A literature review and field observations indicate that most sciurids are facultative predators on small vertebrates. This behavior is documented for at least 30 sciurid species in 8 genera. The frequency of predation apparently is influenced by various factors including climate, season, gender, reproductive condition, and availability of plant sources for certain nutrients such as calcium and nitrogen. Although sciurids assimilate as much energy from animal foods as do obligate carnivores, behavior associated with predation appears to be less efficient in sciurids and may rely partly on prey habituation and other adaptive behaviors.
Callahan, J. R.
"Squirrels as predators,"
Great Basin Naturalist: Vol. 53
, Article 5.
Available at: http://scholarsarchive.byu.edu/gbn/vol53/iss2/5