Number of blackbirds in British gardens is plummeting because of mosquito-borne virus, charity warns

The number of blackbirds in our gardens is plummeting because of a mosquito-borne virus, a charity warns.

Populations are dropping, especially in London where the total fell 50 per cent in 2020, said the British Trust for Ornithology (BTO).

Numbers recovered,  but are still around 32 per cent lower now than in 2019.

The spread of the Usutu virus has been linked to climate change. It was first identified in South Africa before being detected in mainland Europe three decades ago and then in the UK in the summer of 2020.

Native UK mosquitoes can transmit the virus in warmer spells and humans can also catch it, although there have been no cases identified in the UK.

The Government said the Usutu virus led to the death of two people with weakened immune systems in Croatia and Italy.

The BTO added that although the risk was low, 'this is the first time in modern history that a mosquito-borne viral zoonosis (a disease which can be transmitted from animals to humans) has emerged in the UK.' 

Now scientists are trying to better understand the extent and spread of Usutu virus and what the potential impacts might be for the UK's Blackbirds.

Researchers are keen to see if anything similar is happening in other large cities across the UK, and how this compares to smaller urban and rural areas.

The BTO is appealing for people to take part in the Blackbirds in Gardens Survey to help their scientists better understand how Blackbirds use different types of garden, and what factors might influence the risk of disease transmission.

Importantly, the survey also seeks to determine how successful the birds are in rearing young, especially at different levels of urbanisation, from rural to urban gardens.

Dr Hugh Hanmer, senior research ecologist with BTO said: 'Blackbird numbers have been decreasing in Greater London for some time.

'However, from 2020 they started declining more strongly, which coincided with the detection of Usutu virus.

'There is now evidence of a wider decline in southern England, not seen in other UK regions. 

'The BTO survey seeks to understand why this change is happening and to identify any link to the emergence of Usutu virus. 

'By better understanding how Blackbirds use our gardens, we hope to halt the declines.'

Blackbird numbers in London fell by 50 per cent in July 2020. They recovered slightly but are still around 32 per cent lower now than in 2019.

Dr Arran Folly, senior scientist with APHA and Vector-Borne RADAR project lead said, 'Outbreaks of mosquito-transmitted diseases like Usutu virus, which is now endemic in south-east England, are likely to increase in the UK especially as temperatures warm in the wake of climate change.'

He added: 'I would urge any garden owners to take part and help us keep track of this virus.'

BTO is asking for anyone with access to a garden to take part in the survey.

To sign-up visit www.bto.org/blackbirds-gardens