More bang for your buck: the effect of caller position, habitat and chorus noise on the efficiency of calling in the spring peeper

Abstract

Many animals use acoustic signals as a means of intra- and inter-specific communication. For example, male anuran amphibians produce advertisement calls to attract females for breeding, and as a territorial signal. The production of acoustic signals can be energetically costly, and the distance over which a signal is effective depends on a range of variables including the location of the caller and receiver, ambient conditions and the habitat through which the sound travels. This paper presents a spatially explicit model of the propagation of an anuran advertisement call across a landscape, using the example of the northern spring peeper Pseudacris crucifer crucifer. The model is used to investigate (a) the effect of habitat, caller position and chorus noise on the effective distance of a call with a frequency of approximately 3 kHz; and (b) the energetics and efficiency of calling at different intensities and from different locations in the landscape. Calling next to still water or from an elevated perch increases, while calling in a chorus decreases, the distance over which a female can distinguish an individual male's call. For a given call intensity and calling rate, a male spring peeper will get the greatest “bang for its energetic buck” if it calls next to still water in the absence of chorus noise. However, when a chorus of spring peepers is gathered at a pond, calling from an elevated position away from the pond (and the chorus noise) will maximise the effective distance of an individual call, although this may entail other costs. The model presented here is the first realistic, interactive mathematical model of the propagation of animal sounds across a landscape, and uses a gis interface to display the effect of habitat and caller position on animal communication. It has applications for both research and teaching, and a copy can be obtained free of charge by contacting the author.