Almost every time I stop by a crocodile enclosure in a zoo, I hear people wondering if these are real animals or plastic models. Captive crocodilians (crocodiles, alligators and their less-known relatives such as caimans) don’t move that much. And this “laziness” has fooled people for centuries.
Virtually every popular or scientific description of crocodilians, from Herodotus two thousand years ago to school textbooks of the 1990s, calls crocodilians not just lazy, but stupid (even if more polite or scientific-sounding words are used). When I started my research on crocodilian behavior ten years ago (as a Ph.D. student at the University of Miami, upon a suggestion by my adviser Steven Green), I shared this misconception.
There were some dissenting voices. In 1935, E. A. McIlhenny described some really interesting behaviors; in the 1960s L. Garrick with colleagues discovered a complex signaling system used by crocodilians. But McIlhenny wasn’t a professional zoologist, so his accounts (known today to be entirely accurate) were distrusted by scientists, as were other unusual claims scattered in even older literature. And Garrick, content with discovering some cool things such as crocodilians using infrasound (acoustic vibrations too low for humans to hear), didn’t try to study the behavior of these animals more broadly.
I knew that crocodilians were the only large non-marine animals to survive the mass extinction that wiped out all non-avian dinosaurs. More than one crocodilian lineage managed to survive the catastrophe (the split between crocs and gators pre-dates it). I intuitively felt that there had to be something special about them. But I had no idea what it could be, and scientific literature of the time wasn’t much help.
We shouldn’t be too critical of scientists. Studying crocodilian behavior is a zoologist’s nightmare. Much of it can’t be seen in captivity, but observing it in the wild is difficult and sometimes dangerous (in the last ten years, three crocodilian researchers have died in the line of duty). Crocodilians inhabit murky waters, mosquito-infested swamps and impenetrable rainforests. They are mostly nocturnal, and many have become obsessively shy after decades of overhunting. They are specialized ambush predators, with numerous adaptations (such as the most sophisticated heart in the animal kingdom) allowing them to conserve energy, in part by not moving too much. For example, they don’t hunt very often: being cold-blooded, they eat about ten times less than mammals of the same size (their ancestors were warm-blooded and more active, but that was over a hundred million years ago). It’s not unusual to watch a crocodile all day and never see it move, so you need a lot of patience and endurance.
Crocs in the Night
So I became pretty much the first zoologist to systematically observe crocodilians in the wild at night. I began with a relatively easy species, the American alligator, and then studied over twenty others. And it worked. Within a week I began discovering new things, and this exhilarating marathon of discovery just never ended. In five years I got my Ph.D.; it took me four more years to follow up on some leads that were outside the scope of my thesis, and to publish everything (including a popular book Dragon Songs – check it out on Amazon). By that time the subject of crocodilian behavior was no longer a scientific swamp: researchers all over the world are now studying it and making one discovery after another.
So, what have we learned in the last ten years?
Crocodilians are not stupid. They have relatively small brains, but, just like in birds, these brains are organized very differently from mammalian brains: their volume is utilized more efficiently. These animals are smart and have very complex behavior, instinctive and learned.
They use a sophisticated, flexible communication system. It is a combination of sounds, infrasound, chemical and visual signals, produced by unusual and still poorly understood physical mechanisms. This system can be easily optimized to work in a broad variety of habitats, from overgrown marshes to flooded forests to large open lakes. Crocodilian “language” is so perfect that for the last 70 million years it hasn’t changed much: alligators and crocodiles still largely understand each other.
They are deadly hunters, second only to humans in versatility. Their hunting techniques are only partially known, but we have found that they can hunt as effectively on land as underwater, cooperate with each other (for example, chase prey into an ambush, or form a chain to drive schools of fish into shallows), and use lures. Alligators and crocodiles that live near egret rookeries often float with little sticks on their snouts during the birds’ nest-building season. If an egret looking for building material tries to pick up the stick, it promptly gets snatched. But they are not strictly predatory: they can eat fruit and even be important seed dispersers for some tree species.
They are surprisingly social, particularly gators. American alligators gather on spring nights to dance and then sing in choruses in the morning. They are promiscuous, but often have preferred partners and mate with them year after year. Crocodiles have a more hierarchical social system… but this aspect of crocodilian lives still needs a lot of research before we understand even the basics.
They can be excellent parents. In some species both mother and father protect and feed the brood; in others multiple females bring their babies together into a crèche and take turns watching over it.
And they can be playful, friendly, even funny. They play with toys, with each other, and with other animals such as otters. They can become tame and form strong bonds with people. One amateur naturalist in Costa Rica rescued a wounded crocodile, and the animal became his faithful friend: for many years the man and the huge crocodile played together and even pulled little practical jokes on each other.
But don’t try that at home. They might look like plastic models, but they can be very fast, and you can’t presume to be smarter than them.
This article was written by Vladimir Dinets, of the University of Tennessee, Knoxville. He has spent a decade studying the behavior of crocodiles, evaluating their habits and noting playful interactions and complex behaviors.