Effects of Sublethal, Cerebral X-Irradiation on Movement and Home-Range Patterns of Black-Tailed Jackrabbits
Abstract
Effects of sublethal, cerebral irradiation on movement and home-range patterns of black-tailed jackrabbits were studied in Curlew Valley, Utah, using radio-telemetry. Irradiation of 70 captive animals indicated that the LD50(30) was between 5,556 and 6,200 roentgens.
Nine wild, free-living experimentals were trapped in desert terrain, irradiated, transmittered, and released at the capture sites. Seven wild controls were treated similarly but were not irradiated. The field-irradiation dosage was 5,000 roentgens.
Tracking accuracy was determined by telemetering transmitters at fixed locations. Mean hourly movement was measured within 20-30 percent error and home ranges were measured with an error of less than 22 percent.
Experimentals had a mean hourly movement of 1,176,8 feet and controls 980.0 feet, significantly different at the .05 probability level. Experimentals had a bimodal activity curve with peaks at 5:00 p.m. and 3:00 to 5:00 or 6:00 a.m. Controls displayed no such pattern.
Experimentals had a mean, daily home range of 66.1 acres and controls 34,1 acres, significantly different at the .05 probability level. Experimentals had a seasonal home range of 279.0 acres and controls 247.0 acres, not significantly different at the .05 probability level.
A probability index showing the frequency distribution of each animal's activity within 300-foot concentric, circular bands around a geometric center of activity showed similar distributions for both groups. The greatest concentrations of activity were within the innermost band for each group but experimentals had a slightly greater scatter of points in the outermost zone. These distributions were not significantly different at the .05 probability level.
Sublethal, cerebral irradiation appears to have increased activity levels of experimental animals but not changed those home-range characteristics involving the total area occupied and tenacity of site attachment. This increased activity may have resulted from inhibitory areas in the cortex which permitted greater expression of activity from the limbic system.