Melanosuchus nigerBlack caiman

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Geographic Range

Black caimans are found throughout much of the Amazon Basin; their range includes much of northern and central South America. Although these animals are far less common now than a few decades ago. (Britton, September 15, 1999; Thorbjarnarson, 1998; Thorbjarnarson, July/August 1999)

Habitat

Melanosuchus niger is often associated with steep banks alongside slow-moving freshwater rivers, lakes, wetlands, black water swamps, and seasonally flooded areas of the Amazon. (Britton 1999, Magnusson 1987).

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

The largest predator in the Amazon, Melanosuchus niger is capable of growing to more than 6 m. It resembles the American Alligator but is biologically more closely related to the other caimans. The Black Caiman retains its distinctive skin markings into adulthood: they display grey or brown banding on the lower jaw, and display white or yellowish bands on the sides of the body (Britton 1999, Magnusson 1998).

Reproduction

Good information concerning the Black Caiman's breeding habits is not plentiful. In the dry season, which runs from September through December, the female builds a nest mound, using the hind feet to dig an egg chamber. Clutch size averages 39.3 eggs, which are elliptical, with rigid shells, and average 143.6g. The female generally remains close to the nest site, although not all actively defend the nest. She will scrape open the nest when the hatchlings are emerging. The incubation period lasts between two to three months, but may vary with nest temperature. Nests may be warmed by sunlight or by the heat of decomposing vegetation. Hatching may correlate with the onset of the rainy season.

Hatchlings tend to congregate together in groups called pods. Pods may contain individuals from more than one nest, and they are often protected by the adult female's presence. -M. niger- pods were found to occur in areas of deeper water than -C. crocodilus-, implying choice of nesting sites in lower-lying areas (Britton 1999, Da Silveira et al 1997, Herron 1990, Thorbjarnarson 1998).

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)

Lifespan/Longevity

Behavior

Few good ecological studies have been made on the habits of M. niger. Despite having a range that overlaps with other species of caimans, M. niger appears to have its own ecological niche that enables it to coexist without too much competition.

May through July marks a period of flooding in the Amazon, and during this time the populations of Black Caiman are dispersed amongst a wide expanse of its range. The dry season occurs from September through December, and at this stage water levels recede, flooded savannahs dry, and the Black Caimans are more densely congregated in the permanent lakes and rivers.

Crocodilians in general are the most vocal of the reptiles, and M. niger emits vocalizations that sound like rumbling thunder to communicate with conspecifics. And like most crocodilians, M. niger exhibits parental care (Pough 1998, Thorbjarnarson 1998, Thorbjarnarson 1999).

Food Habits

Studies on M. niger's diet are limited, but some have been carried out and the diet shows many similarities to that of the Common Caiman (Caiman crocodilus). This may be due to similar habitats.

Diets can vary depending on the age, size, habitat, and available prey. Mean prey size is usually positively correlated to caiman size.

Fish, such as piranhas and catfish, account for a large part of the adult Black Caiman's diet, as do molluscs. It also preys on aquatic and terrestrial vertebrates, including some mammals such as capybara (Hydrochaeris hydrochaeris). Young individuals tend to eat insects, crustaceans, and other invertebrates, but many of these are usually replaced in the diet as the caiman matures. Much hunting is done in the water, but the Black Caiman may emerge to hunt on land as well, usually at night (Britton 1999, Da Silveira and Magnusson 1999, Magnusson 1987).

Economic Importance for Humans: Positive

As the largest predator in the 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. Its disappearance from the Amazon would leave a large ecological gap, with adverse effects for its habitats.

If populations recover sufficiently, the Black Caiman could provide economic benefits through controlled hunting for meat. This would give local peoples more incentive to protect the species (Thorbjarnarson 1998, Thorbjarnarson 1999).

