In birds, fine-scale selection of habitat, like roosting sites, plays an important role in energy conservation. Many diurnal birds roost in cavities or densely foliated coniferous trees, both of which may provide shelter from predators and precipitation, and reduce heat loss from convective and radiative forces. Thermal benefits of roost sites have not been widely studied in nocturnal birds, like owls, roosting during the day. The objective of this study was to assess possible thermal benefits of coniferous roosting sites for the small, nocturnal Northern Saw-whet Owl (Aegolius acadicus) at the southern extent of its nonbreeding distribution, where winters are often mild with warm days. I deployed operative temperature models (n = 40) for 21 d at 10 sites in Madison County, Arkansas. Sites were either a shortleaf pine (Pinus echinata) or eastern red cedar (Juniperus virginiana) roost tree, each paired with a deciduous tree. At each site, I synchronously deployed models in 4 microsites reflecting potential owl roosting sites that likely varied considerably in their thermal properties: conifer crown, conifer trunk, deciduous crown, deciduous trunk. My objectives were to (1) test for an effect of microsite on 4 composite operative temperature variables, and (2) test for an effect of microsite on mean wind speed. Results suggest conifer crown roost sites are cooler, more thermally buffered, and experience lower wind speed than deciduous crown and both trunk roost sites. Thus, the saw-whet owl likely benefits from overwintering in coniferous trees to avoid thermally stressful temperatures, particularly on warm winter days.

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