A warm spring has brought about the early arrival of some UK wildlife, the first results of the Springwatch 2007 survey suggest.
Over the past few months, amateur naturalists have logged more than 24,000 first sightings of six key species of plants and animals.
Some, such as the peacock butterfly and frogspawn, have been spotted earlier than expected.
The Woodland Trust said it was worried "because the changes are so rapid".
Springwatch, now in its third year, is run by the Woodland Trust and the BBC.
The survey data is being compiled to build up a picture of the season as it unfolds across the UK so that it can be compared to previous years.
As the survey has been running for a limited time, the results cannot be interpreted as definitive guide to how a changing climate is affecting wildlife, but researchers are already examining the data for trends.
Recent weather in the UK has been extremely mild, and records show it has been the warmest spring since the Springwatch survey began in 2005.
Nick Collinson, head of conservation policy at the Woodland Trust, believes the warm conditions may be responsible for some earlier-than-expected sightings.
He said: "This has been our earliest Springwatch year, well ahead of the normal time we would have expected to see these events 30 years ago."
Members of the public were asked to record the dates they have first seen red-tailed bumblebees, frogspawn, flowering hawthorns, seven-spot ladybirds, peacock butterflies and swifts.
Some of the preliminary findings of this year's survey include:
Frogspawn spotted on average two weeks earlier than in 2006 and three weeks earlier than the "phenological norm" (an average first-sighting date based on data gathered over the last 30 years).
Peacock butterflies sighted on average one month earlier than 2006, two weeks earlier than 2005, and one month earlier than the norm.
For swifts, the data is still returning, but initial results suggest the date has stayed much the same as 2006, 2007 and the phenological norm.
Mr Collinson was worried about the possible impact of increasingly warm springs.
He said: "We are concerned because the change seems to be so rapid.
"And we know there is a mismatch of timing, so, for example, when insects would pollinate flowers, the flowers are coming out earlier than the insects are available, and we know this is happening.
"It is very difficult to tell what that means, but certainly we know that wildlife is under pressure."