Surviving the winter: Plants and animals

Whilst I struggle with winter, at least I have a warm and cosy flat and somewhere dry and comfy to snuggle up.  Plants and animals don’t have it so easy.  Over time they have adapted a number of different ways to cope with the harsh weather that winter brings.

There are four main strategies for coping with winter:

  1. Stay active, but adapt
  2. Hibernate
  3. Die, leaving offspring behind in a form that lets them survive
  4. Migrate

Before we look at the options, let’s consider the problems that plants and animals face in the UK.  Obviously it’s cold.  There are frosts and this is a really significant factor as most organisms are made up of a lot of water and frost can lead to their tissues freezing which leads to death.  Other problems include reduced food supply, shorter days can mean less time to find food, lack of light, shortage of water in a liquid form, after all, you can’t drink ice.

Plants and animals know when winter is approaching by sensing environmental cues such as lower temperatures and shorter days.  This knowledge means they can start preparing, for example by building up fat reserves, shedding leaves, hoarding food etc.

Stay active, but adapt

Some organisms continue to be active despite the challenging weather and are able to do this because over time they have adapted strategies to help them.  Growing thicker feathers or fur is one such adaptation; the house sparrow has 11.5% more feathers in winter than in summer.  Squirrels which hide away nuts for the winter are another example of adapting to the weather.

Social behaviours change.  Birds which are normally solitary or found in pairs form flocks for the winter.  This increases food efficiency, reduces heat loss and increases protection from predators.

In the plant world, we see evergreen plants toughing it out.  The main issue for them in the winter is lack of water.  Their needle shaped leaves reduce surface area and this reduces water loss.  They also have a waxy layer which further prevents water loss.  This means the tree retains water throughout the winter and thus are better able to survive.  A lot of adaptations however mean trade offs.  In this case, the shape of the needles makes them less efficient in the spring and summer.

Deciduous trees also struggle with reduced water over winter and it’s also harder to photosynthesise when there is less light.  They’ve dealt with this issue by letting go of their leaves.  Before they do so, they move the water, sugars, minerals etc from the leaves to the woody part of the tree.  Then the chlorophyll in the leaves is broken down and reabsorbed into the main tree.  This leaves behind other pigments which aren’t useful to the tree such as orange carotenes and yellow xanthophylls which is why leaves become the gorgeous colours we associate with autumn.

Hibernation

Some animals will go into a full state of hibernation whilst others go into a sort of semi-hibernation which is affected by weather conditions.

In hibernation, the metabolic activity reduces significantly which helps them to conserve energy and survive the winter.  This includes incredibly low heart rates, as low as 10% of their normal heart rate.

Before hibernation, these animals must eat a lot of food and store it as fat.  Whilst this strategy allows animals to survive the difficult winter, it is imperative that they find food again soon after emerging.

Hedgehogs are one example of a true hibernator.  Depending on the weather, they may enter hibernation any time between October and December and emerge again in March or April.  During this period, their heartbeat can fall from 190 beats per minute to 20 beats per minute and its body temperature drops from 35˚C to just 10˚C.

Other UK hibernators include bats, dormice, some insects such as ladybirds, amphibians and reptiles.

Die

This might sound a drastic solution to facing winter but it’s one a number of species implement.  For example, annual plants will complete their life cycle in a year.  During the summer they release their seeds and then they start to die, but leaving behind lots of babies in the form of seeds.  Seeds are a much better form to face the winter in than as a leafy, lush plant which will not be able to cope with frost.

Another organism which often uses this strategy is butterflies.  Many butterflies die shortly after mating and laying eggs and their young then face winter as caterpillars and chrysalises which is much safer.  Some butterflies have adapted to hibernate over winter instead.

Migrate

About 40% of the birds that breed in Britain don’t spend winter here, instead heading off for sunnier places.  But it’s not just birds that migrate, caribou, reindeer, monarch butterflies and other insects all do as well (obviously not UK examples!).

Migration allows animals to find warmer places with better food supplies and less risk of freezing to death.  However, it’s not an easy option.  It’s estimated that swallows suffer 67% annual mortality, much of which is during migration.  Migration is an expensive venture in terms of calories and brings with it risks of predators, shooters and ….

Whilst you might not think it, more northerly birds do migrate to the UK for our comparatively warmer winters.  This includes many kinds of ducks and geese as well as fieldfares, redwings and bramblings.

Migrant butterflies include red admirals and painted ladies which arrive in vast numbers so their caterpillars can hatch here and enjoy the thistles and nettles in the summer.

A likely overlooked migrant is the basking shark which heads to our shores over the summer to eat the concentrated numbers of plankton found here.

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