| Abstrakt: |
Grassland habitat in the Northern Prairie region has been greatly reduced since historical times, and this decline has recently intensified due to conversion to agricultural row-crop production. Common Nighthawk nesting habitat includes grasslands and urban rooftops, but preliminary data indicate disproportionate use of urban sites as nesting habitat in southeastern South Dakota, suggesting that row-crop landscapes are ill-suited for nesting. Nighthawks are crepuscular insectivores and income breeders that reduce activity when weather is unfavorable for arthropod prey. Accordingly, we expect nighthawk occurrence on point counts to be influenced by weather (i.e., temperature, short-term temperature change, sky and wind conditions), temporal factors (i.e., moon phase, time before/since sunset, Julian Date), and other variables (i.e., site and noise level). Using urban point count data in generalized linear models with binomial distributions, I analyzed the interaction of nighthawk presence/absence (as a dependent variable) with all variables. The models yielded low interaction probability between presence/ absence and all variables tested. These preliminary data suggest little impact of weather or temporal variables on urban nighthawk activity, which contrasts with other Caprimulgids. Reasons for a different response in nighthawks compared to other Caprimulgids might include urban habitats or the crepuscular, rather than nocturnal, habits of nighthawks, both of which are unusual among Caprimulgids. Future modeling with larger sample sizes and including natural ground nest sites is needed to test whether weather and temporal factors might differentially affect nighthawk activity in urban versus natural nesting areas. [ABSTRACT FROM AUTHOR] |
