A deadly disease is having a devastating impact on bird populations, an ornithological enthusiast was warned.

Greenfinch populations in Sussex are thought to have dropped by up to a third and chaffinch populations by a fifth, according to a study by the Garden Bird Health Initiative.

The garden birds are suffering from trichomonosis, a parasite which infects the digestive system of mostly finches, doves and pigeons.

It causes lesions in the throat which makes it hard for the bird to swallow food leading it to die of starvation.

Affected birds appear “puffed-up” with fluffed-up plumage and are generally lethargic.

Peter Calladine, member of the Royal Society for the Protection of Birds (RSPB) and Royal Ornithological Society, said: “It’s very bad news. It is very widespread and causing huge losses to the bird population in Sussex. The numbers have fallen terribly. We are talking thousands.

“Greenfinches seem to be the most affected. The disease is very distinctive. They get all puffed up and it’s quite obvious they’re dying.”

The Argus:

The bird-watcher notified the society after finding two dead greenfinches on his Lewes balcony in a week.

Mr Calladine added: “We had thought several of them had looked rather odd. They were all puffed up as if against the cold, yet it was summer. We thought they must be due to moulting, but no.

“The parasite lives in the bird’s digestive tract. It progressively blocks the bird’s throat, making it unable to swallow food. The bird dies from starvation.

The RSPB is advising birdlovers to remove and clean bird feeders from their gardens if they see infected birds.

Sam Stokes, of the RSPB, said: “If you think you have affected birds in the garden you should remove your feeder for up to a month and thoroughly clean it before you put it back.

“It stops birds congregating together which is how the disease spreads.”

Sussex Ornithological Society secretary Val Bentley, of Henfield, said: “It’s very sad but there’s not much you can do other then make sure your feeding station is kept clean.”

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