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 few 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 birds.

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.

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.

Never give birds milk 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.

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.

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.

Put out enough food and you may see a wider variety of visitors during the RSPB’s Big Garden Birdwatch this weekend, the world’s biggest wildlife survey.