Friday, 28 February 2014

Kings of the New World (3): The Black Caiman

by Rob Cooper

Picture a set of black jaws emerging from the water as you stoop to drink; the consummate ease with which they move through the air belaying the sluggish appearance of the creature it belongs to as they close around your throat. Unfortunately this is far from the killing blow. The teeth of crocodilians are designed to grab and hold not to pierce or crush despite there being enough force to shatter bone. You are dragged into the waters of the amazon desperately flailing, held captive by a creature both far more at home and more powerful than you. Your dreaded captor then allows itself to sink dragging you along for the ride. The truth will soon emerge that crocodilians rarely actually kill their prey they simply immerse them in the lethal waterways they call home. The final of the great Amazonian predators is itself a living fossil. The black caiman is one of largest extant reptiles and is the largest predator in the amazon Basin. Akin to all modern crocodiles the black caiman shows little deviance from the genesis of the crocodilians over 200 million years ago. This giant reptile can. In some areas, routinely reach lengths of 4-5 metres and can reportedly reach 6 metres long and weigh over a tonne. 

In an earlier article I highlighted how the Jaguar often preys on the various caiman species in its environments. The black caiman however is the one exceptions. Whilst juvenile caiman are eaten by all manner of predators including snakes, storks and other caimans the adults have no natural enemies other than man and can be up to ten times the size of the Jaguar, putting them firmly off the menu.

As the caiman grow their diet shifts quiet remarkably. Young caimans eat crustaceans and insects than graduate to eating fish such as piranha and catfish and the adults often hunt large mammals that come to drink at the water’s edge such as Tapir, capybara, deer and jaguar. This is an example of different aged animals occupying different niches in order to reduce intraspecific competition (between members of the same species). The advantage of having less competition is that there is more food available to each individual because fewer organisms are taking a share so genes and behaviour promoting this system is perpetuated by natural selection.

Caiman also show a great deal of motherly attention. Mother caiman are well documented to help the hatchlings out of their eggs upon hearing their characteristic squeaking sound from within the egg. The young caiman upon hatching from the nest form a pod that is protected from predators by the presence of a large female. Pods can also contain individuals from other nests who became separated from their siblings. This behaviour has led to a great deal of speculation about the parental habits of dinosaurs as the brains of crocodilians share many features with that of therapod dinosaurs such as Allosaurus and Tyrannosaurus; many more similarities than when compared to birds, the other close relative of dinosaurs.

Unfortunately the black caiman recently nearly went the same way as the dinosaurs. Between 1950 and 1970 (when the species was classified as endangered) hunting decimated the populations in South America in order to collect its commercially valuable hide. Fortunately since then the black caiman populations have been increasing although conservation efforts face a problem when the creature in question is large and dangerous and according to the locals can regularly predate upon humans of all ages as well as dogs and livestock of any size. Normally people tend to be removed from the habitats of the black caiman but some groups such as the Rupununi River people live on the river itself in one of the last strongholds of the black caiman and live their lives fearing attacks from the deep and mourning loved ones lost to the primeval reptiles. Clearly such a struggle between man and beast is not easy to resolve.

The ancient giant Purussaurus
But what makes the black caiman stand out from contemporary crocodiles such as the American alligator or the Nile crocodile? Apart from being the largest member of the alligator family the black caiman in particular has a spectacularly large head even amongst crocodilians. A 3.9 metre long black caiman has a significantly longer skull than a 4.8 metre Nile crocodile. This adaption is thought to be geared towards the taking of larger prey items but there are few statistical studies due to low level of information regarding the black caiman. In addition most caiman species are characterised by large skull sizes without specifically taking large prey items, although other species could be limited by body size. The giant extinct caiman Purussaurus, which died out merely 8 million years ago, took this adaption to its zenith with a titanic 1.4 metre long skull on its 11-12 metre body. The black caiman is the closest organism we have today to such giants.

As I alluded to in the first paragraph the killing strategy of these caiman is something very reminiscent of a horror movie. The kill is not quick or clean; but it is very efficient. The teeth of all crocodilians, the caiman included are conical and sharp but not serrated. These teeth can trap small slippery prey such as fish to be swallowed hole and firmly keep hold of larger prey such as a tapir in order to drag it under water where the prey can be safely drowned without the predator having to grapple too closely with the prey species or evolve ways of killing them. All the caiman needs is its impressive skull and 1900 newton bite force to finish of almost any prey item equipping them to tackle all prey items in their environment including other caimans. 

What can we learn from the black caiman then? Firstly I think it is both thrilling and terrifying to consider the great rainforests of the world still harbour such impressive wildlife. Secondly that conservation isn’t always the simplest matter in the world. It would be lovely if we could protect all wildlife still remaining but the harrowing stories of natives eaten by black caiman remind us of a past time when man really was at the mercy of the bigger, more powerful animals around him. Finally the most positive message is that we can save animal species. One simple change in the law to prevent hunting of black caiman has saved the species from an untimely demise and that is a promising message for the future. For all his capacity to do wrong man also has the capacity to do good.