Treetop acrobat: the secret life of the squirrel

Red squirrels are cherished but greys despised. Is this fair? It’s time to get to know the high-flying world of these two kings of the canopy – and perhaps learn to love them both, says Dominic Couzens

13th September 2017
Red squirrel/Credit: Naturepl.com

Squirrels are so familiar to us that we easily forget that, in common with many wild animals, they are quite alien in body form and senses. They are hyper-adapted to living and foraging throughout the superstructure of woodland and forest, from the floor to the canopy. Even Tarzan couldn’t emulate the squirrels’ acrobatic feats up in the branches, and he’s fictional. Take the squirrels’ signature talent – the ability to run head first down trees. This is achieved by the hind feet rotating 180 degrees from a forward orientation. In other words, the feet move about the ankle to face backwards, with the claws digging into the trunk or branch. As a result, squirrels can manoeuvre as quickly down vertical trunks as up them.

Red squirrel climbing tree
Squirrels can rotate their hind feet 180 degrees, enabling them to descend treetrunks headfirst /Credit: Naturepl.com

Squirrel gymnastics are at their most impressive in the canopy. Who hasn’t delighted in the sight of one of these rodents leaping high from branch to branch or even tree to tree? 

Leaping is an important trick, saving a squirrel from bounding across the ground from one tree trunk to another, risking exposure to predators. The long, bushy tail can act like a rudder for last-second steering in mid-leap, and squirrels have whisker-like receptor hairs on their forefeet to help them sense the right landing. 

These adaptations are critical, because tree branches are rarely still. In autumn and winter, when the wind howls, the twiggy canopy must turn into an obstacle course of moving trapezes. 

grey squirrel in leaves
Unlike red squirrels, greys are able to digest acorns. Greys also have a superior memory , allowing them to recover their own caches - and steal those of the reds/Credit: Alamy

The squirrels’ thick fur is not just for keeping warm, either. A life of rushing about treetops is a prescription for bumps and bruises, so the fur protects them from brushes with thorns and twigs. Along with all this, squirrels have excellent vision to judge distances in three dimensions. 

A master of agility

Squirrels need all their agility and acute senses, because unfortunately they fit the profile of the perfect meal size for a host of predators. Having said that, the forests of Britain are somewhat denuded of larger mammals, and the suburbs are almost completely denuded of threats, so they are safer than elsewhere. Cats and dogs will sometimes catch them, and so will owls. In a few large forests, goshawks are a threat. But in the country as a whole, the most destructive ‘predator’ is probably the motor vehicle, which accounts for many thousands of deaths a year. Squirrels can cope with the complexities of treetops, but not the speed of traffic.

Red squirrel leaping
Squirrels have an impressive ability to leap large distances between branches and trees - a key survival tactic to avoid predators on the ground/Credit: Alamy

In recent years, another predator of squirrels has been shown to be significant, but with an intriguing twist. The pine marten, a bushy-tailed stoat-like hunter at home in the treetops, frequently has squirrels on its menu – but of a particular shade. In Ireland, at least, pine martens catch many more grey squirrels than reds. Red squirrels are smaller than grey squirrels and are significantly nimbler, spending much more time in the canopy and less on the ground than greys. The pine marten seems to find grey squirrels absurdly easy to catch. While the lighter red squirrel can retreat to the thin ends of conifer branches, out of reach, the grey squirrel is slower, heavier and more terrestrial. In places, the grey squirrel, introduced in Victorian times, seems to be a sitting duck – in Ireland, its range has retracted by 100km eastwards in 20 years as pine martens, legally protected, have expanded.

The Irish studies are the first light at the end of the tunnel for red squirrels for many a year. Since 1876, when the American grey squirrel was first foolishly introduced (as a nice change from the boring old red), it has capitalised on the misfortunes of the natives. Many people know that, in most of mainland Britain, the grey has ‘pushed out’ the red, but the ‘conflict’ between reds and greys is not black-and-white, and certainly doesn’t justify people dismissing greys as tree-rats and reds as adorable cuties. 

