Due to a lack of field studies, very little is known about the behaviour and ecology of the broad-snouted caiman, and much of what is known about its reproduction has come from captive individuals in zoos (6).
The broad-snouted caiman nests during the rainy season (August to January in Brazil, January in Uruguay, and January to March in Argentina), when decaying vegetation is collected from around a nest site and scraped into a mound (2) (5). The male assists with constructing the mound nest, but the female becomes more aggressive as incubation continues, and only the female tends the nest (5). Around 20 to 50 eggs, or as many as 90 in some locations, are laid in two layers in the nest, with the layers separated by vegetation (5). This layering of the eggs may help to create a slight difference in temperature within the nest and a slightly different sex ratio in the embryos (7), since only females are produced between 29 and 31 degrees Celsius, only males are produced at 33 degrees Celsius, and both males and females are produced at 34.5 degrees Celsius (8). After an incubation period of around 63 to 70 days, the female breaks open the nest and carries the hatchlings in her mouth to the water. For their first year, the hatchlings cluster in the water close to the nest, all the time being closely attended by both the adults as protection from predators (5).
The broad-snouted caiman has a varied diet that includes shrimp, fish and birds (7), but in some parts of its range it feeds mainly on snails (6). To maintain its body temperature, it basks for about 30 minutes on summer mornings and for up to 4 hours in spring and autumn, often with an additional period in the late afternoon. It is only active on sunny days during the winter. The broad-snouted caiman can apparently survive colder temperatures than other crocodilians in the region, and its dark colour may be an adaptation to this, as darker colours are better at absorbing light which is converted to heat (5).