CROCLIST: Nile croc vocalizations

[Vladimir Dinets]

Adam & Ryan,
I think I should inform you better about what I am trying to do.
I am looking specifically at one type of vocalizations: those produced by adults males and accompanied by infrasound. I have already demonstrated that they differ between species and populations depending on habitat. Species/populations living in small bodies of water use more roars/bellows, while species/populations living in large, continuous bodies of water use more head-slaps. I am pretty sure I figured out the acoustical reasons for that, but explaining them would take a while - I can send you a PP file of my thesis proposal presentation once I get back from Africa if you'd like to have a look.
Now I am trying to figure out how it works: do individuals change their behavior depending on habitat, or does their behavior change over many generations?
I observed yacare caimans in places where water levels change a lot during the mating season, and found that individual animals did not change the percentage of roars vs. head-slaps as their lakes became fragmented (as water levels dropped) or connected to rivers (as water levels rose).
Now I am looking at Am. gators and Nile crocs to see if those differences exist only between populations, or also between animals living in lakes of different size, but within the same area. This will give me an idea about the rate of change.
The interesting thing is, gators and crocs differ in how they choose their signals. Gators almost always use either bellowing display or head-slapping display, while crocs can do any combination. Now it seems to me that they also adapt to habitat differences in different ways: gators change the relative usage of the two display types, while Nile crocs change the signal parameters such as the volume and duration of the roars.
All this is still preliminary results, but I hope to have more substantiated answers and more data within aboout a year.
I have sound recordings of a bunch of species, and would gladly share them if you go forward with the sound library idea.
Vladimir Dinets

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