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Nature blooms in mysterious ways during a British winter that thinks it's a spring

If one swallow makes a summer, how many make a winter? The bird that more than any other symbolises the life of the new growing season, is still to be seen across Britain, long after the old season has died.

If one swallow makes a summer, how many make a winter? The bird that more than any other symbolises the life of the new growing season, is still to be seen across Britain, long after the old season has died.

At Berwick-upon-Tweed on the Scottish border, in Yorkshire, and in East Anglia and Sussex, swallows have been sighted swooping at insects as if it were spring. They are only part of a remarkable response by the natural world to one of the warmest Decembers on record.

After the wettest-ever autumn, we now have a winter that thinks it's a spring. Britain's topsy-turvy weather is continuing with such high December temperatures, that some birds, flowers, insects and animals have been behaving as if it were April, rather than the run-up to Christmas.

While swallows and many other migrant birds should long ago have left for Africa, spring flowers are also bursting into bloom, butterflies are on the wing in the sunshine, bats are hunting for insects by moonlight, and frogs have started to lay their spawn.

The warmth has caused it. Although temperatures started to turn down late this week, it may have been the warmest first half of December on record. The average mean temperature over central England between December 1 and 13 was 9.1C, nearly double the normal mean of 4.9C.

The record for the month as a whole, in a list going back to 1659, is only 8.1C, set jointly in 1934 and 1974, so if December were to continue as it has begun, the record would be easily broken.

The warmth has come from southerly airstreams flowing over Britain from the sub-tropics, replacing the normal December airflow from polar latitudes. Two days ago, however, a more northerly airstream began and it is likely that the rest of the month will be not so mild.

The response of the natural world to the unseasonal warmth has already been phenomenal. Experienced birdwatchers have been astonished to see swallows this month, normally gathering on telephone wires by August, and well on their way to Africa by September; three were seen at Sizewell in Suffolk two days ago, while their cousins, house martins, have also been reluctant to leave East Anglia, with as many as 10 being counted, together, at Cromer.

Other birds, which hardly ever overwinter in Britain, have also been seen in the last week. They include a sand martin, a swift, a wheatear and a ring ouzel - the blackbird of the moorlands.

Other signs of spring include the sound of many birds singing loudly and often - when usually only sporadic bursts of song are heard in winter. Species such as blackbird, song thrush, mistle thrush and dunnock are in full song in many areas of Britain - and the watery winter song of the robin, the symbol of Christmas, has changed to summer boldness.

A consultant to the British Trust for Ornithology, Chris Mead, said that it is "remarkable" that such a wide range of summer visitors have been reported lately.

"This must be linked directly with the weather, which has been unusually mild for the time of year," he said. "Many are insect-eaters, and to survive in our winter, they need to be able to find enough food during the few hours of daylight to sustain them through the long nights. Obviously, they have been achieving this.

"However, a cold snap will inevitably catch out those who don't move south. This weekend's switch to more wintry weather could result in a significant reduction in these unseasonal reports."

The birds are still here, largely because the insects they feed on are still flying, and the more visible ones, such as butterflies, have been widely spotted. There have been many sightings of some of the most handsome butterflies, including red admirals - seen in London and right across southern England - peacocks - seen at several places in Cheshire - and small tortoiseshells. The southerly winds have also brought sightings of migratory species - notably five, painted lady butterflies - at St Austell, Cornwall. If the birds want insects, the insects want plants, and a number of wild and garden flowers, that would normally bloom only in the spring, are now well out. Rhododendrons are flowering in many places, as, in the south, are snowdrops - a month early - and also lesser celandines, a traditional sign of spring. Even red campion, which gives hedgerows much of their brightness from March onwards, is flowering as far north as County Durham. Still-flowering roses are wide-spread.

In the animal world, the first frog-spawn of next year has been sighted in Cornwall - found at a nature reserve on The Lizard peninsula on December 9 - one of the earliest sightings on record. Spawning would normally start in the south-west in late January. At the Wildfowl and Wetlands Trust Centre in Barnes, south-west London, they are still pond dipping, and finding freshwater shrimps, hog-lice and dragonfly nymphs. "That would have been unheard of a couple of years ago," said a spokesman

Other animals unnaturally out and about include bats - pipistrelles and noctules are making far more forays than they normally would at the time of year - hedgehogs, and moles, which are being driven close to the ground surface because of the high water table, after all the rain.

Neither the autumn's record wet, nor the recent remarkable warmth, can be directly attributed to global warming. But both of this year's phenomena are undoubtedly consistent with predictions of what climate change is expected to bring.

The sodden autumn, whose average 19.02 inches of rainfall over England and Wales smashed the previous, 1852 record by more than an inch, certainly qualifies as an "extreme event" in weather terms.

One of the most regular predictions by supercomputer models of the global climate is that a warming world will produce more extreme events in general, and more rain in particular, especially over the northern hemisphere in winter.

December's warmth is also consistent with recent observations.

Summers may not be much hotter, but winters are certainly less cold.