Winter Science

Tetrapods: The Four Survival Strategies

To survive the British winter, mammals, birds, reptiles, and amphibians (tetrapods) utilize four primary physiological and behavioral tactics.

1. The Sleepers (Hibernation & Brumation)

Only a tiny "elite" group of British mammals truly hibernate by effectively "turning off" their bodies.

• True Hibernators: Hedgehogs, dormice, and all bat species. A hedgehog's heart rate can drop from 190 bpm to just 20 bpm to save energy.

• Brumation: Cold-blooded reptiles and amphibians, like the Common Lizard, enter brumation. They can increase glucose in their blood to act as a natural anti-freeze, surviving temperatures as low as -3.5°C.

• Skin Breathing: Common frogs may hibernate at the bottom of ponds, absorbing oxygen from the water through their skin.

2. The Active Survivors (Adaptation & Torpor)

Many species remain active but change their physical "settings".

• Dehnel's Phenomenon: Common shrews actually shrink their skeletons, skulls, and brains by up to 20% to reduce the food needed to stay alive.

• Torpor: Badgers and squirrels use short-term "emergency" naps that last only a day or two during severe weather.

• Insulation: Foxes, deer, and otters grow dense, oily undercoats. An Otter's fur is 200 times denser than human hair, making it completely waterproof.

3. The Shifters (Migration)

• International: Swallows and swifts fly thousands of miles to Africa to find insects.

• Altitudinal: Birds like Meadow Pipits move from frozen uplands down to the milder coastal marshes of Devon.

• Arctic Refugees: For birds like Turnstones, the Sidmouth winter is "warm" compared to the Arctic, so they migrate here.

4. Irruptions (The Unplanned Move)

An "irruption" is a dramatic, unplanned movement of huge numbers of birds, often following a food source failure in Scandinavia.

• Common Irruptors: Waxwings and crossbills.

• Winter Destinations: While we think of Blackcaps as summer visitors, ringing data shows that some individuals seen in Sidmouth in winter have actually nested much further north.

• The Beak Clue: In winter, blackbirds with yellow beaks are usually local, while those with orange beaks have often travelled from mainland Europe.

Arthropods: Chemical Transformations

Insects and spiders face a unique challenge: being small and cold-blooded, they freeze quickly. To survive, they undergo total chemical transformations.

• Diapause: A programmed "biological pause button". Insects replace water in their blood with glycerol or sorbitol, lowering their freezing point so they remain "liquid" even below 0°C.

• The "Stage" Strategy: Species overwinter in their most "hardened" form: Adonis Blue as eggs, Stag Beetles as larvae in rotting logs, and Orange-tip Butterflies as pupae camouflaged as dead leaves.

• Huddling: Seven-spot ladybirds huddle in groups of hundreds in masonry or ivy to retain collective metabolic heat.

• Active Specialists: Winter gnats and spiders remain active because there are fewer predators. They possess proteins that prevent ice crystals from damaging their cells.