Weekly Nature Watch

Weekly Nature Watch 16th October 2020

on .

We are entering that technicolour time of the year as autumn’s spell begins to coat the landscape in richer hews.

There are golden moments, red moments and rich brown ones, a fitting farewell to a year rapidly coming to its end with a flourish which this time around appears to me to be even more colourful than in previous years. Millions of birds have already departed these shores rather than face our winter when, for most of them, the insects upon which they rely for food have hibernated or become dormant. The birds that have left are already being replaced by others whose Arctic homes are fast becoming untenable as temperatures plummet and frost begins to bite harder by the day, persisting and locking up the ground upon which many of them feed. That our winter visitors have arrived is witnessed by the sounds of cackling geese which are beginning to pervade our landscape. This is the sound of winter.

In so many ways, it is changeover time as day by day the hours of daylight shorten and winter nears. This means that some creatures, unable to escape by transporting themselves those thousands of miles south, begin instead to prepare for the big sleep. They have developed a more unique way of fighting the winter - they simply sleep their way through it. Perhaps the most familiar of those that hibernate are our intrepid garden occupants, the hedgehogs. Yet the process is not as simple as once thought. It is not simply a case of finding a suitable place to bed down - a hibernaculum - falling resolutely asleep and expecting to re-awaken when rising temperatures signal a resumption of normal life as spring begins to make its influence felt. There is much preparation to undergo which entails cashing in big time on autumn’s bounty and eating as much as is possible.

There are several of our mammals which were thought to hibernate but which do not. Squirrels, for example, employ another interesting technique which involves the establishment of caches of food – again making the most of autumn’s bounty and saving and storing large reserves of food, carefully buried so that when winter really begins to bite and other food sources become scarce, they have enough to sustain themselves. Most squirrels are very wary of those colourful members of the crow family, jays, for they are eagle eyed in their ability to make a mental note of where for instance squirrels have hidden their reserves and are certainly not averse to a spot of thieving!

Nor do badgers hibernate. Brock also capitalises upon autumn’s bounty and will enter winter with a few surplus pounds to spare so that when the weather turns really hostile, he may decide to lie up for a few days and not venture beyond his snug underground sett, relying instead on the surplus fat that he has acquired in much the same way as hibernating animals store energy in their bodies.

A surprising number of small mammals establish similar stores to those of squirrels so that there are always plenty of candidates when it comes to raiding of other animals’ stores. But the key to successful hibernation depends upon the ability of creatures to build up stores of food and thus energy in the form of body fat in their bodies which will sustain them whilst they are asleep. The entire metabolism of a hibernating animal slows right down during the months of sleep, so much so that the heart and breathing rate will reduce to an almost imperceptible level. Thus, they are sustained by a constant drip, drip, of energy - just enough to ensure that the basic body functions can be kept functioning.

Therefore, from late summer onwards the hedgehog’s aim is to build up those body-fat reserves which can later be translated into vital energy when winter sets in. There are two types of fat built up in the hibernating hedgehog’s body, brown fat and white fat. The brown fat builds up around the shoulders, neck and chest and has a higher calorific value than the white fat. During exceptionally cold winter weather, a hibernating hedgehog’s blood can actually freeze, causing irreparable damage to the body’s organs.  In such conditions, the hedgehog is likely to wake and their immediate energy source is the brown fat. However, it may also be necessary for the waking animal to quickly find a better place to resume its sleeping mode because during the winter months, food is hard to find and it is important not to deplete the stores of fat unnecessarily.

The white fat is concentrated under the skin of the animal and around the vital organs. This fat is used during the early stages of hibernation and as said before, is marginally less nutritious. However, previous theories about hibernating animals bedding down in the autumn and sleeping solidly on until spring have been disproved. It is now thought that hibernating hedgehogs wake quite regularly. I certainly recall once coming across a young hedgehog scuttling along a roadside gutter on a January day. I rescued it, took it home and installed it in a hay filled box in the utility room together with a selection of tinned cat food. The hedgehog slept for most of the time but periodically woke to top up its food requirements.

Hedgehog numbers are these days much depleted and of course their normal defence of rolling up into a prickly ball is not effective against the modern motor vehicle. Hedgehogs are most active by night and they are not always easy to see when they cross roads.  The number of hedgehogs that perish on our busy roads is hard to ignore and I always feel especially sad in the springtime when hedgehogs emerge from their hibernation only to meet their fate under the wheels of a vehicle. It amounts to a winter spent sleeping in anticipation of forthcoming spring only for it to suddenly end.

In recent times, I have heard people blame the badger for the dearth of hedgehogs. Certainly, Brock is strong enough to easily overcome the hedgehog’s defences, however I have never yet found a dead hedgehog that I could definitely say had been killed by a badger. Hedgehogs and badgers have lived together for millennia so I think that it is highly unlikely that the badger could be having the effect of severely curtailing the lives of hedgehogs. The alternative suggestion I have heard is that wildcats too are able to penetrate the prickles of a hedgehog but as there are so few true wildcats remaining, I hardly think they would pose a problem.

The other creatures that enter a period of winter hibernation are of course bats and although I am no expert, I suspect that they also feast avidly on the insect life of autumn in order to build up energy reserves which will sustain them during their long sleep. Our reptiles too hibernate in order to avoid the winter and of course, further south in England, the dormouse is another creature that sleeps through the winter months.

These then are the various ways in which different species of animals, birds and reptiles survive our winters, either by leaving these shores altogether and seeking solace in warmer climes, by establishing stores of food to sustain themselves through the long months or by simply building up bodily reserves of fat which provides the energy that keeps them alive whilst they sleep. Winter is definitely a coming and so hopefully we won’t be seeing the likes of hedgehogs again until next spring.

Any natural place contains an infinite reservoir of information, and therefore the potential for inexhaustible new discoveries.

Richard Louv, Last Child in the Woods