Roger Sayre

Date of Award

7-9-1997

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Robert Seabloom

Abstract

I conducted field research on bighorn sheep (Ovis canadensis californiana) in western North Dakota to evaluate their distribution, habitat use, activity patterns, and responses to disturbance. The study was conducted May-December from 1992-94, at Magpie Creek, an area with a high density of roads and oil wells, and Moody Plateau, with a low density of roads and oil wells.Radio-collared ewes (n = 8) at Magpie Creek used steep non-vegetated terrain more than available during summer, but less than available during fall. They used closed juniper areas less than available during summer and fall, but used disturbed habitats more than available during both seasons. Home ranges were larger during fall compared to summer. The sheep at Magpie Creek have not abandoned their traditional home range after implementation of oil wells, and tend to use the same core area as their ancestors--animals that were maintained in an enclosure from 1956-66.Vehicles (0.16 incidents/hour) and coyotes (0.04 incidents/hour) were the most frequent disturbances observed at Magpie Creek, whereas disturbances from low-flying military jets (0.12 incidents/hour) and vehicles (0.05 incidents/hour) were observed most frequently at Moody Plateau. Sheep responded more strongly to vehicles or aircraft that flew $\le$200 m than those that flew $>$200 m. Foraging efficiency declined after incidental disturbances.Radio-collared ewes (n = 7 at Magpie Creek and n = 5 at Moody Plateau) exhibited diurnal activity patterns, with peak activity occurring 1 or 2 hours after sunrise and during late afternoon. The animals tended to remain relatively inactive at night, although during fall activity levels approached or exceeded 20% at midnight ($\pm$1 hour). Sheep at Magpie Creek exhibited decreased activity levels on oil-well maintenance days during summer, and they increased morning and evening activity levels on hot ($\ge$30 C) days.Fecal cortisol levels of ewes at Magpie Creek (n = 8) and Moody Plateau (n = 7) followed a significant seasonal pattern with peaks during June-July, and during late pregnancy, from January-April. Fecal cortisol was higher at Moody Plateau than Magpie Creek during late summer and fall. Cortisol levels of n = 10 ewes increased by 82% after opening weekend of deer rifle season.

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