Grey squirrels don’t kill red squirrels. However, they tend to out-compete them in our deciduous woods and, crucially, they have a strong immunity to an infection, the squirrel pox virus, which wipes out red squirrels.
The virus visits in waves, and it is this that has put the red squirrel at such a disadvantage.
As the natives decline, the newcomers fill the gap and don’t relinquish it.

Wealth of memories

Grey squirrels have other advantages, too. It seems that they have a more accurate spatial sense and a longer-lasting memory. This is particularly important in the autumn, when squirrels cache food for their winter stores.

From September onwards, squirrels wake in the morning to find the trees bulging with fruit and nuts, more than enough for their daily needs. They can smell the abundance on the wind – indeed, they have been proven to smell ripe seeds on a tree from 400m away. So, having fed well from seeds in the canopy or on the ground, squirrels hoard the excess, often burying them under leaf-litter. They may store many hundreds of seeds and fruits in dozens of hiding places for retrieval in times of difficulty – squirrels have been known to dig through a metre of snow to reach one of their caches, using smell and spatial memory.

Within a wood, every squirrel is secreting food away, and pilfering is common whenever an individual wants easy food. Some animals take steps to avoid this, by pretending to bury phantom food when they know they are being watched. However, it seems that, with their enhanced memories, grey squirrels are inveterate robbers of red squirrel caches.

The two species have very similar diets, even though reds are mainly confined to conifer woods these days. Apart from seeds, squirrels eat a wide variety of vegetarian items, such as catkins, flowers and buds. Red squirrels have the unusual habit of eating large amounts of fungi in autumn, some of which they store to dry.

Chills and thrills

A curious quirk of squirrel behaviour is that both species breed in the middle of winter. So while we shiver, the squirrels are hot. This actually makes sense, because the autumn plenty enables squirrels to get into top condition, and when the young are born, in March, there are many buds and catkins around. Thus, one of the joys of wildlife-watching in late December and January is to watch the squirrels performing what look like exhausting mating chases. 

These are gruelling, and they are meant to be. The race involves a female being pursued by a number of males, often for hours on end. The chase goes up, down and around the tree trunks, stretching the animals’ athletic abilities and, above all, stamina. It is a slight exaggeration to say that the winner is the last male standing, particularly since both males and females will mate with several members of the opposite sex if they can, but at least it rules out the less healthy or uninterested individuals at the time.

Young red squirrels
Young red squirrels in a drey - a nest in the tree with a soft grassy lining. An average litter has three squirrels/Credit: Dk Images

The young (from one to seven) are born from February to April, into a covered nest called a drey. It is sited up in the crown, near the trunk of a tree. Thus, the youngsters begin their lives in the high places, where they will ply their trade as the ultimate artistes of the canopy.  

How to tell the difference between red and grey squirrels

RED

Red squirrel ID guide
Smaller yet lighter on their feet - the red squirrel/Credit: Alamy

• Smaller 

• Slimmer

• Typically chestnut-reddish coat, the colour not obviously patchy

• Neatly contrasting white belly

• Its ears are very obviously tufted (in winter)

• In summer, its tail often bleaches almost white

For more on the red squirrel, here are 25 fascinating facts

GREY

Grey squirrel
Heavier with a better memory - the grey squirrel/Credit: Alamy

• The grey is heavier-looking and not as light on its feet

• It never shows ear-tufts

• Its fur is greyish, sometimes with reddish patches but
never uniformly reddish

• Grey fur has grizzled appearance

• Its tail is edged with white

 

 

Main image: Naturepl.com

 

Dominic Couzens is an author and naturalist. His books include Britain’s Mammals (Princetown, £17.95) and Songs of Love and War: the Dark Heart of Bird Behaviour (Bloomsbury, £16.99)

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