The RSPB’s Big Garden Birdwatch is the world’s biggest bird survey and in 2009 will be celebrating its 30th anniversary. Over 400,00 people took part last year to help find out which birds are in need of the RSPB’s conservation work.

Back in 1979 the RSPB asked its junior members to count the birds in their back gardens over one weekend in January to give a snapshot of the birds that visited UK gardens. The idea was so successful that the survey has run every year since then.

More than 6 million birds have been counted over that time and it has given some interesting insights into the populations of British birds.

Although the house sparrow and starling have consistently been the top birds spotted the average number seen has fallen. Back in the 70s and 80s it was common to see groups of up to 15 sparrows and starlings in gardens – now you would be lucky to see 3 or 4.

Song thrushes also used to be a lot more common in the 70s but have fallen massively in the Birdwatch rankings and overall garden bird numbers have decreased by 20% in the last 4 years.

However, it’s not all bad news; some birds have increased in numbers such as the goldfinch which entered the top ten for the first time in 2008. This is probably due to people putting out more suitable food, such as Niger seed, for finches.

There are many things you can do to encourage birds into your garden and help reverse the declining population trend. Many natural food sources are in short supply so by providing bird tables and feeders you will encourage birds to visit your garden.

Nesting places are disappearing as old buildings are demolished and hedgerows are cut back. Place a number of nest boxes in your garden to attract different species. You can get bird boxes designed with particular species in mind such as sparrow flats designed for sparrows who like to nest in colonies.

You can also plant your garden to encourage birds. Shrubs are trees with berries as well as wild flowers will all provide food and shelter. And a pond or bird bath will be used by birds for bathing and drinking particularly in winter months when usual supplies may be frozen over.

If you want to take part in the Big Garden Birdwatch in 2009 then all you need to do is spend an hour counting the birds in your garden or local park. Make sure you find a quiet spot where you will not be disturbed and download the counting sheet from the RSPB website so that you can keep track of what you have seen.

If it is cold then make sure you wrap up warm and take a flask of hot tea or soup with you. A pair of binoculars and a bird guide book will help with identification.

Once all the bird counts have been submitted then the RSPB will work with scientists to look for patterns in bird numbers to help prioritize their conservation work.

Find out more about the Big Garden Birdwatch.