The Black caiman (Melanosuchus niger) is a large crocodilian and, along with the American alligator, is one of the largest extant members of the family Alligatoridae and order Crocodilia. The Black caiman is the largest predator in the Amazon ecosystem, potentially capable of taking any animal within its range, including other predators. As the largest predator in the ecosystem, it may also be a keystone species, playing an important role in maintaining the structure of the ecosystem. The Black caiman is a dangerous species to humans, and attacks have occurred in the past.
The Black caiman has dark-colored, scaly skin. The skin coloration helps with camouflage during its nocturnal hunts, but may also help absorb heat (see thermoregulation). The lower jaw has grey banding (brown in older animals), and pale yellow or white bands are present across the flanks of the body, although these are much more prominent in juveniles. This banding fades only gradually as the animal matures. The bony ridge extending from above the eyes down the snout, as seen in other caimans, is present. The eyes are large, as befits its largely nocturnal activity, and brown in color.
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 in flooded savannah and wetlands.
From May until July, there is a period of flooding throughout the Amazon, and at this time Black caimans are dispersed throughout their range. From September through December is the dry season, when water levels recede, savannahs that 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.
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 capybaras, 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 the 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. Female Black caimans breed 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 percent, 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 and swamplands being burnt. Competition with the more common spectacled caiman may also threaten Black caiman populations.
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.