Traditional atlases are out of date? How online platforms can help when the resources available are scarce

Abstract

Time has changed, online portals for biodiversity, and for birds in particular, are widespread and respon- sible for collecting millions of records annually around the world. This has multiple implications on the data availability and quality. On one side we have huge up-to-date datasets to be analysed, but on the other side, concerns about data quality and data standardization are common. Can part of this data be used to improve atlas design and make the most of the few resources available? Are the future atlases ongoing works that only need censuses in low surveyed areas from time to time? To evaluate the po- tential of eBird data to plan a wintering atlas for Continental Portugal we analysed eight years of data (2013–2020 winters), focusing on the coverage of the country at ETRS 10 × 10 km, using as minimal sampling effort ten complete checklists and at least 3 h of census (identical to the first national wintering atlas). From the c. 1,000 squares 946 had at least one checklist for this period and 465 (~49%) had records in 6 years provided by 1,666 different observers. Additionally, 685 squares (~68%) had more than 3 h of surveys; by overlapping these maps we were able to identify not only low coverage areas (e.g. south west part of the country, the mountain areas) but also specific squares. These results, to- gether with the number of species detected by square, and compared with the results of the first winter- ing atlas (2011–2012) provide a useful tool to efficiently plan future atlas.