Many animals become motionless when faced with a predator, a behavior often described as “playing dead.” This dramatic survival strategy occurs across the animal kingdom. Understanding this defense requires examining the underlying biological reflex that governs such extreme responses in threatened species. This instinctual mechanism is triggered only in the most dire circumstances.
The Direct Answer Tonic Immobility in Squirrels
Squirrels, like many vertebrates, can enter a state known as tonic immobility (TI), also called thanatosis or death feigning. This is an involuntary, temporary state of profound motor inhibition, not a deliberate choice to “act dead.” TI is a secondary defense mechanism, typically activated only after primary escape attempts have failed. This innate reflex renders the animal unresponsive to external stimuli. The strategy works by exploiting a common predator trait: a preference for fresh prey and a tendency to stop attacking an animal that appears lifeless.
Triggers and Appearance
Tonic immobility is usually initiated when a predator makes physical contact, such as during an imminent attack or capture. The primary triggers are intense tactile stimulation and physical restraint, signaling an inescapable threat. This extreme stress response causes the squirrel to become completely still and limp, often losing its ability to roll itself back onto its feet. During this state, the animal exhibits complete stillness and a lack of response to external stimuli. Breathing may become shallow, and muscle tone changes, resulting in a rigid or limp posture. This appearance of being dead is intended to cause the predator to momentarily lose interest, providing an opportunity for the squirrel to escape once the threat has passed.
Other Survival Strategies
Tonic immobility is a rare, last-resort action, as squirrels rely far more on active defense mechanisms. Their first response to danger is immediate flight, using agility to run and climb into the safety of trees or burrows. If a predator is detected from a distance, a squirrel will often use freezing, remaining motionless to avoid detection and assess the threat. The species also uses complex vocal communication as a primary defense, issuing specific alarm calls to warn others in the area. These vocalizations are often paired with rapid tail-flicking, a visual signal that helps spread the warning and coordinate escape to a safe refuge.