One of the world's largest wildlife surveys, "the big garden birdwatch" is being launched by the UK's Royal Society for the Protection of Birds.
The charity hopes that around half a million people will record the abundance of different bird species visiting their gardens and open spaces.
By asking members of the public to spend one hour this weekend spotting birds, the charity can identify those species in most need of help.
The survey is now in its 32nd year.
We expect more birds than ever to be recorded in big garden birdwatch 2011, and maybe more unusual species than other years.
This year it starts on Saturday 29 January.
The results will be particularly useful in helping conservationists understand how the coldest December since records began has affected garden bird numbers.
"The really cold weather began quite early in December, and this would have been when natural food sources became scarce," said Dr Mark Avery, the RSPB's director of conservation.
"By now, these birds could have been making the most of our hospitality for over a month, meaning even more unusual sightings this weekend."
In addition to our usual garden visitors such as blackbirds, blue tits and robins, the charity expects some unusual sightings in the survey, with increasing visits by less common birds such as waxwings.
Dr Avery said: "Regardless of where they live, or the size of their outside space, people in the UK have been united this winter in their wish to try and help garden birds."
You do not need to have a garden to take part. Participants are expected to join in from a wider variety of gardens and public open spaces, including parks.
The RSPB is asking people to download a form from its website and use it to record the highest number of every bird species seen at any one time.
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