Pre-Roosting Assemblages in Birds: An Observation of American Crows in the Portland Park Blocks

Abstract

The first objective of this study is to describe the seasonal patterns of variation in crow numbers and to assess the extent to which crow numbers vary with weather over the course of the winter in the Portland State University Park Blocks. The second objective of this study is to draw on current literature to help determine a possible explanation for the crow gatherings that occur at the Portland State University Park Blocks. I observed the population of crows from October 23 2016 to March 31 2016 with a restricted survey area around Millar Library on the Portland State University Campus and Market St (a five block area). I made observations two days a week for periods lasting between 1.25 and 3 hours, while making both qualitative and quantitative observations of crow numbers and activity. Seasonal variation of crows in the Park Blocks on PSU campus increased from mid-fall into the winter season in a non-linear fashion. Weather influenced flocking behavior as crow numbers exhibited a weak tendency to peak at intermediate values of precipitation and to increase with wind speed. This study can serve as a base for the future work to help explain why American Crows use communal roosts during the winter months. Pre-Roosting Assemblages in Birds 3