Thousands of migrating birds have been dying before reaching England this week because of an appalling combination of fog and winds around the coast, according to the Royal Society for the Protection of Birds (RSPB).
Some fishermen have told the charity of the deaths of many exhausted and disorientated "garden" birds plunging into the sea around their vessels, a spokesman said.
England's east coast, from Northumberland to Kent, has seen the arrival of many birds, including redwings, fieldfares, bramblings and blackbirds, perhaps numbering in their millions.
The charity said these were the lucky survivors which had managed to cross the North Sea, but many others might have perished before making landfall.
Ian Kendall, reserves manager at the RSPB's Bempton Cliffs reserve in North Yorkshire, said: "There are birds in their thousands, on the cliffs, in the surrounding fields, hedgerows and along the length of the Yorkshire Coast.
"The birds left Scandinavia in glorious sunshine but as they crossed the North Sea, they flew into fog and rain, so they stopped off at the first bit of land they have come across."
Along the south coast, the RSPB has received several reports of thousands of disorientated and exhausted birds drowning in the sea.
The skipper of a boat said: "While fishing about 10 miles south of Portsmouth, we witnessed thousands of garden birds disorientated, land on the sea and most drowning. Species included goldcrests, robins, thrushes and blackbirds. The sky was thick with garden birds. I estimate I saw 500 birds die and that was just in our 300-yard sphere."
Martin Harper, the RSPB's conservation director, said: "The scale of these reports is truly shocking, and it has the potential to adversely affect the status of species which may be declining for other reasons."
Exhausted birds which have made it to the UK will be looking for food and may be visiting gardens, especially as the weather is expected to turn colder.
Ian Hayward, an adviser with the charity's wildlife inquiries team, said: "The first cold snap will encourage many birds to visit gardens increasingly, in a quest for food. Now is the time to start topping up bird tables and feeders.
"These birds need all the help they can get, so gardeners and farmers can also help birds by not cutting hedgerows laden with much-needed berries."