Raptor and Vole Populations at an Airport

Abstract

Changes in numbers among overwintering populations of 4 species of raptors were studied in relation to changes in abundance of meadow voles (Microtus pennsylvanicus) on Toronto International Airport from October to April of 1974-75 and 1975-76. Data from small-mammal trapping, analysis of raptor pellets, and direct observations of prey hunted and captured by the raptors indicated that meadow voles were the major prey of all 4 raptor species. Rough-legged hawks (Buteo lagopus) and short-eared owls (Asio flammeus) exhibited a greater numerical response to changes in vole abundance than did redtailed hawks (Buteojamaicensis). Changes in snowy owl (Nyctea scandiaca) numbers were opposite those of the other raptors. J. WILDL. MANAGE. 45(2):390-396 Birds may create a serious hazard for aircraft, and considerable effort has been expended on developing effective methods of reducing bird populations at airports (Blokpoel 1976). More basic information is required if accurate predictions of how bird populations respond to various control procedures are to be derived. On Toronto International Airport, 4 species of raptors (red-tailed hawk, rough-legged hawk, snowy owl, shorteared owl) are common winter residents. Frequently these raptors become abundant and create hazards for aircraft traffic. Previous control measures, including shooting and livetrapping, have had limited success in reducing raptor numbers on the airport. Our study was undertaken to develop a management program that would reduce the raptor population of the airport. The objectives were to determine the prey used by the 4 raptor species, the response of these raptors to changes in prey abundance, and other variables that may cause changes in raptor abundance. We thank R. W. Steele for use of his data; A. L. A. Middleton and D. E. Joyner for comments on the manuscript; W. King, S. Lane, and G. Nancekivell for technical assistance; and E. B. Hartwick for initial supervision of the project. Special thanks are expressed to U. Waterman, J. A. Mason, and airport personnel.