Many animals advertise the presence of a predator threat through vocal signals. Black-capped Chickadees (Poecile atricapilla) use their chick-a-dee call as a mobbing call when encountering a perched hawk or owl. This social signal appears to serve as an alert to other chickadees, causing them to rally to the vicinity of the predator and join in a chorus of calling. We asked the question: do chickadees vary the mobbing call in a manner that could convey the immediacy of threat from a potential predator? We examined the responses of chickadees to a taxidermic mount of an avian predator presented at distances of 1 m and 6 m from each subject. Vocal responses were recorded and analyzed for response latency, calling rate, and syllable composition of calls. During 5-min trials, the subjects responded more quickly and produced significantly more chick-a-dee calls for predator presentations at the 1-m distance than at the 6-m distance. Alterations of syllable composition of the call also were observed under the two treatments. These results suggest that information about the immediacy of threat or proximity of a predator may be signaled by alteration of the rate of calling, with possible additional information contained in proportional changes in the different syllable types of the call. Studies of referential (symbolic) communication in birds and mammals often have failed to consider the problem of response urgency separately from predator-type labeling in vocal signal design.