Blackbirds are in rapid decline in England. Now scientists are worried that a new virus, first recorded in London in 2020, may be contributing to the songbird's ill fortunes.
When infected with the Usutu virus (USUV), blackbirds can become lethargic and weak, but are often found dead without previous signs of illness.
USUV was originally discovered in South Africa in the 1950s and has since spread elsewhere due to bird migration. Present in Europe for the past three decades, where it has been linked to avian mass mortality events, it was first detected in London during the summer of 2020.
And it may be on the move once more, says experts from the British Trust for Ornithology (BTO), who are concerned that the virus appears to have started to infect blackbirds across south-east England.
“There is now evidence of a wider decline in southern England, not seen in other UK regions,” said Hugh Hanmer, one of the survey’s leads and a senior research ecologist at the BTO.
How you can help blackbirds
In a bid to redirect the fate of the blackbird, a new citizen science survey is being launched to study the impact of a virus on the UK’s beloved songbird – and members of the public can contribute their garden sightings to help scientists.
The survey hopes to compare the numbers and behaviours of blackbirds in different levels of urbanisation. “By better understanding how blackbirds use our gardens, we hope to halt the declines,” said Hanmer.
You can take part in the Blackbirds in Gardens survey by signing up on the BTO website and submitting your sightings. You will need to watch your garden for a minimum of 15 minutes each week until October, during which you will record the peak number of male, female and juvenile blackbirds, and their behaviours. 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.
How does the Usutu virus spread and can humans catch it?
In Europe, one of the main vectors for the virus is the Culex pipiens mosquito, an ornithophagic (bird-biting) species that's also native to the UK.
The mosquito species does occasionally bite humans, but the virus’ risk to humans is considered low. No cases of the disease caused by USUV have been detected in humans in the UK, and only a small number of cases in Europe have been reported. The infection is usually asymptomatic (does not cause disease) in humans.
This is the first time that a mosquito-borne viral zoonosis – a disease that can be transmitted between animals and humans – has emerged in wild animal hosts in the UK.
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