Over 19 million records were submitted to the atlas, of which approximately 16 million were used in the production of the book. These records came from over 182,000 Timed Tetrad Visits, 3.8 million Roving Records and 4.5 million BirdTrack records. The majority of these records were submitted by over 17,000 observers using the BirdAtlas and BirdTrack websites. Additionally, records were sourced from BTO and BirdWatch Ireland surveys and projects, Bird Clubs archives and data from NGOs and species specialist groups. The figure below indicates the main data sources incorporated into the Atlas. In total data were sourced from approximately 40,000 observers.