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Breeding Time In A Migratory Songbird Is Predicted By Drought Severity And Group Size, Charles R. Brown, Mary Bomberger Brown

School of Natural Resources: Faculty Publications

Global climate change is altering the breeding phenology of many organisms, and one reported consequence of warmer average temperatures is earlier breeding times in migratory songbirds of north temperate latitudes. Less studied are the potential interactions between earlier breeding and social behavior in colonial species. We investigated how breeding time, as measured by colony initiation dates across the entire summer, in Cliff Swallows (Petrochelidon pyrrhonota) of southwestern Nebraska, USA, changed over a 30-year period and could be predicted by climatic variables, year, and colony size. Mean colony initiation date became earlier over the study, with variation best predicted …

Atrazine And Nitrate In Public Drinking Water Supplies And Non-Hodgkin Lymphoma In Nebraska, Usa, Martha G. Rhoades, Jane L. Meza, Cheryl L. Beseler, Patrick J. Shea, Andy Kahle, Julie M. Vose, Kent M. Eskridge, Roy F. Spalding

School of Natural Resources: Faculty Publications

A secondary analysis of 1999–2002 Nebraska case-control data was conducted to assess the risk of non-Hodgkin lymphoma (NHL) associated with exposure to nitrate- and atrazine-contaminated drinking water. Water chemistry data were collected and weighted by well contribution and proximity of residence to water supply, followed by logistic regression to determine odds ratios (OR) and 95% confidence intervals (CI). We found no association between NHL risk and exposure to drinking water containing atrazine or nitrate alone. Risk associated with the interaction of nitrate and atrazine in drinking water was elevated (OR, 2.5; CI, 1.0–6.2). Risk of indolent B-cell lymphoma was higher …

Tracking Large Carnivore Dispersal Using Isotopic Clues In Claws: An Application To Cougars Across The Great Plains, Viviane Hénaux, Larkin A. Powell, Keith A. Hobson, Clayton Kent Nielsen, Michelle A. Larue

School of Natural Resources: Faculty Publications

1. Cougar (Puma concolor) populations, like other large carnivores, have increased during recent decades and may be recolonizing their former ranges in Midwestern North America. The dispersal routes taken by these animals from established populations are unknown and insight into these movements would facilitate their conservation and management.

2. We inferred the origin and migration route of four dispersing cougars using stable hydrogen (δD) and carbon (δ¹³C) isotope values along one of their claws. We compared isotopic variations within claws to regional and large-scale isoscapes of δD and δ¹³C values in prey species. Using …

Optimizing Allocation Of Monitoring Effort Under Economic And Observational Constraints, Scott A. Field, Andrew J. Tyre, Hugh P. Possingham

School of Natural Resources: Faculty Publications

Efforts to design monitoring regimes capable of detecting population trends can be thwarted by observational and economic constraints inherent to most biological surveys. Ensuring that limited resources are allocated efficiently requires evaluation of statistical power for alternative survey designs. We simulated the process of data collection on a landscape, where we initiated declines over 3 sample periods in species of varying prevalence and detectability. Changing occupancy levels were estimated using a technique that accounted for effects of false-negative errors on survey data. Declines were identified within a frequentist statistical framework, but the significance level was set at an optimal level …

The Relative Importance Of Patch Area And Perimeter–Area Ratio To Grassland Breeding Birds, Christopher J. Helzer, Dennis E. Jelinski

School of Natural Resources: Faculty Publications

Habitat fragmentation has been implicated as a major cause of population decline in grassland birds. We tested the hypothesis that a combination of area and shape determines the use of grassland patches by breeding birds. We compared both species richness and individual species presence in 45 wet meadow grasslands in the floodplain of the central Platte River, Nebraska. Bird data were collected through the use of belt transects and supplemented by walking and listening outside transects. Our data supported our primary hypothesis that perimeter–area ratio, which reflects both the area and shape of a patch, is the strongest predictor of …