Wildlife: Do they know it's Christmas?

After the warmest summer on record, birds that should be in the tropics are still here, leaves are still on trees and insects that should be dead are feeding well. Is this proof of global warming?

It may be just over a week to go until Christmas but parts of the natural world are behaving as if it were still late summer. Many trees are hanging on stubbornly to their leaves, wild plants are in flower and dragonflies, bumblebees and even butterflies can still be seen in the garden. Swallows and house martins, which normally would be south of the Sahara by now, have been sighted all over Britain, from North-umberland to Norfolk.

Experts say the delayed winter of 2006, in what will be Britain's hottest recorded year, could be one of the starkest signals yet that global warming has potentially far-reaching impacts for the UK's wildlife.

This year, swaths of southern and central England have been virtually untroubled by frost even though winter is nearly a third of the way through and the solstice only days away.

The months of September, October and November were the warmest in central England since 1659. The provisional UK-wide mean temperature in autumn was 11.3C, beating the previous record set in 2001 of 10.5C, in a temperature series that began in 1914. The UK Met Office predicts a 40 per cent chance that winter temperatures will be above average with only a one in four possibility they will be colder than normal. This unprecedented warmth has altered the behaviour of many plants and creatures.

Scientists are concerned that with spring arriving earlier and autumn lengthening, chaos and confusion could become the norm in nature. The changing seasons could upset the delicate interdependence between nature, plants and animals and increase competition for food.

The Woodland Trust is asking members to report trees, such as oak, which are still in leaf, preparing for a rerun of last year's "green Christmas", the first time many parts of the country experienced such a phenomenon.

Elsewhere, wild plants suggestive of summer, from oxeye daisies and field scabious to ragwort, are still in bloom, and late-flowering ivy is providing a good source of nectar for butterflies and other invertebrates.

Buff-tailed bumblebees, which are normally killed off by the first frosts (leaving only the queen to over-winter in hibernation) are still out foraging in gardens across Britain, says Professor Dave Goulson of the Bumblebee Conservation Trust, based at University of Stirling.

"The bees seem to have gone a bit haywire and it appears to be spreading," Professor Goulson said. "They normally have a rigid cycle and this time of year they should all be hibernating but something has gone wrong."

This winter, the BCT has been compiling reports of winter bumblebees as far north as Nottingham and York. Traditionally, the queens who have been underground since September, do not start emerging until March and April to look for a new nest-site and begin rearing their young. The nest grows through the season and reproduces around July or August, then the mated queens start their long winter hibernation again.

"This one species has started recently appearing in the middle of winter when by rights there shouldn't be any bumblebees left," the professor says. "It's not just queens but worker bees, which means there are nests alive and thriving through the winter."

And red admiral butterflies, which should also be hibernating, have been seen on the wing in several places, says the UK Phenology Network which monitors the timing of natural events. Its supporters provide the backbone for the spectacular success of the BBC's Spring and Autumnwatch programmes.

"We're also getting sightings of dragonflies," says Dr Tim Sparks, of the Centre for Ecology and Hydrology at Monk's Wood, Cambridgeshire, who is the network co-ordinator. "This is unusual for December. Normally, they would pack up shop in September or October, and killed off by the first frosts. But there have hardly been any frosts."

The number of migrant birds which have chosen not to migrate is a talking point with birdwatchers. They traditionally move south to warmer winter climates because they need a regular supply of aerial insect food not normally available in Britain during the November to March period. But many are still here, meaning the food must be available. Insect-eaters which have stayed include a whinchat at the Newport Wetlands, Gwent, garden and willow warblers at Prawle Point, Devon, and a common whitethroat at Putnoe, north of Bedford.

Ospreys, the spectacular fish-eating hawks, migrate to West Africa because catching fish is easier in hot tropical lagoons. Unusually, two are still in southern England, one at Nayland, Suffolk, another at Exeter, Devon.

Some seabirds that also should be in West Africa by now have still to depart: sandwich terns have been reported at Emsworth Harbour, Hampshire, and Studland, Dorset, and a roseate tern is reluctant to leave Dun Laoghaire, Dublin.

And many typical winter visitors to Britain have yet to arrive owing to mild weather across the North Sea. A woodcock, a long-billed gamebird that flew on to the pitch at St James's Park in Newcastle during the Newcastle-Reading match on 8 December, causing the game to be halted, was a newly arrived bird that should have flown in during October. Comparatively few smew, a type of diving duck, have arrived because the Baltic region freeze-up that pushes them westward has not happened yet. For similar reasons, there had until this week been only a small number of reports of berry-eating waxwings which normally come in from northern Russia and Scandinavia.

It is possible that the record for the warmest winter, set in 1988-89, will be broken. But the Met Office long-range forecast says the El Niño conditions which cause rising sea temperatures in the Pacific could lead to colder than normal spells in Northern Europe in 2007.

Swallows (Hirundinidae)

Small, fast-flying insect feeder, with long distinctive tail streamers. Once bred commonly in Britain, but numbers have declined due to habitat loss. Overwinters in southern Africa where habitat is also threatened. Have been spotted across England this December.

Oxeye daisies (Leucanthemum vulgare)

Native grassland wildflower found in meadows and open woodland, normally flowers between May and October. In superstition are said to represent the souls of dead children. Despite flourishing this year the daisy requires cold winters to initiate blooming.

Buff-tailed bumblebee (Bombus terrestris)

One of the most widespread UK bumblebees is normally the first to be spotted in spring. Fertilised queens survive winter underground between September and March while workers are killed off. This year have been spotted foraging in gardens as far north as York in December.

Oak (Quercus rober)

The classic English or common oak is found in mixed woodlands or growing as huge isolated specimens in open countryside. Its flowers appear in April-May, while its fruit ripens from September to October. Leaves usually drop in November, although last year many were still in leaf on Christmas Day.

Smew (Mergellus albellus)

The small, compact diving duck is normally spotted in small numbers on estuaries, lakes and reservoirs between the Wash and the Severn. It usually arrives in Britain from Russia and Scandinavia during December. Few sightings have been recorded this year.

Ivy (Hedera helix)

Common evergreen climber that sprawls along open ground and easily identifiable by its glossy three- to five-lobed leaves. Yellowish green flowers provide a valuable source of nectar to late flying insects. Still blooming in some areas.

Osprey (Pandion haliaetus)

Core UK population of this spectacular fish- eating raptor reside in Highland forests, lochs and rivers. Numbers have dwindled due to persecution. Spends each winter in West Africa, migrating via lakes and reservoirs. Seen in Suffolk and Devon.

Common darter dragonfly (Sympetrum striolatum)

One of the shorter species found in the British Isles, it is distinguishable by its dart-shaped abdomen. This dragonfly is usually seen between mid-June and October, when it basks on warm surfaces. Earlier this month it was spotted as far north as the Delamere Forest in Cheshire, and it has also been seen in Norfolk and Hampshire.

Red Admiral butterfly (Vanessa atalanta)

Dark chocolate brown/black body with red, orange and white wings is one of the most readily identifiable garden butterflies in the UK. Feeds on flowers and rotting fruit, killed by first frosts. Spotted in December in southern England.