R.R. Ramey | Geology Reports

USGS2001

Genetic bottlenecks resulting from restoration efforts: The case of bighorn sheep in Badlands National Park

Using the example of a reintroduced bighorn sheep population in Badlands National Park, South Dakota we demonstrate the usefulness of neutrality tests and demographic data for detecting a severe genetic bottleneck (Ne < 10). From demographic data the effective population size of the founding population at Badlands was estimated to be six, and a heterozygosity excess test revealed evidence of a severe population bottleneck. We discuss the criteria for intervention when there is evidence of a severe bottleneck, and propose methods of mitigating the potentially deleterious long-term consequences of such bottlenecks. These issues are presented in the context of bighorn sheep reintroductions, but the issues are also of general importance to restoration efforts involving other large vertebrates.

South Dakota↗

USGS1986

Nest-site biology of the California condor

A study of 72 historical and recent nests of the California Condor (Gymnogyps californianus) has revealed considerable variability in nest-site characteristics. This paper primarily summarizes the data on nest elevations and dimensions, entrance orientations, nest longevity and re-use, vulnerability of sites to natural enemies, and use of sites by other species. Although all known nests have been natural cavities, some have been little more than overhung ledges on cliffs, while others have been deep, dark caves with nest chambers completely concealed from the outside. Two sites have been cavities in giant sequoias (Sequoiadendron giganteum). Contrary to previous assumptions, condors do modify the characteristics of their nest sites significantly and commonly construct substrates of coarse gravel on which to rest their eggs. Many nests have been completely accessible to terrestrial predators, many have been poorly protected from avian predators, and some have had structural flaws leading directly to nesting failure. The use of suboptimal sites has not been clearly related to a scarcity of better quality sites.

Condor↗