Hold On to Your Nuts

American red squirrel

The squirrel family is a particularly large one, with almost 300 recognised species. About half of these are ground squirrels of various kinds, including such animals as prairie dogs and marmots. The remainder are tree squirrels, which can be found on every tree-bearing continent bar Australia. Tree squirrels aren't a single group in evolutionary terms, because chipmunks are closer to marmots than to, say, fox squirrels, but they do at least have a fair bit in common.

Life for tree squirrels isn't too bad if they happen to live in the tropics, where trees provide abundant food year round. (The Indian palm squirrel has the added advantage of being a sacred animal in Hinduism, but that's another matter). It's all a bit tougher when they live somewhere with proper winters. By and large, tree squirrels don't hibernate - although many ground squirrels do - which means that those in the north need some way to keep eating throughout the year.

The solution for many, as is well known, is to hide nuts, seeds, and other easily preserved food sources in caches, and return to them when the weather gets bad. This can be important in seed dispersal, should the squirrel forget where it put the hoard, or die from some other cause before it can eat it all.

In Britain, the native tree squirrel, and, indeed, the only native squirrel of any kind, is the red squirrel (Sciurus vulgaris). Since the 1870s, however, it has been under increasing pressure from larger, foreign squirrels introduced from the United States. These are eastern grey squirrels (Sciurus carolinensis), simply called "grey squirrels" in Britain, on the grounds that there's no other sort. Over the last 140 years or so, they have almost entirely extirpated red squirrels from England and made a good start on Wales and Ireland, too.