The Black caiman is the biggest of all species of alligator, some reaching six meters long. This impressive aquatic predator is the largest animal in the Amazon Basin. Superficially it looks like the American alligator, and its protective armored skin, as its name suggests, is dark in color. This skin color helps to camouflage it during its nocturnal hunts, and may also help to absorb heat. The lower jaw has bands of grey (brown in older animals) with white or pale yellow bands across their flanks. The banding fades gradually as the animal gets older.
These aquatic reptiles inhabit much of the area of the Amazon Basin, including much of both northern and central South America (Bolivia; Brazil; Colombia; Ecuador; French Guiana; Guyana; Peru). They occur in shallow, freshwater bodies of water like slow-moving streams, rivers, and lakes, and sometimes flooded savannah and wetlands.
From May until July there is a period of flooding throughout the Amazon, and at this time Black caiman are dispersed throughout their range. From September through December is the dry season, when water levels recede, savannahs which were flooded dry up, and these alligators are more densely gathered in the permanent rivers and lakes. They usually hunt during the night, using their sensitive sight and hearing to catch birds, fish, turtles, capybaras and some larger mammals. They have teeth that are made to grasp their food, but not chew or kill it, so they normally drown their catch, and, if it is of a small enough size, swallow it whole. They leave larger prey to rot, and, when decayed enough, they eat it. Black caimans make noises like rumbling thunder for communication with their own species. Like most crocodilians, they look after their young.
Black caimans are carnivores. Fish are the major part of this animal’s diet, especially catfish and the dangerous piranha, but adults also go after much larger prey like capybara, turtles, deer, cats and dogs. Juveniles eat smaller foods, including crustaceans, snails and other invertebrates, and fish.
Little is known about the mating system of Black caiman. Generally, crocodilians exhibit polygynous behavior, when males mate with more than one female during the breeding season. It is thought that female Black caimans nest from September to December, during the dry season, when water levels drop and fish have only shallow pools to swim in, providing an easy and abundant meal. These animals use plant material to build a nest mound measuring around 1.5 meters across, where a large clutch of as many as 65 eggs are laid. Females remain close to their nests, waiting 42 to 90 days for the eggs to begin to hatch, and they open the nest to help with the hatching process. Often many females next close together, so large numbers of hatchlings emerge at the same time at the start of the wet season, thus gaining safety in numbers. A mother will try to care for her young for a few months but they are largely independent. Most do not make it to adulthood. A female Black caiman breeds only once in 2 to 3 years.
For many years, this species was hunted heavily for its tough skin, to make shiny, black leather. Over the last century, this extreme hunting pressure reduced the overall population by 99 per cent, and it is now almost extinct in some places, such as Colombia, as well as the Amazon River itself. Populations continue to be impacted by illegal hunting, as well as habitat destruction through deforestation swamplands being burnt. Competition with the more common spectacled caiman may also threaten Black caiman populations.
According to the Animal Corner resource, the total population size of the Black caiman is around 25,000-50,000 individuals. According to the Crocodilian resource, the total population size of this species is up to 1,000,000 individuals. Overall, currently Black caimans are classified as Least Concern (LC) on the IUCN Red List.
Being the largest predator in the Amazon ecosystem, the Black caiman may play the role of a keystone species and help to maintain the structure of its ecosystem. Important activities may include nutrient cycling and the selective predation of certain fish species.