A cold snap is a survival test

By January, a blue tit may weigh barely ten grams. Every one of those grams matters. A long night at minus five burns through a bird's fat reserves, and small species such as wrens, goldcrests and long-tailed tits must feed almost continuously during the few hours of daylight they have. Your garden, however small, can tip the balance between a bird making it through to spring and not. Three things decide the outcome: rich food, liquid water and somewhere warm to roost.

Feed for fat and calories

Winter feeding is about energy density. Seeds and nuts are good; fats and oils are better, because they deliver the most calories per gram. Stock up on suet balls, suet pellets and fat cakes, and offer them in wire feeders or on a hanging table rather than in the loose green netting some come in — the mesh can snag claws and tongues. Sunflower hearts are the best all-round seed: no husk to shell, high in oil, and eaten by almost everything from coal tits to greenfinches.

• Fat — suet products of all kinds, plus small amounts of mild grated cheese for robins and dunnocks.
• Seeds — sunflower hearts, nyjer for goldfinches and siskins, black sunflower for tits and nuthatches.
• Protein — mealworms, live or dried and soaked first so they do not swell inside a bird, for robins and wrens.
• Fruit — halved apples, pears and windfalls for blackbirds, song thrushes, redwings and fieldfares.
• Soaked raisins — rinsed and offered in a shallow dish; keep them well away from dogs, as raisins are toxic to them.

Skip bread, milk, salted or roasted nuts and leftover cooking fat. They offer little usable energy and can do real harm.

Feed little and often, and keep it clean

Put food out first thing and again in the late afternoon so birds can top up before the long night. In a hard frost, check twice a day — a feeder that runs empty mid-morning may not be revisited until dusk. Hygiene matters more in winter than many people realise: wet, crowded feeders spread trichomonosis, which has hit greenfinches and chaffinches hard in recent years. Wash feeders every fortnight in hot soapy water, rinse thoroughly, let them dry before refilling, and rotate their positions so droppings and discarded husks do not build up in one spot.

Water: the forgotten lifeline

Birds need to drink and bathe all year, but natural water is locked away the moment temperatures drop. A shallow bird bath with gently sloping sides is ideal; add a couple of clean stones or a small ramp so birds can wade in safely. Check it every morning and crack the ice — always by pouring a jug of warm, not boiling, water over it. Never add salt, glycerine or antifreeze, all of which are toxic. Floating a small ball in the water can help keep a patch open. Site the bath within a metre or two of dense cover so birds can retreat quickly, and give it a scrub once a week.

Shelter: dense cover saves lives

Roosting is where British gardens are quietly superb. Wrens often huddle in communal roosts of a dozen or more birds, and nothing beats a thick patch of ivy on a wall, a mature holly, a yew hedge or an overgrown pyracantha. Evergreens keep the worst of the weather off while screening birds from cats and sparrowhawks. If you have space, plant a mixed native hedge with hawthorn, blackthorn and holly, and leave it unclipped until the very end of winter so the berries last as long as possible.

• Leave ivy, teasels and seedheads standing — they shelter insects, which are food in themselves.
• Build a log pile in a quiet corner and allow fallen leaves to stay beneath the shrubs.
• Hang a roost box with a 32mm entrance facing north-east, away from the prevailing wet winds.
• Put two or three boxes close together; small birds huddle for warmth.
• Keep cats indoors at dawn and dusk, and place feeders where birds have a clear line of sight.

A few final jobs for the coldest weeks

Keep a spare bag of sunflower hearts indoors so a frozen morning never catches you out. Scatter a handful of coarse grit or crushed eggshell on a tray to help birds grind their food. Leave the garden a little untidy until March, and resist the urge to cut anything back hard. Then simply enjoy it: hard weather brings bramblings, siskins and the occasional waxwing into gardens, and a well-provisioned patch becomes the best birdwatching you will get all year.