Move over cuckoos. In this era of global warming the chiffchaff has become the harbinger of spring.

The first sightings of chiffchaffs in Britain this year were reported yesterday prompting bird watchers to proclaim that spring has started.

It joined a wealth of indicators that spring has well and truly arrived, including frogspawn in northern Scotland, butterflies by the score and flowers everywhere.

This time last year the country was still in the grip of snow and Arctic winds.

Yesterday Gravesend in Kent recorded 18C (64F), the highest temperature of the year so far — whereas in 2006 it was late April before similar warmth was felt.

So warm has this March been that deckchairs have appeared on Bournemouth’s beaches and people have been eating in the garden.

Swallows have not waited for summer proper: they have been here for more than a fortnight, the first seen on February 23 in Glamorgan.

But the cuckoo has failed to keep up with the times, while other migrant birds arrive earlier than they did in decades gone by.

Spring watchers at the British Trust for Ornithology now regard the chiffchaff as a far better indicator of when spring has started.

Paul Stancliffe, of the organisation, said that the chiffchaff was chosen because, like the cuckoo, it is easily identified by its onomatopoeic call but — unlike the cuckoo _— it arrives as spring starts in the 21st century.

“It’s easy to identify from its call and consequently when people submit reports about having heard it there can be no mistaking them for anything else,” he said.

“With the cuckoo we have the problem that it’s sometimes confused with collared doves and, more importantly, it’s in steep decline so fewer of them are arriving.”

In 2002 the chiffchaff was first reported on March 8 but in the last couple of years the date has been pushed back by cold snaps. Last year it arrived on March 22, ten days later than this year.

Tim Sparks, of the Centre for Ecology and Hydrology, which records seasonal data to monitor changing times of spring and autumn, said that by most measures spring can be said to have started. “We’ve seen 5,764 reports of frogspawn — they started very early this winter,” he said. “There have been several migratory birds arriving, there have been plenty of butterflies and, on Sunday, there was a hummingbird hawkmoth.”

Among the butterflies that have been reported are the brimstone, and yesterday alone there were sightings of peacocks, small tortoiseshells, red admirals and commas.

Dr Sparks added: “People have lots of different ideas of when spring has come. I tend to think of hawthorn being in leaf as a sign of spring and once I’ve seen a holly blue butterfly I know it’s really here. It feels like holly blue weather now but I’m still waiting to see my first.”

The Met Office is less lyrical. For ease of statistical analysis it regards March 1 as the first day of spring, whatever the weather.

Signs of the time

Cuckoo
Cuculus canorus

Sound: “Coo-cooo”

Arrives: April

Leaves: August

Eggs: Up to 25 — in other birds’ nests

Weight: 106-133g

UK breeding: 13,000-26,000 pairs

Numbers: down 44 per cent from 1970-2004

Description: Adult birds usually have blue-grey head, breast and upper parts; horizontal barring on underparts and white spots and tips on the tail. In flight, can be easily mistaken for a Sparrowhawk or Kestrel

Chiffchaff
Phylloscopus collybita

Sound: “chiff chaff”

Arrives March

Leaves September

Eggs: 4-7

Weight: 53-64g

UK breeding: 690,000 pairs

Numbers: 40 per cent rise in numbers from 1997 to 2004

Description: In spring and summer they have brownish-green upper parts and buff underparts. There is a dark eye stripe through the eye, a pale eyebrow (supercilium) and thin pale eye ring. The Chiffchaff is practically indistinguishable from the Willow Warbler, though it is less yellow and often has darker legs