Britain's birds suffer bust and boom due to 2011's roller-coaster weather
This year's freakish weather has seen Britain's bird populations go from bust to boom, with numbers recovering strongly from a disastrous collapse last winter.
It has been a year of freakish weather – from a blisteringly cold winter, to a sizzling, early spring and cool summer, not to mention an unseasonably warm autumn.
Now, new data reveals the extraordinary "roller-coaster" effect this has had on Britain's bird populations, with numbers hitting record lows before recovering at equally unprecedented rates.
Freezing temperatures at the start of 2011 left many species down to their lowest numbers for more than 20 years, and for some their worst on record.
However, the same species then capitalised on the early, hot spring to bounce back strongly, with some having their most productive ever breeding seasons.
The British Trust for Ornithology has released the preliminary results of two major monitoring surveys which track the fortunes of the UK's bird populations.
They lay bare the devastating impact that last winter's big freeze – the second coldest for a quarter of a century – had on many species as they found food, such as insects, snails and slugs, hard to come by and died off in large numbers.
The populations of dunnock, song thrush and reed bunting fell to their lowest on record, their populations having fallen by 21 per cent, 28 per cent and 23 per cent respectively compared with averages for the last five years.
Numbers of wren (down 31 per cent), robin (down 30 per cent) and chaffinch (down 15 per cent) reached their lowest ebb for 20 years.
However, in every case, the species took advantage of the extremely early onset of spring to produce record numbers of offspring.
For the dunnock and chaffinch, this was the most productive breeding season ever and for the song thrush, wren and robin, the best since the 1980s.
In total, of the 17 most common songbird species which spend the winter in the UK, 10 saw their numbers fall in the winter – and all but one then enjoyed above average breeding seasons.
As well as the warm weather, these species also benefited from the absence of competition for food sources.
Other species to thrive from the spring onwards were the kestrel, barn owl and tawny owl, which all recorded larger than normal brood sizes.
All three birds feed on small mammals like mice and voles – numbers of which were very high this year, after winter provided a blanket of snow to hide them from predators.
This allowed numbers to build up before the spring, when warm, dry weather created perfect hunting conditions for the birds.
The kestrel saw a 15 per cent increase in the number of fledglings produced per nest, making it their most productive season in 20 years, and encouraging for a population that has been experiencing an alarming decline in numbers.
For the barn owl, too, it was a reversal of fortunes, after its brood sizes in 2010 fell to one of the lowest levels on record.
Paul Stancliffe, from the British Trust for Ornithology, said: "It really has been quite a roller-coaster year for these species, having been hit so hard in the winter, but bouncing back strongly later.
"It just so happens we had really good weather during the spring and early summer, meaning some have had incredible breeding seasons.
"Had we had another cold, wet summer – like some of those we have had recently – the picture would have looked a lot worse."
Following a mild February and March, April saw the country experience a heatwave, with the hottest Easter holiday on record.
Summer was chillier than normal – the coolest for 18 years – but without extremes in terms of temperature and rainfall which could have harmed the recovery. The mild autumn – the second warmest on record – will also have helped the young birds.
Migrant birds escaped the impact of the cold weather and returned to Britain in large numbers, suggesting favourable conditions in their African wintering grounds.
Numbers of blackcap (up 44 per cent) and chiffchaff (up 47 per cent) were their highest on record.
But by contrast, many migrants then experienced a very average breeding season once back in Britain, because by the time they returned, they had missed the early spring and only experienced the cool summer.
One of the surveys, which has been running since 1983, involves recording bird numbers at more than 130 "constant effort sites'' around Britain and Ireland, by setting up nets approximately 500ft long at the same time and place each year.
Birds caught in the nets are studied to check their age and condition, before being ringed and released. Around 70,000 birds are recorded each year.
The method allows experts to assess the productivity of each species – the proportion of juveniles in the population, which indicates the number of young birds each adult has raised.
This gives ornithologists a better understanding of the successes, or failures, of each population than can be achieved using other methods.
The other survey, the "Nest Record Scheme", involves monitoring of nests, to count the numbers of eggs and chicks. More than 35,000 nests are monitored each season. It covers 70 species, including many that are not covered by the CES study and has been going for 72 years.
Both projects run throughout the calendar year and the final results will only be known at the end of this month.
The “residents” that suffered through the winter but bounced back following the early spring:
Wren – 31 per cent DOWN in numbers on five year average; 42 per cent UP in breeding success
Dunnock – 21 per cent DOWN in numbers; 52 per cent UP in breeding
Robin – 30 per cent DOWN in numbers; 60 per cent UP in breeding
Blackbird – 7 per cent DOWN in numbers; 15 per cent UP in breeding
Song thrush – 28 per cent DOWN in numbers; 45 per cent UP in breeding
Chaffinch – 15 per cent DOWN in numbers; 56 per cent UP in breeding
Reed bunting – 23 per cent DOWN in numbers; 7 per cent UP in breeding
The migrants that missed the winter – but missed the early spring too:
Garden warbler – 16 per cent UP in numbers; 29 per cent DOWN in breeding
Lesser whitethroat – 12 per cent UP in numbers; 36 per cent DOWN in breeding
Willow warbler – 23 per cent UP in numbers; 22 per cent DOWN in breeding
Source: The Telegraph
By Jasper Copping