Observations of American Crows (Corvus brachyrhynchos) during nocturnal roosting in downtown Portland, Oregon: Quantity, density, and distribution over time

Rural roosts in excess of 100,000 American Crows have been documented in North America since the early 1800s. Within the past 50-60 years roosts numbering in the tens of thousands have become increasingly common in urban areas. However, despite the long documented history of such roosts, no studies have been found documenting the behavioral details of crow roosts across time. In Portland, Oregon, anecdotal reports of crows roosting in the downtown area began within the past decade. In January 2018 a systematic observation of the Portland Crow Roost was done with the initial goal to create a time-series record of roost behavior, followed by goals of educating citizens and scientists about urban roost dynamics, and ultimately fostering appreciation of the phenomenon and reducing perceived crow-human conflicts. Approximately one square mile of the downtown area, covering 13 miles of gridded streets, was regularly surveyed in order to conduct a census and record the density and locations of roosting birds. Counts were done with a modified double-sampling estimating method by one or two observers. A total of 47 surveys were completed between January 6, and December 28, 2018. The highest census was 13,740 on Dec. 28. Of the approximately 300 blocks within the survey area, crows were found to have roosted on over 100 of the blocks at some point during the year.