Many of the common species are in decline, the RSPB says
Hundreds of thousands of people are expected to have played a part in this weekend's annual Big Garden Birdwatch.
Households across the country are being asked to spare some time to count the different species they see, and pass the record on to the RSPB.
The annual count, which has been going since 1979, will reveal the most common winter bird.
The RSPB is hoping for an increase in overall numbers, despite some common species declining in recent years.
Nearly 400,000 people around the UK took part in the survey last year, observing 6 million birds in 200,000 gardens.
Jane Sellek from the RSPB said the survey would help them understand what is affecting bird populations.
"It's really important for the RSPB because it helps us monitor whether species are declining or alternatively if they're actually increasing. And particularly with climate change gathering speed we want to know obviously if that's affecting the bird populations," she said.
Project co-ordinator Richard Bashford said that, although there is now less woodland in the UK than in the past, birds have adapted.
"Gardens have a lot of cover and, of course, lots of people feed birds so birds are cottoning on to the fact that gardens are really good," he told BBC News.
"There's shelter, there's food, there's water, so quite a lot of these things are moving from the countryside to where we live.
"It's really good news because you can see wildlife very close to us."
But, despite this, he said many of the common species were in decline.
The house sparrow was the most common winter bird in 2005 with an average of 4.6 sparrows seen per garden.
This compares with an average of 10 per garden in 1979.
To take part in the Big Garden Birdwatch, watchers are invited to spend one hour over the weekend counting the birds in their garden or local park.
They should record the highest number of each species seen at any one time.
An online survey form together with more details can be found on the RSPB website.