john w. anderson, a professor in the department of zoology at cornell university, was the first to discover that rats were capable of emitting ultrasonic vocalizations. he used a sonic amplifier to observe these vocalizations, and could not be sure of their function. however, he hypothesized that these vocalizations could help rats to communicate amongst themselves and/or orient themselves in their environment, similar to bat echolocation. this hypothesis was put to the test a number of times, but it did not hold up in experimental testing. there were several studies supporting the fact that rats use echolocation, but ultrasonic vocalizations were not involved. other studies have proposed that ultrasonic vocalizations are by-products of a rat’s physiological response to temperature (for example, helping to return venous blood to the rat’s heart). however, it has now been widely accepted that rats emit ultrasonic vocalizations as social signals. it is important to note that ultrasonic vocalizations are not exclusive to rats. other rodents such as mice emit such vocalizations, as well as bats.