Figure S1 | Recorder effort in 2016 from different data sources. (a) GBIF recorder effort; (b) iNaturalist recorder effort; (c) Flickr recorder effort; (d) Instagram recorder effort. Recorder effort was calculated as the abundance of blackbirds in a cell as reported by that data source divided by the actual estimated abundance according to data from the European Breeding Bird Atlas36. Grid size is approximately 50 km2, although some gird cells varied in size. Grid was supplied by European Breeding Bird Atlas.