Shrews are vocal mammals. They navigate their world and interact with others through a diverse array of sounds. Their vocalizations offer a glimpse into their lives, revealing complex communication strategies and unique sensory adaptations.
The Sounds Shrews Make
Shrews produce a variety of specific sounds, including high-pitched squeaks, chirps, and trills. They also emit rapid clicking or buzzing noises. Many of these vocalizations, particularly the faint, high-pitched laryngeal twittering calls, are in the ultrasonic range, making them difficult or impossible for humans to hear without specialized equipment. However, some of their sounds, especially when they are territorial, can be audible to the human ear.
Shrew sounds are often low-amplitude, multi-harmonic, broadband, and frequency-modulated. Up to 17 different types of calls have been identified across various shrew species.
Why Shrews Vocalize
Shrew vocalizations serve various communication purposes beyond navigation. They use sounds for territorial marking and defense, warning off other shrews from their space. Because shrews are highly territorial and aggressive, their squeaks and chirps can be particularly noticeable during interactions with rivals.
Sounds are also significant in courtship, with male shrews sometimes producing clicks to attract females. Additionally, shrews make distress calls when they feel threatened or are caught, acting as an alarm to defend themselves or ward off predators. Communication between a mother and her young also involves vocalizations.
Echolocation in Shrews
Echolocation is a fascinating aspect of shrew vocalization, enabling them to perceive their surroundings using sound waves. Shrews emit high-frequency clicks and interpret the returning echoes to build a “sound map” of their environment. This ability is particularly beneficial for shrews, given their poor eyesight and their habits of living in dense undergrowth or being active during low-light conditions.
While bats primarily use echolocation for hunting, shrews mainly employ it for spatial orientation and assessing their habitat, such as identifying routes through tunnels or probing habitat types. The clicks emitted by shrews for this purpose are typically short in duration, broadband, and have a median peak frequency of around 26.9 kHz, aiding in quickly gathering environmental information. This trait is rare among terrestrial mammals, making shrews, along with some tenrecs, unique in their use of an echo-based orientation system.