Early springtime is causing food shortages for bird populations that are now out of sync with their breeding calendar due to global warming, the Woodland Trust is warning.

Signs of early spring such as first sightings of brimstone butterflies (pictured) have been made two weeks earlier than usual, as well as the first leafing of trees, observations have revealed.

It may be causing devastation to blue tits unable to catch up to the earlier spring calendar when insect food source is at its height — too early for their chicks that are not ready to hatch.

“Change has happened very quickly,” Woodland Trust’s Dr Judith Garforth warns. “The best option to help wildlife would be to slow down the spring by reducing CO2 emissions.

“We need to plant more trees and to keep tracking nature’s response. The trend of earlier springtime is becoming the new ‘norm’.”

Blue tits have reacted slowly to the change which could soon be permanent.

Leafing of trees like the elder, larch, rowan and oak have been about two weeks before the annual average.

“An elder in leaf was much earlier than I would expect,” Dr Garforth adds. “Our data provides the clearest evidence of a changing climate affecting wildlife.”

Met Office data showed temperatures in February at 2.2C above average, making it the warmest on record, while the Spring Index comparing modern and historic data is running almost nine days earlier.

The ecological food chain has become ‘mismatched’ or out of sync, the trust has found. Oak trees leafing earlier means an earlier peak in the number of moth caterpillars, which blue tits are not matching with their breeding timing when their chicks were traditionally at their hungriest when caterpillar numbers were at their highest.

It also affects some insect populations, adding more shortage to the food chain.  

“We see insects emerging early before there are many flowers in bloom to provide a food source,” Dr Garforth adds.

More volunteers are needed as ‘citizen scientists’ for the trust to keep Britain’s 300-year-old tradition of observing nature active, to be able to compare today’s global warming temperatures with historic records of the past.