Do individual crocodilians adjust their signaling to habitat structure?

Abstract

All crocodilians use long-distance signals, composed of infrasound, vocal sounds and/or slaps. These components differ in their ability to carry information about the animal's location and status through air and water. It has been previously shown that signal composition differs between species and allopatric conspecific populations; species and populations living in fragmented aquatic habitats use more vocal signals and/or fewer slaps than species and populations living in continuous aquatic habitats, thus adjusting their signaling to habitat structure. There are two possible mechanisms for such adjustment: behavioral plasticity and evolved differences between species and populations. In the present study, it is shown (a) that individual yacare caimans (Caiman yacare) do not change the composition of their signals in response to changes in aquatic habitat continuity, and (b) that in areas where both continuous and fragmented aquatic habitats are available, American alligators (Alligator mississippiensis) and Nile crocodiles (Crocodylus niloticus) living in small bodies of water do not differ in signal composition from those living in large bodies of water. Therefore the previously found differences in signaling between species and between allopatric conspecific populations are evolved adaptations rather than behavioral responses by individual animals.