“…Moreover, such observations allow to monitor migratory birds, e.g., [ 30 , 31 , 32 , 33 , 34 ]; rare and endangered species, e.g., [ 35 , 36 , 37 , 38 ]; expansion of pests, e.g., [ 20 , 39 , 40 ]; or alien and/or invasive species, e.g., [ 18 , 22 , 39 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ] as well as colonization of new human-made habitats, e.g., [ 51 ]. In addition, numerous studies show that data collected by amateur scientists allow to describe new interactions between species, e.g., [ 17 , 52 ], to investigate animal phenology, e.g., [ 53 ], and behavior, e.g., [ 54 ], to find changes in species abundance and demography, e.g., [ 55 , 56 , 57 ], and other threats for local fauna and flora being important for nature conservation, e.g., [ 8 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 ].…”