Age-related differences in the fall migration of Northern Saw-whet Owls
Age-related differences in the fall migration of Northern Saw-whet Owls.
EMILY A. CARUANA, SARAH M. MUSILLI, MICHAEL S. HURBAN, Dept. Biol. & Physics, Canisius Coll., Buffalo, NY; SCOTT WEIDENSAUL, Ned Smith Center for Nature and Art, Millersburg, PA; H. DAVID SHEETS and SARA R. MORRIS, Dept. Biol. & Physics, Canisius Coll.
Age-related differences in the fall migration of Northern Saw-whet Owls in Pennsylvania were investigated during 1998 - 2003. Overall, 55.5% (n = 2369) of owls captured during mist netting were HY. During the six years of the study, the average date of arrival was significantly earlier for young owls than adult owls at these sites. Similar analyses of the annual timing of migration revealed significant differences in 1998, 1999, and 2001, but no significant difference in timing of migration for 2000, 2002, and 2003. Adult owls had significantly higher mass and longer wing chords, but also had lower keel score (indicating a lower condition) than young owls. Analyses of fat scores and condition indices did not reveal any significant differences between the age groups. A significantly higher percentage of adult owls was recaptured than young owls. Additionally, minimum stopover was longer for adult owls at 5.6 d than for young owls at 3.5 d. Both adult and young owls lost mass between captures, although this was only significant among adult owls, and the difference between the age groups was not significant. Our results indicate that there are substantial differences in some aspects of migration and stopover ecology between age groups, but reasons for these differences are unclear.