Publication Date



Open access

Embargo Period


Degree Type


Degree Name

Doctor of Philosophy (PHD)


Biology (Arts and Sciences)

Date of Defense


First Committee Member

Steven Green

Second Committee Member

Richard Tokarz

Third Committee Member

Carl Gerhardt

Fourth Committee Member

Keith D. Waddington


Crocodilians (crocodiles, alligators, caimans and gharials) have a particular category of signals used for long-distance communication of location and status. These signals are composed of acoustic and non-acoustic components with different physical properties, such as vocal sounds, slaps, infrasound, odor and postures. A survey of extant species and a comparative study of allopatric conspecific populations inhabiting different habitats show that the composition of these signals is adjusted to optimize their ability to carry information in each habitat. Studies of animals living in changing habitats and of animals inhabiting different habitats within the same geographical areas show that these adaptations are evolved differences between populations and species rather than a result of behavioral adjustments by individual animals in response to habitat structure. Details of adjustment process help elucidate information about the functions of each signal component. Experimental data obtained in the course of the study show that crocodilians have the ability to locate the sound underwater. In addition, novel information on signaling by almost all extant crocodilian species is provided. This information gives important new evidence for solving the long-standing controversy of crocodilian systematic, showing that false gharials are aberrant crocodiles rather than members of the gharial lineage. It also sheds some light on the evolution of crocodilian signaling, allowing to plot the events of signal evolution on the phylogenetic tree, and explaining the puzzling absence of small species among extant crocodilians.


crocodilians; signaling; evolution; bellow; roar; infrasound