A premigratory flock of Swainson's Hawks numbering at least 213 individuals was observed during July and August of 1984. Aerial feeding on grasshoppers was noted and kleptoparasitism was recorded between the Swainson's Hawk and the American Kestrel.
Woffinden, Neil D.
"Notes on the Swainson's Hawk in central Utah: insectivory, premigratory aggregations, and kleptoparasitism,"
Great Basin Naturalist: Vol. 46
, Article 21.
Available at: http://scholarsarchive.byu.edu/gbn/vol46/iss2/21