PS 74-17 - Tail signals in eastern gray squirrels include both generic and predator-specific alarms

Friday, August 12, 2011
Exhibit Hall 3, Austin Convention Center
Thaddeus R. McRae, Science, Broward College, Coconut Creek, FL

Alarm signals, used by many prey species, may function as generic warnings or contain information about predator type.  Such predator-specific alarm signals are predicted to occur in prey species that have different escape strategies for different predator types. Eastern gray squirrels (Sciurus carolinensis) are preyed on by aerial and terrestrial predators and may use predator-specific strategies to avoid each type of predator. Gray squirrels are known to use several vocalizations and tail signals as alarms. To test whether amplitude of tail signals (small or large) is associated with predator type (aerial or terrestrial), individual squirrels were presented with two moving model predators, namely hawk and cat, and three kinds of controls, namely a red ball approaching through the air, a red ball on a radio-controlled base, and the radio-controlled base by itself.


Squirrels always ran up a tree in response to the moving object, whether model predator or control. Once in the tree, they usually used tail signals. Small tail signals were generic alarm signals; there was no association of small tail signal use with the object presented. In contrast, large tail signals showed a strong association with object type, suggesting that gray squirrels discern the specific threat and modify their response accordingly. The association is largely due to an inhibition of large tail signals in response to the model hawk. It may be that squirrels are modifying their alarm signal to avoid drawing attention to their location. When facing a terrestrial predator the squirrel is safe from attack once it is in a tree and uses large tail signals, thereby advertising its location with impunity. However, an aerial predator can pluck a squirrel right out of a tree, so in the presence of a hawk the squirrel may benefit from using only small tail signals that may be less likely to attract a hawk’s attention.

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