Coyote responses to changing jackrabbit abundance affect sheep predation

Authors

L. Charles Stoddart, Utah State University, Logan, UT
Richard E. Griffiths, Utah State University, Logan, UT
Frederick F. Knowlton, Utah State University, Logan, UTFollow

Document Type

Article

Date of this Version

January 2001

Comments

Published by J. Range Manage. 54: 15–20 January 2001.

Abstract

Domestic sheep ranchers generally perceive abundances of natural prey and coyotes (Canis latrans) as important factors affecting coyote predation rates on sheep. To determine the effect of a changing natural prey base on coyote predation rates, we estimated coyote density and predation rates on ewes and lambs during part of 1 cycle of black-tailed jackrabbit (Lepus californicus) abundance on a 2,300 km² area of the Idaho National Engineering Laboratory in south-central Idaho from 1979–1985. We used 100, 1.6-km scat collection lines and 80, 1.6-km flushing transects to assess coyote and jackrabbit densities, respectively. Ewe and lamb loss rates were determined from questionnaires sent to all 13 producers grazing sheep on the area. Spring coyote density varied from 0.10 to 1.39 coyotes km^-2 in response to a systematic fluctuation in jackrabbit density from 0 to 243 jackrabbits km^-2. Reported total loss rates of ewes and lambs varied from 2.2 to 42.1 ewes/10⁵ ewe-days and 33.0 to 163 lambs/10⁵ lamb-days and were linearly and directly related to coyote density (P < 0.005). Ewe and lamb loss rates were independent of jackrabbit density (P > 0.18) except for 1 year when jackrabbits were virtually absent from the study area and the loss of lambs escalated dramatically. Our data suggest the increased losses of lambs resulted from reduced buffering by natural prey.