Identifying Communal Crow Roost Dynamics and Transitions through Citizen Science

American crows ( Corvus brachyrhynchos ) form large, nightly communal roosts of 100s to 100,000s of individuals throughout the non-breeding season. Obtaining comparable estimates of their numbers facilitates monitoring and understanding of roost dynamics. We describe a simple counting method that utilizes citizen scientists to produce annual estimates of crows using a large communal roost in Bothell, WA. Over the last ten years, volunteers have counted crows during their pre-roost approach at multiple flyover locations predictable in space and time. Observed changes in the number of crows led to the discovery of a spontaneous roost dissolution (i.e., not intentionally caused by humans), ephemeral roosting sites, and two newly formed, longer-term communal roosts. Similar citizen scientist-based approaches can be applied at other sites to better assess and understand the general dynamics of avian roosting behavior and build public awareness of and connection with urban wildlife.