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They are devoted parents, more so than other non-avian reptiles.
Since crocodilians began to be studied scientifically three hundred years ago, research on their social behavior has proceeded slowly and only recently. A method to determine their sex wasn't devised until 1963. In the 1980s, while other scientists were starting to revise our view of dinosaurs, a few biologists began to look more closely at this other group of archosaurs.
From observed social behavior, researchers found that crocodilians are usually devoted parents. Mother crocodilians go through considerable effort to create nests, using mounds of rotting vegetation and mud to deposit their eggs. Spectacled caimans (Caiman crocodilus) and some other crocodilians make similar nests. American crocodiles (Crocodylus acutus) dig holes in sand, similar to turtles. Gharials (Gavialis gangeticus) and many other crocodilians do the same, laying their eggs to incubate underground. Sometimes crocodilian mothers nest in proximity to each other. Crocodilians with sand hole nests have been observed more often nesting near each other than mound-nesting animals. This finding could be caused by the paucity of good banks for digging nests or by data collection bias, or it could mean these crocodilians are more social. Either way, all crocodilians time their nesting or the hatching of their nests based on the rainy season for their particular location.
After eggs are laid, maternal crocodilians remain nearby. In the case of gharials, fathers may also remain close, and there is inconclusive evidence that other male crocodilians may remain in the immediate area. How much aggression mothers display toward intruders depends on the species and individuals involved, but it is thought that an adult female's mere presence might convey some protection to her unhatched young.
Crocodilians are the most vocal of non-avian reptiles. Experiments in laboratory incubators have shown that alligators and crocodiles vocalize during the last two weeks before hatching and will respond to each other's cries. When egg containers are tapped, embryos answer with pecking noises. Calls from young animals, when played back to mothers, showed that most crocodilian calls are understandable among different lineages of the group. A mother American alligator, for example, can understand the calls of a young American crocodile and vice versa. This characteristic suggests that dinosaurs and ancestral crocodilians were vocal.