Friday, 19 May 2017

In both love and war, alligators signal size by bellowing




Date: May 12, 2017
Source: University of Vienna]

In alligators and other crocodilian species, being bigger than your conspecifics 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 so it would be advantageous if fights could be avoided by individuals reliably signalling their body size to potential mates and rivals early on. One way to achieve this is by "honest" acoustic cues to body size in vocalizations. A team around Tecumseh Fitch at the Department of Cognitive Biology at the University of Vienna has now identified cues to body size in calls of American alligators, which is the first finding of this kind in reptiles.

American alligators produce very low-pitched rumbling roars, so called "bellows," year-round and most frequently during mating season. Interestingly, the bellowing displays differ between the sexes, as study co-author Kent Vliet from the University of Florida had previously described: Only male alligators produce a "water dance," visible due to water droplets sprinkling over their backs, preceding the audible bellow.

For the current study, lead-author Stephan Reber and Judith Janisch of the University of Vienna recorded the bellows of 43 adult American alligators at the St. Augustine Alligator Farm Zoological Park in Florida. Then the curators of the institution, Kevin Torregrosa and Jim Darlington, together with the two researchers, measured the head and total body length of all the alligators up close with measuring tapes and hand-held laser-distance-measurement devices.


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