Big Garden Birdwatch, organised by the RSPB, aims to find out which species are the most common visitors to UK gardens in the winter.

Nearly 400,000 people nationwide took part in last year's survey and six million birds were recorded from surveys in more than 200,000 gardens.

An RSPB Yorkshire spokesman said fewer varieties are being reported.

Those taking part are asked to watch their gardens or local park for an hour this weekend and record what birds are seen and then tell the RSPB the highest number of each species that are seen at any one time in the hour.