"Our notion of what spring means and what happens in spring is changing. Nature is beginning to respond to a warmer climate," said Dr Kate Lewthwaite, the Trust's Nature Calendar Manager.

"There are a lot of early sightings such as active ladybirds and butterflies out and about. We have had confirmation of frogspawn seen as early as December and even tadpoles hatched already," she told Reuters.

Despite wintry blizzards across northern England and the Midlands, January was much warmer than normal.

The Met Office said this January's UK average temperature was 5.3 degrees Celsius (41.54 Fahrenheit) -- almost 2 degrees warmer than the 30-year January average of 3.4 Celsius (38.12F).

January 2007 was the second-warmest on record, clocking in at 6 Celsius (42.80F).

Other key sightings by the Woodland Trust's volunteers include snowdrops as far north as the tip of Scotland and nest-building rooks hard at work in the southwest, Oxfordshire and Surrey just before Christmas.

The Trust says it would not normally expect to see nature so active until between mid-February and May.

Frogspawn was spotted on Christmas Eve in Penzance, Cornwall and tadpoles a month later in neighbouring Devon.

"It's tempting to say 'wow' but from a frog's perspective it's a calamity," said Lewthwaite.

"The frog is vulnerable, easily fooled into breeding too soon and the spawn can then be vulnerable to freezing," she added.

The Trust says that nature coming to life too early can also cause problems in the food chain, with insects responding faster to the warmer temperatures than some species of birds. Experts fear birds may be missing out on prime feeding.