might reinforce behaviour that makes sitting under a nesting egret colony with sticks on your head more likely.

I think it's a great observation, even though there's still a skeptical part of my brain wondering whether there might be another explanation. I'd love to see more work done on this, because a study like this opens up a whole set of really interesting questions. Science! What is true, though, is that crocodiles do some amazing and unexpected things, and it wouldn't surprise me if they were this cunning. We know that they're capable of it.

Dinets, V., Brueggen, J.C. & Brueggen, J.D., 2013. Crocodilians use tools for hunting. Ethology Ecology and Evolution, in press. doi.org/10.1080/03949370.2013.858276