Body Proportions and Gliding Adaptations of Flying Squirrels (Petauristinae)

Flying squirrels range in length of head and body from less than 90 mm to more than 400 mm. Large flying squirrels are more slender than tree squirrels or small flying squirrels. They have proportionately longer tails than small flying squirrels, but large tree squirrels have the longest tails of all, both absolutely and proportionately. Relative limb lengths decrease with size among flying and tree squirrels, but the ratio of forelimb to hindlimb length is generally higher for flying squirrels than for tree squirrels. The styliform cartilage adds to the area of the patagium, but it is isometric with respect to size. Weight varies by a factor of almost 64 and the area of the patagium by a factor of almost 16, with little divergence from the expected isometric relationship. Therefore “wing loading” varies almost by a factor of four and is estimated to be as low as 30 Newtons/square meter (N/m2) in small petauristines and as great as 110 N/m2 in large ones. Hang gliding seems to provide a good analogue for the gliding of flying squirrels, although the squirrels have lower aspect ratios (l.0 to 2.2) and lower glide ratios (less than 3) than do most hang gliders. From this analogy it seems probable that the heavier “wing loading” of large flying squirrels does not affect the glide ratio (horizontal distance/vertical drop) but that the larger flying squirrels must “fly” faster to maximize their glide ratio. It is also probable that small flying squirrels with lower “wing loadings” are more maneuverable, but large flying squirrels with heavier loadings are less affected by air turbulence.