Woodland Trust

Nature's CalendarNature Detectives

Bluebells are just starting to flower

Spring trends
Nightingale. Dietrich

Over the past 40 years phenology has provided biologists with clear evidence that spring is arriving earlier.

Trees have been coming into leaf sooner. Migrant birds are arriving earlier with swallows now a week ahead of their dates in 1970. Frogspawn is being spotted before Christmas in the south-west, while comma and holly blue butterflies have been sighted as early as March.

The variation of timing between species remains disturbingly evident, with all taxa changing at very different rates relative to 2001; plants about 10 days earlier, insects 2 weeks earlier and bird activity (migration and breeding) about a week earlier.

Butterflies like it hot

The Butterfly Monitoring Scheme has shown that the emergence of butterflies in early summer varies with temperature. The ringlet is an excellent example. Its appearance has become progressively earlier in recent years, for every 1°C rise it can be seen a week earlier.

Bursting into bud

Records from Jean Combes in Surrey are positive proof that the leafing of trees has advanced since the 1980s. Horse chestnut shows the greatest advance of 12 days, oak 10 days and ash six.

Early birds

Migratory birds are also responding to climate change. Records from coastal bird observatories from 1960-96 show that two woodland species - chiffchaff and blackcap - appear to be arriving in Britain earlier. Their response to temperature rise is about two to three days per 1°C. If you are interested in birds, take a look at the British Trust for Ornithology’s Birdtrack website to view the pattern of arrival of migrants in spring.