More extensive information on mammals can be found in a separate blog post.
B. Squirrels (SCIURIDAE)
Squirrels, like rats and mice, are rodents, which are distinguished by a single pair of chisel-shaped incisor teeth in both upper and lower jaws, separated by a gap from a short row of grinding cheek-teeth. They are principally herbivores, with most being principally bud and seed eaters. Rodent footprints show the presence of four toes on the fore feet and five toes on the hind feet.
Squirrel nests (dreys) usually have leaves still attached to twigs, in contrast to rook and magpie nests, which have twigs with no leaves on. Nut shells are split in two, and their gnawing leaves jagged edges. Stripped fir cones also reveal where they have been feeding. Squirrel footprints show the presence of three long central toes on the hind feet, with three palm pads and two heel pads. Squirrel droppings are variable in colour, almost spherical but slightly flattened at one end and slightly pointed at the other. They smell sweetly.
C. Grey Squirrel (Sciurus carolinensis)
Larger than our native red squirrel, the North American grey, introduced in the 1870s, never develops ear tufts, and has white fringes on the more flattened but still bushy tail. They are mainly grey in colour, and often seen foraging on the ground. Their dreys of twigs and leaves are often built on an exposed branch. They have a chattering call, accompanied by rhythmic flicking of the tail. They do not hibernate.
As this is an introduced species, squirrel folklore will refer only to our native red squirrel. The character Pattertwig in C S Lewis's 'Prince Caspian' is a red squirrel, as is Beatrix Potter's Squirrel Nutkin, who outwits Old Brown the owl. Contrary to popular belief the grey does not attack and kill the red, but is a more successful forager in deciduous woodland, especially for green acorns. Red squirrels can't digest mature acorns and therefore lose out in the competition for green acorns, although they fare better in coniferous woods because the greys prefer deciduous rather than coniferous seeds. Grey squirrels carry the Parapoxvirus, which is not fatal to them, but often kills the reds. Also, the breeding potential of reds is reduced by competition, whereas the greys seem unaffected by these stresses.
When the red squirrel was common all over the country it was regularly trapped and eaten, which led to leprosy, a red squirrel disease, becoming widespread in medieval times. People were fearful of touching lepers, whereas in fact leprosy is virtually non-contagious, but it is wise never to attempt to handle red squirrels.