Image via wired.com.

American alligators produce loud, very low-pitched vocalizations called “bellows”. These rumbling roars communicate the animal’s body size to other alligators. Alligators can use this information to avoid unpromising contests for mates and breeding areas. That’s according to a new study published in Scientific Reports on May 12, 2017
In alligators, being bigger than other alligators can have decisive benefits. Females only accept males larger than themselves as mates and larger alligators are much more likely to win territorial fights. However, direct physical confrontations can lead to lethal injuries. That’s why it’s advantageous if fights can be avoided by alligators reliably signaling their body size to potential mates and rivals early on.
That’s where bellowing comes in. A research team of cognitive biologists at the University of Vienna identified cues to body size in the alligators’ bellows.

A male American alligator bellowing. Sub-audible vibrations produce the “water dance” above the animal’s back. American alligators bellow year-round, but most frequently during mating season. Bellowing differs between the sexes. Only male alligators produce a water dance, visible due to water droplets sprinkling over their backs, preceding the audible bellow. Image via Stephan Reber.