The blackbird is one of the UK's most common birds. But in recent years the mellifluous songbird has experienced a change in fortunes, with a drop in numbers reported by garden birdwatchers, particularly in Greater London.
British Trust for Ornithology (BTO) scientists think a new virus, first detected in London in 2020, may be accelerating the decline of blackbirds in the UK.
The Usutu virus (USUV), originally discovered in the 1950s in Africa and present in Europe for the past three decades, is carried and transmitted by mosquitoes. Culex pipiens, or the common house mosquito, is one of the main culprits – the species is native to the UK and is ornithophagic, meaning bird-biting.
It’s thought the virus is spread by migrating birds.
Although USUV has been found in a number of wild birds, and some captive great grey owls, large-scale mortality seems to have been limited to blackbirds in Europe.
“The overall fatality rate is unknown but the Usutu virus causes systemic infection in blackbirds, affecting multiple organs including the brain,” Hugh Hanmer, senior research ecologist at the BTO and one of the survey’s leads, told BBC Wildlife.
“Affected blackbirds are most often found dead without prior evidence of ill-health.”
This is the first time that a viral mosquito-borne zoonosis (infections that can pass between animals and humans) has emerged in wild animal hosts in the UK. However, the risk to humans is considered low, with no cases of the virus found in humans in the UK. Most USUV infections in humans are asymptomatic and do not cause disease.
How to help blackbirds
The BTO is calling on the public to take part in their new citizen science project called the Blackbirds in Gardens survey, which will form part of their research into the impact of the virus on blackbirds. The survey, which involves reporting blackbird numbers and behaviours in your garden, will provide insights into how blackbirds use gardens and raise their young.
If you find a sick or dead blackbird, or other dead garden wildlife, you are advised to report it to the Garden Wildlife Health website.
In addition to the Blackbirds in Gardens survey, scientists from the Vector-Borne RADAR project will be sampling mosquitoes and other wild birds to detect the spread of the virus across the country.
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