1,141 mammal species – 25 per cent of those known to science...
Q&A: Squirrel tail propulsion?
BBC Wildlife reader Bill Earl filmed a grey squirrel jumping and wanted to know whether it was using its tail for propulsion. Mammal expert Steve Harris answered his question.
Grey squirrels often pump their tails during take-off and in flight, but it’s never been proved that this aids propulsion.
Your footage, however, does seem to show the animal accelerating in mid-air, though we don’t know the rate of acceleration or what it is gaining in distance.
Grey squirrels are well adapted for jumping. Long, flexible toes help them to grip on landing, and they can rotate their hind feet, enabling them to descend a tree trunk headfirst with their hind feet pointed backwards for purchase, which maintains their speed.
Squirrels also have excellent eyesight. Unlike humans, they have sharp focus across the whole retina, and pale, yellow-tinted eye lenses that reduce glare from bright light and increase contrast – assets when moving rapidly through the trees.
Their tails are equally well designed. The vertebrae at the base of the tail are shorter than the rest, creating numerous joints that give plenty of flexibility.
Moreover, the tail hairs are arranged in a distinct way, with lateral hairs longer than those at the top and bottom. This feather-like shape enhances wind resistance and gives greater manoeuvrability when leaping, helping with steering, balance and slowing the descent.
Steve Harris is a mammal expert and regularly contributes to BBC Wildlife.