"Squirrels, in theory, can survive a fall from virtually any height. 

Instinctively spreading their bodies when falling, squirrels create wind resistance, slowing their rate of descent, while their fluffy fur acts as a cushion. However, it’s their size and mass that make them expert ‘fallers.’ 

I’m no scientist (and it’s pretty scientific), but acceleration due to Earth’s gravity is always the same, regardless of the object on which it’s acting. Since a squirrel isn’t very heavy (grey squirrels weigh about 0.5 kg) the force acting on it is small. 

Force = mass*acceleration = 0.5 kg * 9.81 m/s2 = 4.9 N

For these reasons, the fastest speed a squirrel will fall (known as terminal velocity) is low enough that they’ll never fall hard enough to sustain fatal injuries… at least hypothetically."