As of November 2026, the black caiman is the largest kind of caiman, and it lives in the slow rivers, lakes and flooded land of the Amazon. In Mamirauá Reserve, scientists counted caimans by boat at night from 2008 to 2023, at a steady 15 kilometres an hour with flashlights. Relative abundance is the number of caimans counted for each kilometre travelled.

In the 2023 drought in Mamirauá Reserve, 240 caimans were counted per kilometre, against a 2008 to 2022 average of 44, and a figure caption notes a pronounced rise in black caiman counts. The absolute number of caimans counted in 2023 was 4,412, close to the yearly average, because the survey covered much less distance. The authors link the higher count to the loss of water habitat in the drought, and say their methods cannot show that the caiman population grew. The drought year also had approximately 10 caiman nests per lake, against the usual 7.

A study in Mamirauá Reserve looked at nesting female black caimans, which were approximately 135 centimetres from snout to vent on average. Nesting females build nests close to the water and are usually in the water, where they have access to food. The authors write that no information is available on the diet of nesting female black caimans. Nests are mounds of earth, leaves and sticks, mostly in flooded forest around lakes cut off from the river, and black caimans nest every year in the dry season.

In a drought, a black caiman may stay buried in the mud on the bottom until the rains return. Its home range can be under 1 hectare in the low-water season and grow to 20 hectares in the rainy season. A hectare is a large land area, so the same caiman may use very different amounts of space as the water changes.

Words to know

• abundance: how many
• drought: long dry spell
• hectare: large land area