Hibernating wildlife – dormancy as a winter survival strategy

An overwintering Peacock butterfly at Newhaven Fort tunnels

 

Hibernating wildlife – dormancy as a winter survival strategy

Did you know that the Dormouse is named after the French word meaning 'to sleep': dormir? It's one of quite a few British wildlife species which have adapted to winter by dodging it entirely.

We're halfway through the darkest time of year and have arrived at that brief moment of suspended animation, the Winter Solstice, when the days neither shorten nor lengthen. The world seems to be in a state of dormancy. For much of our wildlife the toughest time still lies ahead. Food is in short supply; life is full of challenges. Species that aren't able to migrate need to tough it out, but some species have adapted to conserve their energy by hibernating.

Much energy is saved by entering a state of torpor – the result of reducing heart rate, breathing, metabolism and body temperature. The depth of torpor varies between species and it is punctuated with periods of activity within their hibernaculum, a place of hibernation and relative safety, protected from the extremes of temperature, humidity and wind.

Hibernating animals still burn energy, but at a much reduced rate. They need to ensure their fat reserves will sustain them throughout the winter. Like migrating species, hibernating creatures feast on the autumn harvest in order to maximise their body fat before entering the hibernaculum.

Who hibernates?

Insects

Most butterflies spend the winter as eggs (ova), larvae or pupae, but some species hibernate as adults and emerge on warm winter days and at the start of spring as the day-length increases. These include the Brimstone and Red Admiral, which hibernate deep within vegetation, and the Peacock and Small Tortoiseshell, which seem to prefer structures such as unheated buildings or rabbit holes, providing the light, temperature, humidity and ventilation are stable. Rabbit warrens are excellent places to search for emerging butterflies on warm, sunny spring days.

Many moth species also hibernate as adults, including the stunning leaf-like Herald and the Bloxworth Snout, a recent UK colonist which is tolerant of the cold and usually only enters a light hibernation.

If you have ever noticed swarms of ladybirds in late-autumn around your windows and doors, these are likely to be the Harlequin Ladybird – an invasive Asian species released in Europe to control aphids. Hibernating around fenestration protects them from frosts and moisture.

Some fly species also hibernate and the one most commonly encountered is the Cluster Fly, a parasite of earthworms, which likes to hibernate in roofspaces and false ceilings.

Reptiles and Amphibians

All British reptiles and amphibians hibernate, although my pond often has active frogs around it deep into mild winters. Palmate newts overwinter in the damp ground beneath logs and stones, where they are protected from predators and frosts. Reptiles such as snakes and lizards choose dry hibernacula such as old burrows and compost heaps.

Mammals

The only geniune mammalian hibernators are hedgehogs, dormice and bats, but most other species including rodents and badgers become less active. Bats are often found in similar places to butterflies and moths. Hedgehogs make a hibernaculum from dead vegetation and emerge only to add extra insulation if the temperature drops too low. 

A hibernating Herald moth (Scoliopteryx libatrix)

Gardening for hibernating wildlife – how you can help wildlife in winter

Not tidying parts of your garden will help to provide space for hibernating wildlife amongst long grass and vegetation. Creating log-piles, a compost heap or making a bug hotel will help insects, amphibians, reptiles and mammals overwinter. Remember though to check bonfires before they are lit for hedgehogs and other species.

You might find a butterfly or moth inside your home which has been woken by the central heating. By holding them gently it is fine to place them in an outbuilding or in a hedge that can be safely exited when spring arrives.

The effects of climate change can confuse species, especially if warmer winter temperatures cause them to emerge before there are sufficient food or nectar sources to sustain them. This can be especially harmful to bees, which are among the earliest hibernators to emerge on warm winter days, when there are few or no natural nectar sources. Growing winter-flowering plants and shrubs can help them, as well as placing food out for birds and mammals.

Bloxworth Snout (Hypena obsitalis) moths only enter a light state of hbernation and are more tolerant of low temperatures than many other species

 

 

All photographs taken by Steven Teale in the Newhaven Fort tunnels in East Sussex.