Although echolocation is classically associated with bats and dolphins, many animals produce ultrasonic and/or click-like signals to potentially navigate their environment. Shrews (Soricidae) are thought to rely on ultrasonic signals for echo-orientation, producing both ultrasonic click-like signals and tonal twittering signals. Recently, the role of ultrasonic clicks in shrew echo-orientation has been questioned, as these clicks have been proposed to be artifacts of shrews moving throughout their environment. By combining infrared video and ultrasonic audio recordings, we investigated the acoustic signals made by shrews (Blarina brevicauda) during different periods of locomotion. We hypothesized that if shrews are using ultrasonic vocalizations as a sensory mechanism, they will display head scanning behavior while emitting clicks that share key characteristics with other known echolocating animals. Our results show that B. brevicauda predominantly emit ultrasonic clicks rather than ultrasonic twittering calls while exploring a new environment, with clicks having the following characteristics: less than 120 μs in duration, median peak frequency of 26.9 kHz, and median bandwidth of 22.9 kHz. Across individuals we found no significant difference in peak frequency. Our results indicate that shrews emit ultrasonic clicks in novel environments which further supports the hypothesis of echo-orientation or echolocation in shrews.
