The RSPB is encouraging Londoners to watch their garden birds this weekend, to help understand more about environmental change.

To get involved in the Big Garden Birdwatch, people need to take just one hour counting the birds in their garden or local park, and record the highest number of each bird species seen at any one time.

RSPB London representative Tim Webb said: “Annual results are interesting, but it’s the long-term trends that are important. Seeing how different species are faring over time gives us a snapshot of the state of London’s environment.

“Birds are among the first species to mirror environmental change.”

Last year, London recorded drops in numbers of house sparrows, starlings and blackbirds. Blue tits, goldfinches and greenfinches did well. Results from the 2012 survey will show whether these are continuing trends that set-off alarm bells or less alarming natural fluctuations.

For more information, visit rspb.org.uk/birdwatch.