A mosquito-borne illness, the Usutu virus, has spread in the UK with alarming speed, threatening our native blackbirds and prompting urgent scientific research. This disease, spread by infected mosquitoes, correlates alarmingly with a decline in some blackbird populations. Since its emergence, the disease has accelerated across southern England within five years, with experts concerned about the impacts of climate change on disease vectors. To assess the damage to blackbird populations, scientists are rallying garden owners to engage in critical counts.
The British Trust for Ornithology has launched ‘The Blackbirds in Gardens’ initiative, stating: “The Blackbirds in Gardens project will help us understand how Blackbirds use gardens, and the potential effects of the Usutu virus on their population in the UK.” Bird enthusiasts can contribute observations through the counting system, and the BTO encourages participation: “If you have access to a garden, have an interest in garden birds, and can recognise a Blackbird by sight, then this survey could be for you!”
This crucial data-gathering exercise is now open for registration and continues until September. The project is part of the Vector-Borne RADAR initiative, a collaboration with the Animal and Plant Health Agency, the UK Health Security Agency, and the Zoological Society of London.
“We’ve seen that the virus has spread further than we thought it might do, and it’s persisted,” Dr Arran Folly from the Animal and Plant Health Agency (APHA) told the BBC. The APHA experts, based in Weybridge, Surrey, have been monitoring mosquito-borne diseases in wild birds for years, amid rising fears that climate change is transforming Europe into a potential breeding ground for these pests.
Extended summers, increasing temperatures and heavy rainfall are creating conditions favourable for these pesky insects to infiltrate areas previously unsuitable for them. Until 2020, all test results were negative.
However, following the heatwave in the summer of that year, Usutu was detected in several blackbirds in Greater London. “Blackbirds specifically are quite susceptible to the virus, and since 2020, we’ve found a decline in blackbirds of approximately 40% in Greater London,” disclosed Dr Folly.
“It gives an indication that in the future we might get other viruses that are transmitted by mosquitoes emerging in the UK.”
Diseases like Usutu pose a growing threat to wild birds, alongside a variety of other challenges, including habitat loss, climate change and pesticide use.
What is Usutu?
The Usutu virus, first identified over half a century ago near the Usutu River in southern Africa, has now been detected in wild birds across a large part of southern England. This virus, which has spread globally and reached Europe three decades ago, was found for the first time in the UK in 2020.
Blackbirds are particularly vulnerable to this virus, which can also affect horses and occasionally humans. However, it is generally considered low risk to humans, with no reported cases in the UK so far.
The virus has now been found in wild birds across a broad area of southern England, stretching as far west as Dorset and as far north as Cambridgeshire. The exact threat that Usutu poses to wild birds remains unclear.
While the virus has been associated with mass blackbird deaths in other parts of Europe, this doesn’t appear to be the case in the UK. Despite the presence of the virus, the blackbird remains one of the most common garden birds, with stable populations in many regions, particularly in rural areas and the north.
To solve this mystery and gather more data on blackbird numbers, scientists have joined forces with the British Trust for Ornithology (BTO). They’re appealing for volunteers to count blackbirds in their gardens during the summer months to gain further understanding.
During this season, blackbirds are actively breeding and raising their young, often seen hopping along the ground or singing from tree branches on warm summer evenings.