RSPB Big Garden Birdwatch results for 2023 suggest disease trichomonosis is decimating chaffinch and greenfinch numbers

A parasitic disease spread by contaminated food and drinking water is killing some of Britain's most popular garden birds, says the RSPB.

The results of the latest Big Garden Birdwatch confirm that greenfinches and chaffinches are being hit hard by the disease known as trichomonosis.

Caused by the parasite trichomonas gallinae – infection makes birds' throats swell and causes them to regurgitate or reject food until they starve to death.

As a result the UK chaffinch population has declined by 34 per cent over the last decade, says the charity, while greenfinches have declined by 65 per cent over the same time frame.

But gardeners can unknowingly contribute to the spread of trichomonosis because it is passed through contaminated food and drinking water.

This means that bird feeders, bird tables and bird baths must be moved around to stop food waste building up, be regularly cleaned with a very mild disinfectant and never be filled with more than a couple of days worth of food at a time.

Pigeons and doves can also be at risk of the disease as can some birds of prey.

The Big Garden Birdwatch, conducted over a weekend in January, is the world's largest garden wildlife survey and gives the RSPB valuable insight into how garden birds up and down the UK are faring.

Other findings from this year's recordings include confirmation that house sparrows are the number one bird most frequently spotted in our gardens.

Yet despite this an estimated 22 million sparrows have been lost from our skies since 1966 according to numbers collated by ornithologists.

This year more than half a million people across the UK took part in the RSPB’s annual Big Garden Birdwatch, counting more than nine million birds.

The RSPB’s chief executive Beccy Speight said: "With so many people sending in their sightings over the weekend from across the UK, Big Garden Birdwatch really helps paint a picture of how our garden birds are faring.

"While we celebrate the 20-year stint of the house sparrow at number one, the numbers speak for themselves when it comes to the startling declines of some of our once common birds. We are in a nature and climate emergency. We’ve lost 38 million birds from our skies in the last 50 years."

Garden birds can be vulnerable to everything from disease to sudden and unexpected changes in the weather.

And results from the UK Butterfly Monitoring Scheme released in March, show that it isn't just birds which are being affected by sudden and dramatic changes in our climate.

Last year's heatwave and subsequent drought has also had a 'major negative impact' on UK butterfly species, latest studies have found. Prompting fears that insect numbers will be dramatically reduced this year as subsequent generations suffer.