Mass "twitcher" survey to record rare breeds starving in big freeze The cold weather is about to disappear, but its remnants may still turn this weekend's Big Garden Birdwatch, the RSPB's annual festival for amateur observers which is the biggest "citizen science" exercise in the world, into one of the most interesting ever, as the freeze has been forcing more uncommon birds into gardens in search of food. Waxwings, siskins, redpolls and fieldfares are among the less everyday species which may join house sparrows, starlings, blackbirds and blue tits in the gardens of many of the 600,000 or so people likely to take part today and tomorrow. "We're urging people to pay particular attention to their gardens and their feeders this weekend," said RSPB spokesman Graham Madge. A variety of quite unusual birds are coming into gardens from the countryside that are desperately short of food. Today the cold snap is expected to end with flooding replacing heavy snow as the major weather problem, especially in the south, as heavy rain moves in and rising temperatures spark a rapid thaw of the built-up snow. Temperatures will steadily increase from today before reaching more than 10C in the south tomorrow, followed by wet and windy weather next week. But in one last burst of cold, heavy snow was anticipated over northern areas last night, with a large part of Scotland, northern England and possibly the north Midlands expected to have more than 10cm (4in) of snow by this morning. Anyone can join in the Big Garden Birdwatch by spending one hour over the weekend, and noting the highest number of each bird species seen in their gardens or local park at any one time. Running for the last 34 years, it is the biggest wildlife survey in the world, and has made a major contribution to tracking garden bird numbers over the winter. The top 10 commonest birds in British gardens from the 2012 survey were, in order: house sparrow, starling, blue tit, blackbird, chaffinch, woodpigeon, goldfinch, great tit, robin and collard dove. But this weekend there is a real chance, Mr Madge said, of also spotting birds like the waxwing, a plump, crested, brownish and starling-sized songbird from Scandinavia, which this winter is visiting Britain in higher numbers than it has for 40 years. Similarly, he said, there is a chance of seeing striking and less common finches, such as siskins and redpolls, driven into gardens by the frost. A very likely possibility is another Scandinavian visitor, the fieldfare, a plump and colourful member of the thrush family, which has been seen in many gardens recently. More thrushes to watch out for include the fieldfare's Scandinavian cousin, the redwing, as well as the song thrush and mistle thrush - this last the subject of an alert from the RSPB, who warned this week that it is dropping seriously in numbers. Winging in: rare sights Waxwing (Bombycilla garrulus) A gaudy visitor from Scandinavia, above, sometimes arriving in large "irruptions" - as happened this year. Siskin (Carduelis spinus) A charming green, yellow and black finch whose normal home is the high tops of pine trees, now increasingly visiting gardens. Redpoll (Carduelis flammea) A streaked finch with a scarlet cap, a winter visitor from northern forests, but driven into gardens by hunger. Fieldfare (Turdus pilaris) A big thrush from Norway, now leaving the fields for bird tables in search of food. Mistle thrush (Turdus viscivorus) One of our two resident thrushes (the other being the song thrush), its numbers have dropped alarmingly.