Since fieldwork started in early 1968, bird atlases have been a periodic feature of the bird surveying landscape in Britain and Ireland. They have provided countless hours of enjoyment for their volunteer participants and yielded data crucial for conservation and research activities. BTO and our collaborators have been working with these data for many decades, but now BTO is taking the bold step of making the full archive of distribution data freely available for anyone to use, as described in a new ‘data paper’ published in the journal Global Ecology and Biogeography. The first breeding atlas – the first national bird atlas anywhere in the world - conducted during 1968–72, was described at the time as “a huge step forward in our knowledge of the distributions of British and Irish birds. It is by far the biggest co-operative effort ever undertaken by field ornithologists in these islands, indeed probably anywhere in the world, which will stand for many years as a tribute to the enthusiasm and industry of a large number of people”. Subsequent atlases have continued that theme, and collectively the series of breeding and wintering atlases from 1968–72 to 2007–11 contain 1.4 million 10-km resolution distribution records of 458 species. This new paper describes how fieldwork in the different atlases was conducted and how these records were collated to produce distribution and distribution change datasets. It explains some of the subtle changes in field methods, breeding evidence criteria, effort and taxonomy that impact how the data can be used. For example, in that pioneering 1968–72 breeding atlas fieldwork involved visiting 10-km squares and searching for breeding evidence and no counting of individual birds was required. By Bird Atlas 2007–11, volunteers were also undertaking timed visits in 2-km tetrads to provide a systematic estimate of relative abundance. The combined effort required to generate these atlases is very hard to estimate. Probably in excess of 60,000 volunteers contributed over 20 million bird records spanning 99.9% of the land area of Britain and Ireland. We are indebted to those volunteers for providing such a comprehensive picture of the changing status of the birds of Britain and Ireland. They will be reassured to know that although the majority of the data are provided at 10-km resolution, distributions for a minority of rare or sensitive species are shared at 20-km or 50-km resolution as mapped in the most recent atlas. BTO has already made distribution maps freely available via the Bird Atlas Mapstore. Now in making the underlying distribution and change data freely available (for non-commercial uses) we hope to facilitate new work on topics such as species distribution modelling, assessing the drivers of distribution change and forecasting the response of species to future environmental change and other innovative uses that have yet to be devised. Download the dataset This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License. The dataset can be downloaded here: https://zenodo.org/records/10599935

A study led by BTO, working with the Wetland Bird Survey (WeBS) partners, JNCC, RSPB and in association with WWT, provides detailed information on the importance of Great Britain for waterbirds each winter. The work gives revised population estimates for 98 different species that winter in Great Britain, using data collected by many thousand birdwatchers to calculate either the average peak winter population over a five year window between winters 2012/13 and 2016/17, or the most recent possible estimate. Overall, Britain is estimated to host 12.8 million individual waterbirds each winter. The results suggest that geese are doing well while waders are declining - the estimated total number of geese wintering in Britain increased by approximately 175,000 since the previous assessment eight years ago, but waders were down by approximately 142,000 birds. The upturn in geese was largely driven by an increase in Pink-footed Goose by 150,000 individuals, while the wader downturn encompasses falls in numbers of Knot, Oystercatcher, Redshank and Curlew. The study also produced estimates for Cattle Egret, Sandwich Tern and Glossy Ibis for the first time, as well as January-only estimates for 48 species, which are important because January is the focus of global waterbird monitoring via the International Waterbird Census. Waterbirds are a diverse group, and this work involved a range of methods and novel analytical techniques to generate the best possible estimates for each species. WeBS data were used for species commonly found on WeBS sites, such as Dark-bellied Brent Goose and Gadwall, along with extrapolation factors to compensate for birds on non-WeBS sites. For species that prefer the open coast, such as Turnstone, Purple Sandpiper and Great Northern Diver, observations from the Non-estuarine Waterbird Survey (NEWS III) were used. Importantly, this work developed statistical models to generate estimates for some of the most widespread species, for example Teal, that occur on small waterbodies often not routinely counted in WeBS and other surveys. This work summarises data gathered by thousands of birdwatchers across Great Britain, who spent a huge number of hours in the field. As well counts collected by 2,900 WeBS volunteers on WeBS Core Counts and supplementary visits, data gathered by the WWT/JNCC/SNH Goose & Swan Monitoring Programme (GSMP), 860 participants in the 2015/16 NEWS III survey and 600 participants in the BTO Heronries Census were used. More information extracted from specialist reports, BirdTrack and almost 100 county bird reports relied upon countless additional hours by many thousands of birdwatchers, county recorders and bird club committees to collect, digitise and summarise information on wetland birds. Thank you to everybody who contributed to this study – every record counts!