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.