A squirrel's nest is called a drey
lungs
squirrel
A group of squirrels is called a dray or a scurry. Squirrels do not spend much time in large groups. Usually, just a family group of three or four will be together for any significant length of time.
I think it is called a lair
Raccoons have a den, not a nest.
They are called lairs, dens, burrows or earths.
A group of flying squirrels is called a "Dray".
Tree-dwelling squirrels require trees to escape danger, to den, and for a source of food. Without them, they cannot survive. There are ground squirrels that don't depend on trees, but they are specially adapted for a ground-dwelling lifestyle.
An otter's den is called a holt or a couch.
So that they have somewhere to live and to raise their kits.
den
It is called a lair, a den, a burrow or an earth.
A bird-watcher's den is called a HIDE.
A rabbit den is called a warren.
lungs
yes there is a whole species called the Mexican Flying Squirrels
a den in a tree is called a nest.