Figure 1

Comparison of the geographical locations of the citizen and expert observations in the summer of 2011. The blue xs indicate the locations of the citizen observations and the red plus signs (‘+’) indicate the pre-determined locations of the expert observation sites. The numbers of citizen and expert observations (in this order) are presented for each grey rectangle (dimension of one degree latitude and two degrees longitude) which together cover the whole dataset (approx. 59.5N 20E, 67.5N 32E). The white rectangles indicate the smaller areas used in the analysis (Area1 = 59.5N 22E, 60.5N 24E and Area2 = 59.5N 22E, 61.5N 26E).