Shrew twittering call rate is high in novel environments—a lab-study

Abstract

Shrews use several different call types for communication. In previous studies, two call types have been additionally associated with a possible function for echolocation: ultrasonic click-like emissions and sonic twittering calls. There is anecdotal evidence that the rate of shrew twittering calls is high in unfamiliar environments and lower in familiar ones. Here we quantitatively tested this assumption for the first time. In a simple laboratory experiment, we confronted three different shrew species with environments of different degrees of novelty. We could show that the twittering call rate indeed decreased with increasing familiarity with the environment. In a separate experiment, we tested if shrews would increase twittering call rate after a stressful event, which they did not. The finding of an increased call rate inside a novel environment that is not caused by stress is in line with the hypothesis of a very basic echolocation-like system in shrews, as also bats increase their echolocation call rate in novel environments. However, it is not in full agreement with the hypothesis that twittering in shrews mainly has a function for communication, as in territorial signalling, call rates are usually higher in familiar than in unfamiliar environments. Call rates did not change after a small structural alteration inside the familiar environment, suggesting that shrews use their twittering calls not for a fine-tuned echolocation like bats, but rather a coarse acoustic orientation in their surroundings (‘echo-orientation’). Certainly, echo-orientation and communication might be two parallel, non-mutually exclusive functions of shrew twittering.