Mosquito-Borne Virus Spreads Across Southern England, Posing New Threat to Blackbirds

A mosquito-borne virus newly arrived in the UK has rapidly spread across large parts of southern England, sparking concern among scientists and conservationists about its potential impact on blackbird populations.

The Usutu virus, first identified over 50 years ago near the Usutu River in southern Africa, was detected in the UK for the first time in 2020. Since then, it has been found in blackbirds from Greater London to as far west as Dorset and as far north as Cambridgeshire, according to new data.

“Blackbirds specifically are quite susceptible to the virus and since 2020 we’ve found a decline in blackbirds of approximately 40% in Greater London,” Dr Arran Folly of the Animal and Plant Health Agency (APHA) said.

“It gives an indication that in the future we might get other viruses that are transmitted by mosquitoes emerging in the UK.”

Scientists from the Animal and Plant Health Agency (APHA) in Weybridge, Surrey, have been monitoring mosquito-borne diseases in wild birds for decades.

“We’ve seen that the virus has spread further than we thought it might do, and it’s persisted,” said Dr Folly.

There have been warnings that changing climate conditions—such as longer, warmer summers and increased rainfall—are creating a more favourable environment for mosquitoes, allowing them to thrive in areas where they were previously rare.

Usutu is known to cause illness and death in birds, particularly blackbirds, and has been linked to significant population declines in parts of mainland Europe. Though mass die-offs have not yet been observed in Britain, the virus’s spread has raised alarms, particularly given the additional pressures blackbirds face from habitat loss, pesticide use, and climate change.

While the virus poses a low risk to humans and has not caused any known human cases in the UK, it can also infect horses and, occasionally, people in other countries.

To better understand the virus’s impact and track blackbird populations, the APHA has partnered with the British Trust for Ornithology (BTO). Together, they are calling on the public to take part in a summer bird count by recording blackbird sightings in their gardens.

“Monitoring blackbird numbers is crucial,” said Lucy Love, a garden birdwatch ambassador for the BTO. “Around this time of year, they’re actively breeding and feeding their young, and we can learn a lot just by watching their behaviour in our gardens.”

Blackbirds, famous for their rich evening songs and familiar garden presence, remain one of the most common garden birds in Britain. Populations are generally stable in rural areas and the north of the country, but some declines have been noted in the virus-affected regions of the south.

Scientists hope that by gathering more data on blackbird numbers and the virus’s spread, they can better assess the risks and guide future conservation efforts.

Lucy Love, a garden birdwatch ambassador for the BTO, knows the blackbirds in her gardens by sight and has grown fond of them.

“They’re beautiful birds – intelligent, friendly and they have the most beautiful song with a lovely melodic tone to it,” she explained.

“And we cannot lose them – they’re a vital part of our ecosystem.”

 

 

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