Experts fear count will reveal a deadly winter for birds

Big Garden Birdwatch likely to expose extent of cold-weather cull of small species

It’s been the hardest winter for 30 years – but how bad has it really been for wildlife, and especially for birds? The first large-scale attempt to find out will take place this weekend, when half a million people will be counting the birds on their bird tables, patios and frozen lawns, in the Big Garden Birdwatch of the Royal Society for the Protection of Birds.

The annual survey, which is now the largest “citizen science” exercise anywhere in the world – last year more than 550,000 people took part – has a special relevance this year in the wake of the recent spell of extremely cold and hard weather.

The results are likely to give the first true indication of the scale of winter mortality among the commoner songbirds which visit gardens, particularly the very small species which are especially vulnerable to cold, such as long-tailed tits and wrens, and perhaps robins, .

People taking part in this weekend’s count simply watch their gardens for an hour, and record the highest numbers of each bird species seen at any one time; the pooled results give a clear snapshot of population ups and downs.

Last year, just under 552,000 people took part in the survey – a record number – counting over 8.5 million birds, with a total of 73 species recorded in 279,000 gardens across the UK. It showed the house sparrow retaining its top spot for the sixth year running, with an average of 3.70 seen per garden, while the starling, a former number one, came second with an average of 3.21 per garden and the blackbird was third with 2.84 per garden.

The big surprise of last year was the long-tailed tit, which, after a long run of very mild winters and a consequent population boom, entered the garden birdwatch top 10 for the first time. The “bumbarrel”, as it was once affectionately known, was the 10th-commonest bird seen in gardens across Britain in 2009, with almost double the previous number recorded.

However, this is one of the species where a winter decline is expected, as it is so small (the tail is longer than the body) that it is very vulnerable to the cold, and in really harsh weather as many as 80 per cent of the population may die.

“It’s unlikely the long-tailed tit, which famously flew into 10th place in 2009, will remain in the top 10 this year,” said Dr Mark Avery, the RSPB’s Director of Conservation.

“Sadly, we may even see the nation’s favourite garden bird, the robin, also fall out of the top 10 in 2010. If this is the case, it will be the first time the robin hasn’t featured in the top 10 since the start of the survey.”

In wildlife terms, this winter is already being compared with the famous winter of 1962-63, when the freeze began on Boxing Day, gripped all of Britain, and did not begin to thaw until the first week of March. It was estimated that half the birds of Britain died in the cold; the Dartford warbler population was slashed by 98 per cent, wrens by nearly 80 per cent and over much of the country, kingfishers were extirpated.

Although 2010 has not so far provided such an unremitting freeze, the lengthy period of snow and ice earlier this month is thought likely to have been fatal for much wildlife, |and to have driven other birds into gardens, where they would not normally be seen.

“We can expect to see some more unusual visitors to gardens, particularly redwings, fieldfares and tree sparrows that are struggling to find food elsewhere, Dr Avery said.

The top 10 garden birds last year were (in order): house sparrow, starling, blackbird, blue tit, chaffinch, wood pigeon, collared dove, great tit, robin and long-tailed tit. Although remaining at the top of the list, both the house sparrow and starling have suffered huge declines since the survey began 30 years ago, the former going down by 63 per cent, and the starling by 79 per cent. Ten sparrows were seen per garden in 1979, compared with 3.70 this year, while 15 starlings were seen in gardens 30 years ago, compared with only 3.21 in 2009.

1963: the killer winter

It was greater in its effect than pesticides (and God knows that was bad enough), it was greater than shooting, or egg-collecting, or any human actions, or anything else that came along in the course of the 20th century: the winter of 1963 was the biggest calamity to hit the birds of Britain in modern times.

Right through January and February that year, snow covered the country continuously as a rare meteorological phenomenon, a “blocking anti-cyclone”, kept out warm winds from the west and south and maintained a steady and unrelieved stream of icy air from the north and east. The ground froze as hard as concrete, and so did the rivers and ponds, and so, even, did the edge of the sea.

It meant that food supplies were cut off completely from land birds and water birds both, and the calories drained away from them as they tried to maintain bodily warmth and energy without any fuel. As the smaller you are, the greater your body surface in relation to your volume, the smallest birds leaked heat the most, and they suffered proportionately.

Britain's smallest common garden bird, the wren, virtually vanished; about eight out of ten British wrens died. When summer 1963 eventually came, and the Nest Records Scheme of the British Trust for Ornithology recorded the breeding activity of wrens, it found there were only 23 per cent of the nests that were found in 1962.

The wrens that survived, researchers discovered, had sometimes done so by finding bizarre hiding places: burrowing into haystacks, or squeezing into rat holes.

The Dartford warbler, our only warbler species to take the risk of staying here for the winter (the other 13 all head for Africa) did even worse; there were 450 pairs when the winter began, and when it ended, there were 11; a mortality of about 98 per cent. The kingfisher, cut off from its sticklebacks and minnows by the ice, simply went extinct in many areas, especially across large swathes of eastern England. Numerous other bird species, from thrushes to herons, went down in numbers by half. If birds could talk, they’d be talking about it still.