Contribution of citizen science towards cryptic species census: "many eyes" define wintering range of the Scaly-sided Merganser in mainland China

Background Citizen science has tremendous potential in advancing scientific knowledge and improving natural resource management. To detect the wintering distribution of the endangered species Scaly-sided Merganser (Mergus squamatus), national wintering surveys were organized by China Birdwatching Association.

Methods The surveys of M. squamatus were conducted in three successive winters from 2014 to 2016. A total of 2019 people from 102 organizations participated in the surveys. With three groups of 13 environmental variables, species distribution model for its wintering distribution of each year was developed using random forest. Schoener's D index was used to compare the distribution of M. squamatus in 3 years.

Results Totally, 441, 634 and 1138 individuals of M. squamatus were recorded in 2014, 2015 and 2016 respectively. Two main sites in Dabie Mountain and East Qinling mountains were verified and the wintering range of M. squamatus was defined. The wintering range was found to be highly identical for the 3 years.

Conclusions The highly overlapped distribution range among years suggested that the wintering range of M. squamatus was relatively stable. Well organized and coordinated citizen science can be used to define distribution range and improve species conservation.