Red-cockaded Woodpeckers are unique among woodpeckers in that they excavate their roost and nest cavities entirely within living pines. Studies show that there is a propensity for squirrels to use unenlarged cavities, none have shown evidence of Red-cockaded Woodpeckers being killed by southern flying squirrels. However, we report an instance of two nestlings found dead at the base of the nest tree and 3 flying squirrels inside the nest cavity.
McCormick, J. R., R. N. Conner, D. Saenz and D. B. Burt. 2004. Evidence of red-cockaded woodpecker nestling displacement by southern flying squirrels. Bulletin of the Texas Ornithological Society 37:8-9.