Bird lovers in Wales are being asked to turn their binoculars closer to home over the weekend.
Sparrows are the most commonly seen birds in Welsh gardens
The Royal Society for the Protection of Birds Cymru is holding its 25th annual count of garden birds - the largest bird survey in the world.
Events are planned across the country to mark the event, with the RSPB visiting the Centre for Alternative Technology in Machynlleth during the count.
Last year, 15,000 people from Wales took part in the survey and the charity is hoping even more will get involved this time.
In 2003, the most commonly-seen bird was the house sparrow, with an average sighting of 5.4 per garden in Wales.
The survey began in 1979 and asks people to spend an hour either in their garden or a local park recording the highest number of bird species seen at one time.
Ruth Billingham from RSPB Cymru said: "Its an incredible achievement for a survey to reach it's 25th birthday.
"We are amazed at how the popularity of Big Garden Birdwatch has grown over the years.
She said there was a serious side to the event. "Numbers of many familiar garden birds are falling.
"It was the Big Garden Birdwatch that first pointed to many of these declines.
"The song thrush, which was once common has now disappeared from the UK top ten and the average number of starlings seen in gardens, has plummeted from 15 in 1979 to just four in our most recent survey."