When perceiving something as a threat, ground squirrels will emit a whistle-like call as an alarm call. The alarm call comes in two forms; the short and shrill "bi-jo" which signals serious danger, and a medium-pitched "bi-joo" sound which is used for lesser dangers.
When ground squirrels detect a threat, they emit an alarm call that includes both short and sharp "bi-jo" for serious dangers and medium-pitched "bi-joo" for lesser threats.