Diurnal roost site characteristics of northern Saw-whet Owls wintering at Assateague Island, Maryland

We characterized 30 diurnal roost sites of five radio-tagged Northern Saw-whet Owls (Aegolius acadicus) in the winters of 1996-1997 on Assateague island, Maryland and found they preferred thick cover at roost sites. Roosts occurred most often in loblolly pine forest (Pinus taeda) and shrub swamps dominated by wax myrtle (Myrica cerifera). Vegetation was measured at paired roosts and random sites in similar habitats. Distance to nearest tree and average canopy height were significantly lower at roost sites than random sites. Numbers of stems larger than 2.5 cm diameter at breast height (dbh), stems smaller than 2.5 cm dbh, and roost tree dbh were larger at roost sites. Roost height, canopy cover, canopy height, shrub height, and ground cover differed significantly between pine and shrub swamp roosts, although cover above and below the roost site were simile. Higher densities of stems and shorter distances to the nearest tree at roost sites compared to random sites indicated that owls chose sites with dense cover, probably as protection from predators or weather.