People are being urged to spend an hour this weekend counting the birds in their garden, park or local green space for the world’s largest survey of garden wildlife.

More than 9m birds were counted last year by 600,000 participants in the RSPB’s Big Garden Birdwatch, providing a vital snapshot of how wild birds are faring.

This year’s survey will reveal whether the recent cold spell across Britain has adversely affected numbers, particularly of smaller birds such as long-tailed tits and wrens, which struggle in prolonged cold.