A major wildlife survey has today confirmed the worst fears of birdwatchers: the coldest winter for 30 years was disastrous for small birds.

Sightings of small species such as the goldcrest, coal tit and long-tailed tit were dramatically down compared to after the previous year's mild winter, the RSPB's Big Garden Birdwatch found. The survey, which was conducted by over half a million people in January and is the world's largest public participation wildlife event , also showed a significant rise in hungry countryside birds such fieldfare and redwings visiting gardens in search of food.

Sarah Kelly, the survey's co-ordinator, said: "We were particularly concerned for small birds over the winter, asking people to make sure they kept feeders topped up and supplied with fresh water to help them. Smaller birds have to eat for more of their waking time as the temperature drops, and during hard frosts and snow cover often have to feed 100% of the time from dawn until dusk. Many smaller birds will be in trouble if they fail to find food even for a day."

The survey saw 530,000 people take part and their records showed the average number of birds per garden for already rare goldcrests were down 75% on January 2009, being seen in only about 5,300 gardens. Long-tailed tits were down 27% to an average of one bird per garden, and coal tits down 20%. The long-tailed tithad been thriving due to a succession of mild winters and was one of last year's big success stories.

This winter's bitter weather had a greater impact because the cold spell was national Kelly explained. Most previous drops in small bird populations caused by cold weather - such as the death of all the Cetti's warblers in Kent after two successive cold winters in the mid-1980s - were only regional.

The snowy winter also led to a huge rise in sightings of countryside birds such as thrushes and finches in the UK's gardens. The number of fieldfares was up 73% on last year, redwings up 185% and song thrushes up 51%, though their numbers are still relatively low compared to garden stalwarts such as blue tits and chaffinches.

Kelly said snow on the ground and frozen berries had led the rural birds to look further afield for food, venturing into gardens. Modern farming methods, where fields are no longer left to seed during winter, have also been cited as a cause by the British Trust for Ornithology.

Another species apparently doing well was the blackcap, which was up 47% against 2009 levels. The RSPB believes many may have been migrants sheltering from even harsher weather in mainland Europe, though it also speculates that the increased sightings may simply be a result of the blackcaps getting used to eating from bird feeders and becoming more visible.

However, the long-term picture painted by the survey is still one of a general decline in garden sightings of birds since its inception in 1979. House sparrows (the most-spotted bird) and starlings (down from number two to three for the first time in over 10 years) have seen numbers drop respectively 62% and 79% since the survey began. Aside from blackbirds moving up the list from third to second, the top ten list is otherwise similar to previous years, featuring wood pigeons, robins and great tits.

Garden birds were also assisted by an enthusiastic public response to conservationist's calls to put out feed. Two in three people in the UK feed garden birds and the rush to help birds through the cold spell also helped businesses such as the Garden Centre Group, which saw sales of wild bird feed rise 8% in the five weeks to the end of 2009.

The freezing weather has delayed breeding too, said Tim Harrison, development officer for the year-round garden birdwatch run by BTO: "On Valentine's Day 2010 there were nine species recorded as having active nests - ie eggs and/or young - compared with 16-17 species in milder winters."

The RSPB survey involved participants counting birds in their garden over one hour on the weekend of 30-31 January. Guardian readers submitted hundreds of photos of their sightings to a dedicated Flickr group and took part in a 'live' birdwatch on theguardian.com.

Ups and downs, compared to the 2009 survey

Blackbirds - up 16%, 3.28 birds per garden in 2010, up from 2.84 in 2009

Reed buntings - up 140%, 0.03 birds per garden

Song thrushes - up 51%, 0.37 birds per garden

Bullfinches - up 54%, 0.18 birds per garden

Robins - up 10%, 1.49 birds per garden

Goldcrests - down 75%, 0.01 birds per garden

Long-tailed tits - down 27%, 0.97 birds per garden

Coal tits - down 20%, 0.60 birds per garden

Siskins - down 31%, 0.09 birds per garden

Greenfinches - down 18%, 0.88 birds per garden

Tips to help birds survive the cold

• Put out a variety of feed - seeds, fatballs and peanuts

• Break ice, and leave out fresh water daily. Never put add anything, especially salt, as it can kill birds.

• Clear snow from lawns to help ground-feeding species such as blackbirds

• Create homes for birds with nestboxes, and preserve old trees that have holes