males project an infrasonic signal

Crocodiles are the most social of reptiles. Even though they do not form social groups, many species congregate in certain section of a rivers, tolerating each other at times of feeding and basking. Most species are not highly territorial, with the exception of the saltwater crocodile; which is a highly territorial and aggressive species. A mature male will not tolerate any other males at any time of the year. Most of the species however, are more flexible. There is a certain form of hierarchy in crocodiles, where the largest and heaviest males are at the top; having access to the best basking site, females and priority during a group feeding of a big kill or carcass. A good example to the hierarchy in crocodiles would be the case of the Nile crocodile. This species clearly displays all of these behaviors. Studies in this area are not thorough, and many species are yet to be studied in greater detail.[55] Mugger crocodiles are also known to show toleration in group feedings and tend to congregate to certain areas. However males of all species are aggressive towards each other during mating season, to gain access to females.
Crocodiles are also the most vocal of all reptiles, producing a wide variety of sounds during various situations and conditions, depending on species, age, size and sex. Depending on the context, some species can communicate over 20 different messages through vocalizations alone.[56] Some of these vocalizations are made during social communication, especially during territorial displays towards the same sex and courtship with the opposite sex; the common concern being reproduction. Therefore most conspecific vocalization is made during the breeding season, with the exception being year-round territorial behavior in some species and quarrels during feeding. Crocodiles also produce different distress calls and in aggressive displays to their own kind and other animals; notably other predators during interspecific predatory confrontations over carcasses and terrestrial kills.
Specific vocalisations include -
Chirp: When about to hatch, the young make a “peeping” noise, which encourages the female to excavate the nest. The female then gathers the hatchlings in her mouth and transports them to the water, where they remain in a group for several months, protected by the female[57]
Distress call: A high-pitched call mostly used by younger animals that alerts other crocodiles to imminent danger or an animal being attacked.
Threat call: A hissing sound that has also been described as a coughing noise.
Hatching call: Emitted by females when breeding to alert other crocodiles that she has laid eggs in her nest.
Bellowing: Male crocodiles are especially vociferous. Bellowing choruses occur most often in the spring when breeding groups congregate, but can occur at any time of year. To bellow, males noticeably inflate as they raise the tail and head out of water, slowly waving the tail back and forth. They then puff out the throat and with a closed mouth, begin to vibrate air. Just before bellowing, males project an infrasonic signal at about 10 Hz through the water which vibrates the ground and nearby objects. These low-frequency vibrations travel great distances through both air and water to advertise the male's presence and are so powerful they result in the water appearing to 'dance