Global Ecol Biogeogr. 2019;1–9. wileyonlinelibrary.com/journal/geb | 1 © 2019 John Wiley & Sons Ltd Received: 7 August 2018 | Revised: 15 January 2019 | Accepted: 22 January 2019 DOI: 10.1111/geb.12906 DATA PAPER Breeding and wintering bird distributions in Britain and Ireland from citizen science bird atlases Simon Gillings 1 | Dawn E. Balmer 1 | Brian J. Caffrey 2 | Iain S. Downie 3 | David W. Gibbons 4,5 | Peter C. Lack 1 | James B. Reid 6 | J. Tim R. Sharrock 7 | Robert L. Swann 8 | Robert J. Fuller 1 1 British Trust for Ornithology, Thetford, United Kingdom 2 BirdWatch Ireland, Banagher, Ireland 3 Coventry, United Kingdom 4 RSPB Centre for Conservation Science, Sandy, United Kingdom 5 RSPB Centre for Conservation Science, Cambridge, United Kingdom 6 Crail, United Kingdom 7 Blunham, United Kingdom 8 Tain, United Kingdom Correspondence Simon Gillings, British Trust for Ornithology, The Nunnery, Thetford, Norfolk IP24 2PU, United Kingdom. Email: simon.gillings@bto.org Editor: Erica Fleishman Abstract Motivation: We undertook large citizen science surveys of bird distributions (atlases) in Britain and Ireland, aimed at quantifying breeding bird distributions on a 20‐year cycle and wintering bird distributions on a c. 30‐year cycle. We use these to generate spatially referenced information on apparent changes in bird distributions over c. 40 years. Main type of variable contained: Detection of breeding and wintering bird species in grid squares during five periods, and changes in detection between periods. The combined distribution dataset contains 1,410,938 records detailing detections of 465 bird species in 3,880 grid cells in different periods. The combined distribution change dataset contains 1,297,791 records describing stability, apparent colonization or ap‐ parent extinction of individual species in grid squares between pairs of atlases span‐ ning up to c. 40 years. Spatial location and grain: Grid squares (10 km × 10 km) containing land throughout Britain, Ireland, the Isle of Man and the Channel Islands. The majority of data are at 10‐km resolution, but data for rare species are summarized at 20‐ or 50‐km resolu‐ tion to protect sensitive locations. Time period: The data represent summarized detection information derived from fieldwork during five periods: the breeding seasons 1968–1972, 1988–1991 and 2008–2011, and the winters 1981/1982–1983/1984 and 2007/2008–2010/2011. Major taxa studied and level of measurement: Birds; their distribution derived from citizen science surveys. Software format: Data are supplied as comma‐separated text files. KEYWORDS birds, Britain, citizen science, distribution change, geographical distribution, historical distributions, Ireland