Householders make observations from October to March inclusive, with the maximum number of each species seen using food or water provided (or observed hunting the birds that are using these resources) recorded on a weekly basis. Birds that are seen in gardens but do not use these human-provided resources are not recorded, unlike in the BTO Garden BirdWatch survey.
The GBFS is restricted to approximately 250 gardens in each year and these are selected carefully from pre-existing participants in the larger year-round BTO Garden BirdWatch survey. Gardens are chosen to ensure good geographical coverage across the UK and an approximately equal split between rural and suburban gardens. Each year a few GBFS participants drop out and suitable replacement gardens are identified from among the membership of BTO Garden BirdWatch. The GBFS is a relatively small project so it is funded from BTO resources and, hence, no contribution to costs is required. However, this does mean that participation is limited to approximately 250 gardens each year.
What we can learn from 25 years of watching gardens
Exploring the value of a complete quarter-century of weekly garden bird observations from BTO's Garden BirdWatch covering the length and breadth of the country.