THERMAL REGIMES OF MEXICAN SPOTTED OWL NEST STANDS

Abstract

To evaluate the hypothesis that spotted owls (Strix occidentalis) select habitats with cool microclimates to avoid high daytime temperatures, I sampled thermal regimes in nest areas used by Mexican spotted owls (S. o. lucida) in northern Arizona. I sampled air temperature at 30-min intervals in 30 pairs of nest and random sites from May through August and used the resulting thermal profiles to estimate a suite of diurnal temperature parameters. I estimated diurnal energy use and evaporative water loss, and compared these estimates and temperature parameters between nest and random areas. Owl nest areas were significantly cooler than random areas, and estimated evaporative water loss was significantly lower in nest areas than in random areas. In contrast, there was little difference in estimated diurnal energy use between nest and random areas. These results support the hypothesis that Mexican spotted owls select cool habitats. Use of these cooler habitats apparently reduces diurnal evaporative water loss relative to random areas, suggesting that water balance might be more important in habitat selection by spotted owls than previously realized. However, selection of cool nest areas apparently does not result in large energy savings, at least in this high-elevation study area (mean elevation at nest areas in this study was 2,230 m).