From Oaxaca, Mexico, at a meeting of the Animal Behavior Society
Richardson's ground squirrels may squeak out ultrasonic calls when sensing danger, thereby alerting nearby squirrels but minimizing the noise that might be detected by predators.
Ultrasonic communication has been reported in other rodent species, though not as threat warnings, says David Wilson of the University of Manitoba. He and James Hare recorded high-pitched sounds at about 50 kilohertz from 15 ground squirrels that were exposed to a disturbance. To a person watching a video of one of the episodes, the ground squirrel seems to be opening its mouth without making noise.
Wilson then broadcast the recordings to different groups of the squirrels and monitored them for raised heads and other signs of vigilance. The ultrasonic calls did rouse hearers to increased vigilance, although not as dramatically as recordings of audible warning calls did, say the researchers.