Listen to the chiffchaff - and prepare for a hot spring

Never mind the forecast - look at the chiffchaff indicator. The movements of one of Britain's smallest birds confirm this is the best spring for several years.

The tiny olive-green warbler migrates to Africa every winter and is usually the earliest migrant bird species to return in March. Its repeated two-note "chiff-chaff" song is regarded by many as the first sound of spring.

But for past two years chiffchaffs have been returning later, in smaller numbers, hit by unsettled spring weather on their journey across the Mediterranean and on their return to Britain.

This year, however, numbers are back up. The changing pattern of chiffchaff arrival is visible on BirdTrack, the migration-monitoring website run by the British Trust for Ornithology. It shows that the average date for chiffchaff arrival went from 8 March in 2004 to 11 March in 2005 and then 22 March in 2006, but is back down to 10 March this year.

The information comes from the daily observations of more than 10,000 birdwatchers.

But meteorological observations are also confirming the picture. "We are having a really warm spring," said a Met Office spokesman. For the past week, maximum daytime temperatures in much of Britain have been far above their seasonal average, with some areas seeing the thermometer creeping up to 20C when normally it would be hovering around 12C-13C.

This weekend will be even warmer, with temperatures in London likely to hit 24C - that's more than 75F - when normally they would be 13C. Even Aberdeen, on average about 9C-10C at this time of year, will probably reach 19C (66F). A high-pressure system over the British Isles is producing settled weather with clear skies and warm, sunny days, although the nights have been cooler and closer to the seasonal average.