September 25 Biology Seminar
Speaker: Dr. David Schimpf, Assoc. Professor Emeritus, UMD Department of Biology
All Together Now: Hawk Ridge and the Harrier-Vole System
Abstract
North America's Northern Harrier (Circus cyaneus hudsonius) has been shown to have local population sizes that
track large year-to-year changes in abundance of Meadow Vole (Microtus pennsylvanicus), a prey species, in
Harrier breeding areas. Many Vole populations show local cycles of density, with high numbers every 4 or 5
years. Interannual differences in the observed numbers of migrating Harriers have been attributed to these periodic
swings in prey numbers, but formal evidence of this has not been published. Time-series analysis of Harrier counts
at autumn migration watch points in eastern North America found stronger evidence of cyclic changes closer to the
center of the continent. This suggests stronger synchronization of Vole cycles over broad geographic scale in
regions where snow cover is more persistent. Hawk Ridge Bird Observatory in Duluth plays a crucial role in this
finding.