Squirrels, particularly ground-dwelling species, use non-vocal communication methods like foot tapping, foot drumming, and tail flagging. This behavior is a form of seismic signaling, where vibrations are generated by striking the ground. The drumming is an intentional signal that communicates different messages depending on the context and the species involved. This physical action allows squirrels to communicate with other individuals or directly with a potential predator without relying on sound alone.
Communication of Immediate Danger
One primary function of foot drumming is to broadcast an alarm signal about a generalized threat. When a squirrel spots a predator, such as a coyote, fox, or hawk, it rapidly thumps its hind feet on the ground. The resulting vibrations travel through the ground, which is an effective medium for long-distance communication. These seismic waves alert nearby squirrels that danger is present and that they should seek shelter quickly. The signal encourages conspecifics to retreat into a burrow or climb a tree to safety, increasing the collective vigilance of the group.
Asserting Territorial Dominance
Foot tapping also functions as an agonistic display directed toward rivals and intruders. When a squirrel perceives a threat to a valuable resource, such as a cached food supply or a mating partner, the foot drumming becomes a challenge. This behavior establishes a boundary and asserts the individual’s willingness to defend its space. This display is often accompanied by an aggressive posture, such as standing tall on the hind legs, and vigorous tail flagging. The combination of seismic communication and visual signaling acts as a composite threat display, signifying the squirrel’s dominance to a competitor.
Detection and Response to Subterranean Threats
The most complex and targeted use of foot drumming involves active deterrence and detection of specific threats, particularly the rattlesnake. Studies on species like the California ground squirrel reveal an evolutionary arms race with this venomous predator. The squirrel uses its foot tapping to create vibrational communication, which helps it gauge the location and potential size of a hidden snake.
When confronting a rattlesnake, the squirrel employs a unique, multimodal signal that includes heating its tail and flagging it from side to side. The squirrel actively shunts warm blood into its tail, increasing its temperature by several degrees to create an infrared signal. This thermal display is specifically targeted at the rattlesnake’s pit organs, which are heat-sensing receptors that the snake uses to locate warm-blooded prey in the dark.
By heating and flagging its tail, the squirrel exploits the snake’s sensory system, making itself appear larger and more threatening through thermal imagery. This action serves as a deterrent, signaling to the snake that the element of surprise is lost, and the squirrel is ready to defend its young.