How long is it since you filled your bird feeder or replenished the water in your birdbath? If you haven't done it for a while, there's no time like the present.
"The sudden drop in temperatures across the UK will have been a big shock to birds' systems after spending the past couple of months with few worries in terms of food availability," says Richard James, RSPB wildlife adviser.
"Thanks to the recent mild weather, many natural food sources have been readily available and water has been easy to come by. Now the snow and ice are here birds will need all the help they can get to survive the winter."
However, the range of bird seeds, fat balls and other so-called bird-friendly items can leave gardeners baffled as to what's best for our feathered friends.
The RSPB suggests calorie-rich foods such as mixed seed, nyjer seed, fatballs, suet sprinkles, sunflower seed and good quality peanuts, as well as kitchen scraps such as mild grated cheese, rice and porridge oats.
There are different mixes for feeders and for bird tables and ground feeding. The better mixtures contain plenty of flaked maize, sunflower seeds, and peanut granules.
Small seeds, such as millet, attract mostly house sparrows, dunnocks, finches, reed buntings and collared doves, while flaked maize is taken readily by blackbirds.
Tits and greenfinches favour peanuts and sunflower seeds. Mixes that contain chunks or whole nuts are suitable for winter feeding only.
Pinhead oatmeal is excellent for many birds. Wheat and barley grains are often included in seed mixtures, but they are really only suitable for pigeons, doves and pheasants, which feed on the ground and rapidly increase in numbers, frequently deterring the smaller species.
Avoid seed mixtures that have split peas, beans, dried rice or lentils as again only the large species can eat them dry. These are added to some cheaper seed mixes to bulk them up. Any mixture containing green or pink lumps should also be avoided as these are dog biscuit, which can only be eaten when soaked.
Don't feed the birds cooked fat from roasting tins and dishes, because the fat may have blended with meat juices which leaves a mixture prone to smearing, which is not good for the birds' feathers, and is a breeding ground for bacteria, the charity warns.
Polyunsaturated margarines and vegetable oils are also unsuitable as birds need high levels of saturated fat to retain the high energy to keep warm, and soft fats can be smeared on to feathers, destroying the waterproofing qualities.
Lard and beef suet on their own are fine as they re-solidify after warming and are not as prone to bacteria breeding because they are pure fat.
Never give milk to the birds because it can result in serious stomach upsets or even death. They can, however, digest fermented dairy products such as mild grated cheese, which may attract robins, wrens and dunnocks.
If you want to give the birds coconut, only give them the fresh stuff in the shell, rinsing out any sweet coconut water before hanging it out, to stop black mildew emerging. Desiccated coconut should never be used as it can swell inside the bird, with fatal consequences.
Cooked rice without added salt can be beneficial to birds during severe winter weather, while uncooked porridge oats are fine for many bird species. You can also put out small quantities of dry breakfast cereal.
A supply of water is also essential for bathing and preening. In freezing conditions birds become more dependent on water provided in gardens, since many natural sources are frozen over.
The most effective way to keep the water in your garden from freezing is to pop in a light ball that will be moved by even a gentle breeze - a ping-pong ball is ideal.
Alternatively, pour on hot water to melt the ice to make sure the birds can get to it.
:: For more information, visit www.rspb.org.uk