Characterizing Northern Saw-Whet Owl (Aegolius acadicus) Winter Habitats in South-Central Indiana

Northern Saw-whet Owl (Aegolius acadicus) winter habitat in south-central Indiana was assessed during two winters (2003/2004 & 2004/2005). Differences between locally occupied and unoccupied habitat were examined, and occupied habitat in Indiana was compared to occupied habitat in other regions. Using audio surveys and active voice detection, 40 locations were sampled in the first winter, 45 in the second winter, 35 in both winters and 50 total. The presence of Northern Saw-whet Owls was strongly related to the understory transparency, agreeing with previous studies in Maryland and Michigan showing a correlation with dense vertical structure. However, there was no evidence of a strong correlation between the presence of Northern Saw-whet Owls and either evergreen canopy cover, evergreen stem density or mid-canopy gap, contradicting results from other studies in Minnesota, Maryland and Michigan, though there was a minimum 40% evergreen canopy cover in occupied sites. The lack of consistency among studies indicates regional variability in the habitat structure of sites occupied by Northern Saw-whet Owls, but a dependable reliance on dense cover. Historic records show that Northern Saw­ whet Owls (Aegolius acadicus) occasionally breed in northern Indiana, and migrant popu­ lations spend the winter across the state (Cannings 1993). Christmas Bird Count records have also consistently (since 1985) documented the presence of Northern Saw-whet Owls wintering in south-central Indiana. Between fall and spring migration events, potential south-central Indiana forest sites were surveyed for Northern Saw-whet Owls to characterize occupied habitats in the winters of 2003/2004 and 2004/2005. Northern Saw-whet Owls undergo an annual fall movement from their primary breeding range in boreal forests along the U.S.-Canada border to points as far south as the Gulf Coast (Weir et al. 1980; Cannings 1993; Swengel & Swengel 1997). This partial migration has a high degree of variability due to irruptive years when the number of migrating Northern Saw-whet Owls can be ten times higher than the longterm average (Weir et al. 1980; Whalen & Watts 2002). Breeding Northern Saw-whet Owls are usu­ ally found in coniferous or mixed coniferous­ deciduous forests with a well-developed middle canopy of coniferous trees (Cannings 1993). Wintering and migrating Northern Saw-whet Owls appear to rely on dense vegetation for

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