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.

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