GRASS snakes and slow worms will be added to the world’s largest garden wildlife survey later this month.

More than half a million people are expected to watch and count their garden birds for this year’s RSPB Big Garden Birdwatch on January 24 and 25, with some surprising new creatures on the list.

The survey, now in its 36th year, provides information about the changes in numbers of birds using our gardens in winter, and helps to alert conservationists to those species in decline like house sparrows, greenfinches and starlings.

Last year, for the first time, the RSPB asked participants to log some of the other wildlife they see in their gardens to help build an overall picture of how important our gardens are for giving wildlife a home.

Now, for the next wildlife survey, slow worms and grass snakes have been added to the list.

Participants don’t have to see and count these other species during their Big Garden Birdwatch hour, just fill in the form to tell the RSPB whether they have ever seen them in their gardens, at any time of year.

It’s not always possible to survey other animals in the same way as birds, as they tend to be more secretive, nocturnal, less numerous or hibernating at the time the survey is carried out. But this way the charity can find out whereabouts in the country these creatures appear and how frequently.

The RSPB will share the results with conservation partners such as Amphibian and Reptile Conservation (ARC), People’s Trust for Endangered Species (PTES) and The Mammal Society.

The survey is part of the RSPB’s Giving Nature a Home campaign, aimed at tackling the housing crisis facing the UK’s threatened wildlife. The charity is asking people to provide a place for wildlife in their own gardens and outside spaces – by planting pollen-rich plants to attract bees and butterflies, putting up a nestbox for a house sparrow, or creating a pond that will support a number of different species.

Daniel Hayhow, RSPB conservation scientist, said: “This massive survey shows how important our gardens are for the amazing variety of wildlife living there.

“Adding slow worms and grass snakes to this year’s survey is a big step towards capturing more data, which will help us and our partners identify how the distribution of garden wildlife may have changed amongst a variety of species in a few years’ time.

“Hopefully, the fact that more people are helping to give nature a home in their gardens and outside spaces will mean we see improvements rather than declines.”

To take part in Big Garden Birdwatch 2015, register at rspb.org.uk/birdwatch

Last year's top 20 were:

1 House sparrow

2 Blue tit

3 Starling

4 Blackbird

5 Woodpigeon

6 Chaffinch

7 Goldfinch

8 Great tit

9 Collared dove

10 Robin

11 Magpie

12 Dunnock

13 Long-tailed tit

14 Feral pigeon

15 Greenfinch

16 Jackdaw

17 Coal tit

18 Carrion crow

19 Wren

20 Great spotted woodpecker