The weather has forced their diet of worms too far underground for the birds to feed.
As a result, gardeners have witnessed blackbirds resorting to desperate measures to avoid going hungry.
They have been waiting on freshly-watered lawns ready to pick up worms that rise to the surface.
Blackbirds have also been eating tadpoles and young slow worms, and snatching baby mice from their nests.
The mistle thrush and song thrush have also been affected by the unseasonably warm weather.
Paul Stancliffe, from the British Trust for Ornithology, said an annual survey of 250 birds has shown the average weight of a blackbird has plummeted from 130g to 90g this year.
He told the Daily Telegraph: 'The birds have got once chance left for another brood this year and if the weather doesn’t change, things look pretty bleak.
'Taking tadpoles, slow worms and mice is not normal behaviour.' Read More