Arctic ground squirrels, Citellus undulatus, produce six distinctly different sounds. Each of these sounds may represent a signal in itself, but combinations of these acoustic elements or repetition of a single element produce additional signals. Several of these signals serve as alarm calls. One sound element consists of a short (0.05 sec) broad frequency chat while another is a longer (0.16 to 0.25 sec) descending narrow frequency whistle. Squirrels utter three-note chatter calls when approached by a ground predator, and a series of five or more chatters, which fade in intensity, is given upon the close approach of a ground predator as the squirrel escapes into a burrow. A single whistle, which resembles the alarm call of some birds, is given upon the approach of an aerial predator. This call is repeated at approximately six to eight second intervals if the predator alights near a squirrel and remains nearby.