How climate change has helped Little Bastard and his badger pals to prosper as never before

Britain's badger population has soared in the past 15 years, and the likeliest explanation is climate change, research is showing.

Milder and wetter autumns have increased the availability of earthworms, the British badger's principal food, prompting an astonishing rise in numbers.

In one big wood near Oxford, where the animals have been studied more intensely than anywhere else, their numbers trebled from 100 to 300 just in the decade from 1987 to 1997 (although they have now fallen back to 250). Nationally, badgers are thought to have increased from about 270,000 to between 320,000 and 350,000 over the same period, although this may well be an under-estimate.

The huge rise in numbers of one of Britain's favourite wild mammals is one of the most remarkable effects yet seen of Britain's steadily warming climate, which has already produced well-documented cases of earlier egg-laying in birds, earlier leaf emergence in trees and a longer growing season.

It fits in with the fact that most of the warming observed so far is resulting in wetter, less cold winters rather than hotter summers (although record-breaking 2003 has shown that the summers are now getting hotter too).

The new weather regime means that earthworms are much more likely to come to the surface of the soil in the autumn and winter months, which cannot happen when the ground is dry or frozen. Badgers can go on feeding for longer late in the year and are in much better condition to produce their young in spring.

The phenomenon has been clearly observed in Wytham Woods near Oxford, where the animals have been studied intensely since 1987 by the Wildlife Conservation Research Unit (WildCRU) of Oxford University, helped by hundreds of volunteers from the environmental charity Earthwatch Europe.

The broadleaved woodlands, 1,000 acres in extent, have always held a substantial population of badgers and when the study began they numbered about 100. But over the next 10 years the population tripled.

Although other reasons could be adduced to account for the rise, such as agricultural change or new legal safeguards for badgers - the Protection of Badgers Act, 1992, made it an offence to disturb a badger's sett - climate change is by far the likeliest explanation, says WildCRU's Chris Newman, who runs the badger project with Professor David Macdonald.

"Some people might say that badger numbers have exploded since they were given added legal protection, and people were no longer shooting them or digging up their setts," Dr Newman said. "But it doesn't apply to Wytham, because this has been a nature reserve where badgers have been undisturbed since 1943. We can rule out the effects of national protection here - nothing has changed for 60 years.

"Similarly, although there were changes in agricultural land use earlier, in the period 1987 to 1997 there were no significant changes at all, so that can be ruled out.

"But what we can say is over that period, every year was milder than the previous one, and the autumns were wet. The availability of earthworms increased enormously as a consequence, and we think this is what has led to the population expansion."

However, Dr Newman said, numbers had now reached a peak and had fallen back - and another effect of climate change was responsible for this too: a succession of drier springs.

"Dry springs mean badgers cannot get their earthworms, and other food sources, such as crops or beetles, are not yet available, so there is higher mortality, especially among the cubs," he said.

The whole process means that badger numbers in Britain are not increasing endlessly but have now reached a new equilibrium - but one that was much higher than before. "We can say that the carrying capacity of the countryside for badgers has increased substantially," Dr Newman said.

The 33-year-old research biologist lives in the heart of Wytham Woods with his partner Dr Christina Buesching, another badger researcher, and has got to know many of the animals as individuals. Badgers from a nearby sett frequently come to The Chalet, the old hunting lodge where the researchers live, seeking food, and sometimes they attempt to break in.

One animal, badger No 32 or "No Ears", announced himself on Dr Newman's first night in the woods by noisily eating potato peelings at three in the morning. On another occasion he was caught in the kitchen with his paws around a bag of dog biscuits, trying to drag it back to his sett. "When he saw me he sort of shrugged his shoulders, and left it," Dr Newman said. A current visitor is badger No 478, familiarly known as - ahem - "Little Bastard". He has a pink nose and takes food from Dr Newman's hand, but his speciality is breaking into the researchers' lavatory and drinking the water - also in the small hours of the morning.

Dr Newman, who takes a droll view of the badger world, describes Little Bastard's characteristics as follows: "He was born in 1995 at an adjacent sett (in front of the Chalet) and has only recently moved to Chalet sett ... he weighed 9.2kg in July, had a low flea score, modest toothwear ... and he would like to work for world peace."

* People wanting to join the badger and other mammal monitoring projects at Wytham Woods as Earthwatch volunteers can find details by calling 01865 3188831, or by accessing www.earthwatch.org/europe