The blackbird, the Netherlands’ most common breeding bird, could be in trouble, according to bird monitoring organisation Sovon.

At the last count the number of blackbirds in cities and villages had fallen by 15%, the highest percentage since counting began in 2007, the organisation said.

‘We have counted tens of thousands fewer blackbirds than last year. That means you will really hear fewer blackbirds in your neighbourhood,’ Sovon spokesperson Albert de Jong told broadcaster NOS.

A likely cause for the decline in blackbird numbers is the Usutu virus which originated in South Africa and was probably brought to Europe by migrating birds.

The virus, which is transferred by mosquitos, felled hundreds of thousands of blackbirds in Germany in 2012. The birds usually fall ill in summer because the mosquitos are at their most active at that time.

When the virus strikes the birds become listless, and in the final stages of the disease they develop bald spots on their heads and die.

Sovon asks anyone who spots a dead bird to report it so the cause can be established. Sovon is working with the virology department of the Erasmus hospital in Rotterdam to this end.

Despite the declining numbers the blackbird is still the most common bird in the Netherlands. ‘You know him by his dreamy, melodious song. Every garden has at least one blackbird.’ De Jong told the broadcaster.