A mosquito-borne virus newly detected in Britain is spreading swiftly across southern England, prompting growing concern among scientists for the nation’s iconic blackbirds.
The Usutu virus, first identified in the UK in 2020, has been found in wild birds as far west as Dorset and as far north as Cambridgeshire. Transmitted by infected mosquitoes, the virus poses a particular threat to blackbirds, a species already under pressure from habitat loss, pesticide use and climate change.
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Researchers from the Animal and Plant Health Agency (APHA) in Weybridge, Surrey, have been tracking mosquito-borne diseases in wild birds for decades. Speaking to the BBC, Dr Arran Folly of the APHA said: “We’ve seen that the virus has spread further than we thought it might do, and it’s persisted.”
The virus was first detected in blackbirds in Greater London following the intense summer heatwave of 2020. Since then, scientists have observed a striking 40% decline in the local blackbird population. “Blackbirds specifically are quite susceptible to the virus,” Dr Folly explained. “It gives an indication that in the future we might get other viruses that are transmitted by mosquitoes emerging in the UK.”
The spread of mosquito-borne diseases like Usutu is likely being accelerated by climate change. Warmer temperatures, longer summers and periods of heavy rainfall are creating favourable conditions for mosquito populations to thrive in areas that were previously inhospitable.
While the Usutu virus has caused mass blackbird die-offs in mainland Europe, the impact in Britain appears to be less severe so far. Blackbird numbers remain stable in many rural and northern parts of the country, and the species remains one of the UK’s most common garden birds.
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To better understand the virus’s impact, the APHA has partnered with the British Trust for Ornithology (BTO) to monitor blackbird populations more closely. They are now calling on members of the public to report sightings and monitor the presence of blackbirds in their gardens throughout the summer months.
Lucy Love, a garden birdwatch ambassador for the BTO, has formed a close connection with the blackbirds visiting her garden. “I recognise them by sight,” she said, highlighting the role that citizen science can play in tracking the health of local bird populations.
Blackbirds are currently breeding and raising their young, often seen foraging on lawns or singing from tree branches in the early evenings. Their future, however, may depend in part on how Britain confronts the growing ecological challenges posed by a warming climate.
