Surviving Winter

For many of us, the dark days of winter can plunge us into melancholy and we long for the first signs of spring to brighten up our lives.  In the current Covid induced isolation it can be even harder to be positive but perhaps we can seek inspiration from observing the wildlife around us and see how marvellously they are able to cope.

Optimizing your winter strategy

In general, the ways animals and plants survive winter fall into three main categories:

1. leave and go to warmer climates
2. stay but become dormant
3. remain active and adapt. 

Naturally, within each of these key strategies there is a great diversity of approach that has been optimized by evolution over the millennia to enable our local creatures to cope with a cold (and wet) northern winter

Plants have limited options.

For most plants the only option is to become dormant as the winter frosts will damage growing tissues.  Annual plants can pass the winter as seeds waiting for the warm weather and lengthening days to stimulate germination.  Perennial plants tend to die down to the ground with nutrients stored in their roots protected under the soil.  Some plants have specialized bulbous roots or stem bases to store nutrients for a quick start after the worst of the winter weather is over.  Most of our native trees and shrubs extract nutrients from their leaves and shed them at the end of autumn; storing the precious nutrients in their trunks and roots ready for the spring.  Notable exceptions are the so-called evergreens like Holly and Ivy as well as coniferous trees.  The main issue for plants that keep their leaves during winter is that the low temperatures prevent the roots from taking up water and replacing what is lost through the huge surface area of the leaves.  Most conifers have needle-like leaves to reduce surface area relative to volume but to further prevent damaging desiccation, the mature leaves have thick waxy cuticles which together with stomata (pores for gas exchange) located in the base of deep pits, reduces passive water loss.  The downside of this approach is that the leaves are not as efficient in the normal growing season.

Insect mobility offers more ways to survive

Most insects are also dormant during the winter months but some appear to be able to migrate considerable distances to warmer climates.  Good examples include the Monarch butterfly, a North American species which has well documented migrations, in which the eastern population spends the summer in the USA and Canada and, after breeding, fly south again, mainly to a small area of Mexico.  Until recently it was thought that butterfly migration in the UK was just in one direction as a result of population explosions in North Africa and Europe.  However recent research in the UK, where movements of Painted Lady butterflies were followed using radar and ground observers, has shown that they do in fact fly south again, to Africa in the autumn, on one of the longest known insect migrations.  This had been previously been overlooked as they flew south at relatively high altitude (over 500 metres above the ground) and at speeds up to 30 mph.

Insects, their larvae and other invertebrates that live underground, underwater or deep inside wood can continue to feed throughout most of the winter protected from the worst of the cold by an insulating layer of soil, water or wood.  However, for most insects their food sources are not available in winter so they become dormant in one of their life cycle stages.  Interestingly it is often the case that within the same group of insects, different species will spend the winter at different stages.  For example, in our native butterflies, Small Tortoiseshells and Peacocks will spend the winter as the adult butterfly, Purple and White-letter Hairstreaks will spend the winter as an egg, Pearl-bordered Fritillaries and Meadow Browns (as well as most of the other meadow butterflies) will spend the winter as small larvae, and Orange tips and Green-veined Whites will spend the winter as pupae.  The impact of these different approaches enables butterflies and other insects to exploit different habitat niches as well as reproduction strategies.

Birds are the masters of migration

The ability of birds to fly has enabled them to exploit a range of breeding habitats that would have far too little food to support them in winter.  This has led to some amazing annual migrations and contributes to the diversity of birds that we see in our countryside.  As well as the familiar Swallows and warblers that visit our gardens each summer, we also have a good numbers of winter visitors such as Redwings and Fieldfares.  Many birds also adapt their behaviour and utilize different food sources to keep themselves alive in the cold weather as well as cashing food when it is abundant to be eaten later.  They are also more likely to gather up into flocks which can both help to protect them from predators but also conserve energy in winter roosts.  Who can fail to be amazed by the sight of a Starling murmuration, but the benefit to the birds is that by roosting close together they keep each other warm.  Some birds also have specific winter plumage that is more insulating and in the House Sparrow, it has been shown that they have over 10% more feathers in winter.

Mammals are good at staying active in winter

Many of our mammals remain active during cold spells.  I am always amazed when a covering of snow melts on our meadow and the runs of the Field Voles are revealed.  The snow had insulated them from the worst of the cold and protected them from aerial predators allowing them feed unmolested above ground on the grass.  One notable exception to keeping active is the Dormouse.  A master of hibernation which reportedly can sleep for up to seven months a year! It is increasingly scarce due to habitat loss but the Trust is working hard to support populations at several of its reserves.  Another exception are bats.  We are lucky to have a Lesser Horseshoe Bat that uses one of our outbuildings as a summer roost but in November, it leaves us to go to its winter roost which we suspect is in the old mines at Roundton Hill nature reserve.

Our local wildlife is well adapted to our winters

We should not be too surprised how well adapted our wildlife is to winters, especially when you think only 12,000 years ago, much of the UK was covered in a deep ice sheet up to 600m thick.  Most of Montgomeryshire would have been covered in snow and ice for much of the previous 50,000 years with only the tops of the Cambrian mountains exposed and providing places for a few lichens and mosses to grow.  It is thought that the Snowdon Lily is one of the few plants found in Wales that has survived as a relic from this glacial age.  As the temperatures rose, plants and animals from further south began to colonize what was initially something close to arctic tundra.  As the warming became more rapid, scrub and trees began to invade too.  Over the intervening years the temperatures fluctuated but eventually became generally warmer and closer to what we experience today.  The reason that our animals and plants were able to move into the habitats created by the receding ice at the end of the last ice age is that they are extremely well adapted to finding and exploiting the changing habitat niches created by gradual temperature change.  The reality is that the plants and animals that we have in our countryside today are well adapted to cope with the natural annual temperature fluctuations we experience through the year as well as the changes from year to year.  It remains to be seen how they respond to the man-made changes in climate that we are experiencing today.

So, should we be supporting our local wildlife in winter?

In a truly wild environment, without the dramatic impact humans have had upon it, my answer would definitely be “No”.  However, in our imperfect world with all the pressures on the countryside, from development and intensification of agriculture, giving a helping hand to nature may assist in reversing the declines we are observing in many of our native species.  The RSPB have shown that winter feeding of birds in urban areas significantly increases their winter survival.  It is also a great opportunity to get a closer look at some of our most engaging wildlife at a time of year when it is more difficult to spend time outside.  Similarly, having plants in our gardens with winter berries and leaving some fallen apples is a great way to help the overwintering thrushes.  Finally, making sure that there are places for wildlife to shelter in our gardens is also important.  This can be as simple as leaving bits of the garden ‘untidy’ together with a few piles of cut branches, as well as providing more purpose-built shelters if you can.

I hope that this blog will encourage you to look more closely at our wonderful winter wildlife and enable you to find a pleasing and uplifting distraction from the grey winter weather and difficult times that we are all facing at the moment

Tim

Disclaimer

Any views or opinions represented in this blog are personal and belong solely to the author and do not represent those of people, institutions or organizations that the author may or may not be associated with in professional or personal capacity, unless explicitly stated