DOES BRANTS' WHISTLING RAT (PAROTOMYS BRANTSII) USE AN URGENCY-BASED ALARM SYSTEM IN REACTION TO AERIAL AND TERRESTRIAL PREDATORS?

Abstract

Abstract It is predicted that differences in mammalian alarm call systems may be explained relative to the complexity of their habitat, with species inhabiting three-dimensional habitats classifying predator types (externally referential), and those living in two-dimensional environments indicating the level of risk (urgency-based). We tested this prediction in a two-dimensional environment for a small African rodent, Brants' whistling rat, Parotomys brantsii. Colony members were presented with predator models of a raptor and puff adder, as well as a human observer, to investigate their alarm call repertoire. Alarm calls consisted of simple, singlenote vocalizations, often repeated in non-rhythmic bouts. Virtually no variation was detected in the structure of alarm whistles between the calls elicited by the two model predators and humans, indicating that P. brantsii did not identify different predator types by means of vocalizations. However, note duration was dependent on the reaction of the caller: when the caller bolted towards safety, the whistle was significantly shorter than when it remained stationary. A snake and far-off human elicited relatively long-duration calls and the caller would remain above ground, signifying a low-risk situation. High-risk encounters with a nearby raptor or human provoked short calls before the whistling rat bolted underground. We conclude that P. brantsii's alarm call repertoire represents a graded 'urgency-based' system, indicating perceived threat level rather than predator type. Our study supports the prediction that mammalian alarm call systems in two-dimensional environments primarily provide information indicating the level of risk and not predator type.