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International and Area Studies
University of Nebraska - Lincoln
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Articles 1 - 3 of 3
Full-Text Articles in Social and Behavioral Sciences
Interpreting Carnivore Scent-Station Surveys, Glen A. Sargeant, Douglas H. Johnson, William E. Berg
Interpreting Carnivore Scent-Station Surveys, Glen A. Sargeant, Douglas H. Johnson, William E. Berg
USGS Northern Prairie Wildlife Research Center
The scent-station survey method has been widely used to estimate trends in carnivore abundance. However, statistical properties of scent-station data are poorly understood, and the relation between scent- station indices and carnivore abundance has not been adequately evaluated. We assessed properties of scent- station indices by analyzing data collected in Minnesota during 1986-93. Visits to stations separated by < 2 km were correlated for all species because individual carnivores sometimes visited several stations in succession. Thus, visits to stations had an intractable statistical distribution. Dichotomizing results for lines of 10 stations (0 or ≥ 1 visits) produced binomially distributed data that were robust to multiple visits by individuals. We abandoned 2-way comparisons among years in favor of tests for population trend, which are less susceptible to bias, and analyzed results separately for biogeographic sections of Minnesota because trends differed among sections. Before drawing inferences about carnivore population trends, we reevaluated published validation experiments. Results implicated low statistical power and confounding as possible explanations for equivocal or conflicting results of validation efforts. Long-term trends in visitation rates probably reflect real changes in populations, but poor spatial and temporal resolution, susceptibility to confounding, and low statistical power limit the usefulness of this survey method.
Mallard Duckling Growth And Survival In Relation To Aquatic Invertebrates, Robert R. Cox, Mark A. Hanson, Christianne C. Roy, Ned H. Euliss Jr., Douglas H. Johnson, Malcolm G. Butler
Mallard Duckling Growth And Survival In Relation To Aquatic Invertebrates, Robert R. Cox, Mark A. Hanson, Christianne C. Roy, Ned H. Euliss Jr., Douglas H. Johnson, Malcolm G. Butler
USGS Northern Prairie Wildlife Research Center
Identification and assessment of the relative importance of factors affecting duckling growth and survival are essential for effective management of mallards on breeding areas. For each of 3 years (1993-95), we placed Fl-generation wild mallard (Anas platyrhynchos) females on experimental wetlands and allowed them to mate, nest, and rear broods for 17 days. We manipulated invertebrate densities by introducing fathead minnows (Pimephales promelas) at high densities in half of the wetlands on which broods were confined. Day- 17 body mass of surviving ducklings (n = 183) was greater for ducklings that were heavier at hatch; the …
Checklist And ‘‘Pollard Walk’’ Butterfly Survey Methods On Public Lands, Ronald Royer, Jane Austin, Wesley Newton
Checklist And ‘‘Pollard Walk’’ Butterfly Survey Methods On Public Lands, Ronald Royer, Jane Austin, Wesley Newton
USGS Northern Prairie Wildlife Research Center
Checklist and ‘‘Pollard Walk’’ butterfly survey methods were contemporaneously applied to seven public sites in North Dakota during the summer of 1995. Results were compared for effect of method and site on total number of butterflies and total number of species detected per hour. Checklist searching produced significantly more butterfly detections per hour than Pollard Walks at all sites. Number of species detected per hour did not differ significantly either among sites or between methods. Many species were detected by only one method, and at most sites generalist and invader species were more likely to be observed during checklist searches …