• Feral Horse Demography: A Preliminary Report

      Wolfe, M. L. (Society for Range Management, 1980-09-01)
      The demographic characteristics of 18 feral horse (Equus caballus) populations in five states are discussed. As estimated primarily from the results of composition counts, foals comprised an average 19 percent (post-parturition) of the populations analyzed. Various procedures were employed in an attempt to estimate survival rates within the populations. Provisional estimates of first-year survival rates span the general range of 50-70 percent, while those for adults may approximate 80-85 percent. Annual rates of increase, predicted from simulation runs with the estimated population parameters, were considerably lower than those "observed" from aerial inventories in successive years. Possible explanations for these discrepancies and management implications are discussed.
    • Range Improvement Practices and Ferruginous Hawks

      Howard, R. P.; Wolfe, M. L. (Society for Range Management, 1976-01-01)
      The implications of range improvement practices on ferruginous hawks (Buteo regalis) are discussed. During 1972 and 1973 the habitat requirements and breeding biology of 43 and 54 nesting pairs, respectively, were studied in northern Utah and southeastern Idaho. Utah juniper (Juniperus osteosperma) provided sites for 95% of observed nests. Desert shrub types and crested wheatgrass (Agropyron cristatum) seedings comprised the dominant vegetation around nest sites. Black-tailed jackrabbits (Lepus californicus) comprised 88.7 and 79.4% (by weight) of prey items collected from nests in the 2 years of study. Jackrabbit abundance may be a major determinant of the raptors' reproductive success in a given year, as suggested by a 47% decline in the number of young fledged per occupied territory between 1972 and 1973, concurrent with an estimated 79% decrease in jackrabbit numbers. Suggestions for minimizing or ameliorating the impact of range improvement practices on the hawks' prey base are given.