Lots of questions about this subject crop up and this is no more than a rough outline.
Winter climatic conditions in the Northern Hemisphere vary enormously, and even when we take a relatively small land mass such as France, there are huge variations in the different regions. The reasons for this will be obvious to most people, and to put it very simply, they are the geographical differences between North, South, East, West, inland or coastal, mountains, and plains. Of course, it's actually more complicated, but we can all get the general idea.
For hundreds of thousands of years, creatures have adapted and specialised to survive these climatic conditions in different ways and hopefully will continue to do so, although many may find they struggle as climate chaos gathers pace and our demands on the environment increase.
Migration: Perhaps the most obvious method of dealing with winter is to physically move somewhere else, often long distances, mostly Africa, where it is warmer and where food is readily available in a suitable form. This is an absolute necessity for birds such as Swallows, Swifts, Bee Eaters and others that require a constant large source of flying insects to survive. It's equally as necessary for specialists such as Short-tailed Eagles that consume snakes and lizards. Then there are the other birds that travel from the North and North East of Europe to France, where conditions tend to be sufficiently milder and the ground in the West, South and South West is usually snow-free, allowing them to easily access nutrition.
Hibernation: This is a tricky one and not entirely straightforward. It is basically a period of dormancy or significantly reduced activity that is applied by different species of mammals and insects in a variety of ways. However, relatively few mammals actually go to sleep for the entire winter period, if at all. In France, the ones that do are Lérot (Edible dormouse). Loir (Garden dormouse) and Muscardin (Hazel dormouse). These are the three types of dormouse to be found in France. The Marmot, (an introduced species), also has a long hibernation deep in their tunnels in the Pyrenees. In addition, all the French bat species hibernate, and that usually, but not always, requires migration to their hibernation sites, which can be anything up to 100km or more from where they spend the summer. Hedgehogs normally hibernate for much shorter lengths of time, often waking up for periods of activity when the weather is mild and, in some cases, remain active for the entire winter period if it isn't too cold.
Full hibernation is only suitable for creatures that have adapted to going long periods (up to 6 months) without eating. For mammals, this means a period of fattening up beforehand and a metabolism that can almost cease for the entire duration. During hibernation, essential life functions for mammals slow down to a minimum, with a much-reduced heartbeat and breathing.
Diapause: Insects can spend winter as adults, larvae, or some intermediate stage of their development. Diapause is a state of suspended development or growth that occurs in response to unfavourable conditions such as extreme temperatures or limited resources. This will necessitate locating themselves somewhere where they won't freeze, such as in buildings, caves, inside dead or living wood, in woodland ground debris, and so on. It's different from hibernation, but some insects do actually hibernate.
Fox moth caterpillars hibernate in ground debris.
Brumation is similar to Hibernation except that it applies to reptiles and amphibians, which are cold-blooded creatures that depend entirely on outside temperatures to provide them with the heat they require. In brumation, both reptiles and amphibians are in a state of deep sleep, although they may still need to move to get some water and food to stay alive during this time; their activity is minimal. When in this state, and due to their ability to absorb oxygen in small amounts through their thin skin, some of our frogs can happily spend several months underwater in winter or buried in mud.
Chris
