Crocodilians have important forms of communication in their behavioral repertoire that are sometimes little noticed due to the subtlety of their execution. Whether it's for specific interaction with those who live in the same group, mating, intimidating possible threats or even simple movements, such as arching their tails and heads, communication and the execution of sounds is part of the ethology of these reptiles and an important part of their survival.
Normally, when studying the subject, the sounds emitted by crocodilians are classified into two types: firstly, there are the vocals, which are those strong sounds audible to humans, called "bellowing" or roars. Vocal communication is more common in animals from the Alligatoridae and Crocodylidae families and is usually performed out of water; the other type is infrasound, which is characterized by non-vocal vibrations, usually performed underwater. Curiously, they are below the frequency range of human hearing, but are capable of propagating in water over great distances. Thus, infrasound is an important communication tool for these animals in the aquatic environment, and is normally produced at 140 dB, depending on the size of the individual.
However, these vibrations lose their usefulness outside bodies of water, as they do not propagate optimally in the air and are absorbed by the terrestrial boundaries of aquatic habitats. Furthermore, the production of infrasound is characterized by the rapid displacement of large volumes of water, and it is theorized that carrying out these movements requires considerable force and a lot of energy.
Due to the characteristic of infrasound propagation in water, it is theorized that the composition of the habitat and the characteristics of the bodies of water are directly linked to the ability of each species to deal with these vibrations. Dinets (2011) compares the communicative components of crocodilians, hypothesizing that for species in which the aquatic habitat is more fragmented, infrasound is used less than in those in which the fluvial environment is more continuous. On the other hand, the use of vocal communication is more common for species found in non-continuous aquatic habitats. In addition, other studies, such as Vergne (2008), also raise questions and hypotheses about communication between crocodilians, especially infrasound: it is argued that the hearing of these animals does not show significant evidence of being sensitive and able to hear sounds of minimal frequencies, such as infrasound. Therefore, it is theorized that the perception of information would be linked to mechanoreceptors in the skin and not to neuroauditory components as previously thought.
Although studies on the subject are becoming more and more frequent, there are still many gaps in this communication. There are many questions about the anatomy and functionality of hearing in this order of animals, as well as how infrasound is picked up and interpreted, at what age it becomes an efficient mechanism and whether crocodiles can accurately locate the source of the vibrations.
Gustavo Gomes da Luz Pereira
Secretariat Director
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