A touch of frost in some Highland glens during the past few days will surely have sent a clear message to all creatures great and small that autumn has arrived. Decision time is approaching for many of our migratory birds although already, there has been some traffic in the departure lounge with many migrant birds now well on their way to warmer climes. For instance, I suspect that most osprey parents will by now have packed their bags and gone! The rooftops are silent too, the swifts, long gone a good few weeks ago.
Our birds and animals use many diverse ways of facing the forthcoming winter. Migrant birds, most of them insect eaters, of course don't take on that challenge. Instead they choose the different option of taking their leave of us and head south to spend their winters in the insect rich environment of Africa. Such journeys are of course, by no means a walk in the park. Indeed they represent a massive challenge in themselves. The miracle that is migration is still an amazing phenomenon when you consider the distances these intrepid travellers will attempt to fly, many of them taking on this great adventure for the first time. Furthermore, it is worth remembering that many of them weigh in at literally no more than an ounce or two. Most are minuscule yet will attempt to fly thousands of miles.
The challenges of migration are met in part by the fact that most of these adult voyagers will have renewed their plumage during late summer and so in that respect are in prime condition. Therefore, they look forward in the knowledge that the responsibility of rearing new generations is behind them, enabling them to concentrate solely on the job of getting themselves into the best bodily condition possible. Whereas earlier in the summer, all their energies were concentrated on the raising of families, during these early autumn days they now have time to look after their own welfare and plan for the big exodus.
The key before they embark on their journey is to be well fuelled up. Thus they will seek to increase their body weight by taking on extra food prior to departure. Body fat is the fuel that will sustain them and it is equally vital that as they make their way south, that they should keep on re-fuelling. Therefore, throughout their journeys they must always seek out food sources in order to keep their fat levels as high as possible. If that is not enough, they also face major physical hazards, which may see these birds crossing towering mountain ranges, featureless stretches of sea and for many of them, the immense Sahara Desert. And of course, they may encounter hostile weather conditions to boot, not to mention a host of predators finely tuned to taking advantage of their passage.
Intuition will play its part. Our own natural awareness of the weather conditions that are to come are dulled by the comfort zones in which we live. We travel in air-conditioned or heated vehicles, live behind double and even triple glazing and thus are not as exposed to coping with constantly changing conditions as for instance, our forebears were. Our wild creatures are much more attuned to variations in weather ... because they have to be!
Of course, the option of migration is denied to our mammals. The island nature of Britain precludes this approach. For example, in large land masses such as Africa and the Americas, these options are entirely viable as witness the immense movements of wildebeest across the plains of Africa and the equally dramatic movement across North America of the likes of musk ox. Thus, our mammals approach winter in different ways. Hedgehogs and bats choose to tackle the onset of winter by first feasting avariciously and then entering a deep sleep, better known as hibernation.
The pre-hibernation feasting is particularly vital for hedgehogs. Both bats and hedgehogs slow down their metabolisms markedly as they sleep in order to conserve energy, their breathing rates and pulses dropping until they are only just perceptible. However, for hedgehogs it is vital that their feasting is such that they can accumulate lots of body fat of which there are two distinct kinds - brown and white - both of which are equally important.
In the lower temperatures of winter, the brown fat mostly accumulated around the shoulders and the neck and chest is gradually absorbed by the slowly ticking metabolism of the animal. However, if temperatures fall suddenly, threatening to freeze the creature's blood, the brown fat automatically provides an instant and life-saving source of body heat. Contrary to popular opinion, hedgehogs do not sleep continuously through the winter. Warm spells can cause them to wake up from time to time and it is then that their survival is even more dependent upon that brown fat, for there is usually not enough food around to sustain them.
The white fat accumulates under the skin and around the body organs. It is not as full of energy as the brown fat but it serves, in particular, to protect the vital organs. Waking during the heart of winter is not a good idea and I well remember coming across a hedgehog scuttling along frantically in a roadside gutter one January day. For its own good, I caught it, took it home and offered it some tinned dog food, which it scoffed as if there was no tomorrow. I ensconced it in a well insulated cardboard box in the coldest room in the house, the utility room, where it stayed until spring, sleeping most of the time but waking occasionally to consume more dog food!
Other mammals also employ the tactic of accumulating body fat, not so that they can hibernate but to sustain them during the winter period when food is harder to find. Badgers do not hibernate. I have frequently found badger tracks in the snow and they do put on the 'beef' in the form of body fat during the autumn months. Thus when winter descends and produces spells of severe weather, badgers will happily sleep through the worst days relying on that fat to sustain them.
Meanwhile, just as the grain harvest is coming in rather fitfully due to the vagaries of the weather, another harvest will be gathered. Squirrels are renowned for the collection of nuts and beech-mast during the autumn months. Indeed, their endeavours in this respect could justifiably lead to an accusation of collector-mania, for they seek out and bury huge caches of such material, far more than they need for themselves when food is otherwise scarce or locked up by severe frosts. Of course, there are always thieves eager to deplete these stores and small mammals such as mice, voles and rats may well seize the opportunity to exploit these 'secret' stores in the drive for their own survival!
Therefore, during these next few critical weeks, there will be much collecting and much secret stashing on the part of our happily growing population of red squirrels and of course, on the part of grey squirrels too where they still dominate. However, there is another, perhaps unexpected hoarder, which during forthcoming weeks, will also be burying stores for the winter. Surprisingly, the jay is one of the few avian creatures that ensures its winter survival in this way, accumulating vast stores of acorns.
Survival beyond those glorious autumn days is the ambition of all such creatures. Each has its very own approach to what each year is the biggest test they are likely to face. Others, such as foxes, pine marten, the raptors and the rest of the crow clan, will on the other hand, try to survive simply by their wits! But then that is how these versatile creatures survive at any time of the year!