Economic Importance for Humans: Negative

There have been claims that the caimans consume large quantities of commericial fishes, having a negative impact on local fishermen, but analysis of stomach contents in one study indicated only small volumes of such fish are eaten at any one time. This does not support the fishermen's claims, and the Black Caimans probably do not significantly affect local fishing.

The Black Caiman will on occasion prey on domestic animals, and there have also been attacks on humans. (Britton 1999, Da Silveira and Magnusson 1999).

Conservation Status

While it was once extremely common throughout its range, commercial hunting has devastated populations of M. niger. Killing black caimans for their skins, which produce a shiny black leather, increased dramatically during the 1940s and 1950s as populations of other, more popular, South American crocodilians were decreasing. Hunting continued through the 1970s, nearly destroying many communities. It is estimated that black caiman populations have been reduced by 99% during the 20th century.

Illegal hunting remains a problem today, but it is not the only threat facing black caimans. The destruction of its habitat by deforestation and burning of swamplands is slowing the recovery of populations, as is increased competition for resources with Caiman crocodilus.

While still present in much of its range, populations are still severely depleted in 4 of the 7 countries in which it occurs. There are some locally strong populations in Peru, Ecuador, Brazil, and Guyana; these tend to occur in isolated, hard to reach areas of swampland. Thorbjarnarson and Da Silveira (1998) found a surprisingly robust population in the Mamiraua Reserve in the Amazon.

The lack of reliable census information makes population surveys a crucial first step for any management program. Ecological studies are also being carried out to help reveal the behavior of this poorly understood reptile.

Management strategies are focusing mainly on legal protection of wild populations, but such laws are not always effectively enforced. Bolivia pioneered a captive breeding and reintroduction program in 1990 by releasing 25 ranch-raised adult black caimans; some of these were observed to reproduce. There is hope that sufficient protection and population recovery may allow the implementation of a contolled, managed harvest that would benefit the local peoples. This would encourage protection of the species as a valuble resource and ease the pressures from uncontrolled poaching. (Britton, September 15, 1999; Thorbjarnarson, 1998; Thorbjarnarson, July/August 1999)

Contributors

Rose Sydlowski (author), Michigan State University, James Harding (editor), Michigan State University.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

freshwater

mainly lives in water that is not salty.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

References

Britton, A. September 15, 1999. "Melanosuchus niger (SPIX, 1825)" (On-line). Accessed November 7, 1999 at http://www.flmnh.ufl.edu/natsci/herpetology/brittoncrocs/csp_mnig.htm.

Da Silveira, R., W. Magnusson. 1999. Diets of Spectacled and Black Caiman in the Anavilhanas Archipelago, Central Amazonia, Brazil. Journal of Herpetology, 33: 181-192.

Da Silveira, R., W. Magnusson, Z. Campos. 1997. Monitoring the distribution, abundance and breeding areas of Caiman crocodilus and Melanosuchus niger in the Anavilhanas Archipelago, Central Amazonia, Brazil. Journal of Herpetology, 31: 514-520.

Herron, J., L. Emmons, J. Cadle. 1990. Observations on reproduction in the Black Caiman, Melanosuchus niger. Journal of Herpetology, 24: 314-316.

Magnusson, W. 1998. Crocodiles and Alligators. Pp. 224-233 in H Cogger, R Zweifel, eds. Encyclopedia of Reptiles and Amphibians. San Diego, CA: Academic Press.

Magnusson, W., E. Viera da Silva, A. Lima. 1987. Diets of Amazonian Crocodilians. Journal of Herpetology, 21: 85-95.

Pough, H., R. Andrews, J. Cadle, M. Crump, A. Savitzky. 1998. Herpetology. Upper Saddle River, NJ: Prentice-Hall.

Thorbjarnarson, J. 1998. "Melanosuchus niger" (On-line). Accessed November 12, 1999 at http://www.flmnh.ufl.edu/natsci/herpetology/act-plan/mnige.htm#TOP.

Thorbjarnarson, J. July/August 1999. The Hunt for the Black Caiman. International Wildlife, 29: 12-19.