n Appraisal of the use of Hydrogen-Isotope Methods to Delineate Origins of Migratory Saw-Whet Owls in North America

• Northern Saw-whet Owls (Aegolius acadicus) breed throughout the boreal forest of North America, but little is known about their population trends or distribution within this region. Analysis of stable hydrogen isotopes (delta H-2) in feathers can delineate origins of a variety of avian migrants, but raptors are reported to have high infra-feather isotopic variance and mean delta H-2 values higher than predicted from delta H-2 isoscapes specific to raptor feathers, making assignment of geographic origin sometimes difficult. We examined the applicability of delta H-2 analysis of saw-whet owl feathers to delineating origins of migrants and to assessing differences in the migratory behavior of adult and young owls by using multiple generations of feathers from owls captured during fall migration at the Delta Marsh Bird Observatory, Manitoba, 2006-2007. Values of delta H-2 in saw-whet owl feathers were higher than predicted from a delta H-2 isoscape specific to raptor feathers and from patterns of movements inferred from analysis of band recoveries. This effect was pronounced in adults, while values of delta H-2 in feathers of hatching-year owls fell primarily within the range predicted for the boreal forest northwest of Delta Marsh. Significant differences in delta H-2 values among feather generations suggest that physiological or behavioral differences between adults and young give rise to greater H-2 enrichment in adult feathers. These results indicate that current delta H-2 isoscapes for feathers cannot be used to track adult saw-whet owls reliably and further research into the mechanisms of H-2 enrichment in owl feathers is required.

Ämnesord

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

Nyckelord

deuterium

isotope

Manitoba

migration

Saw-whet Owl

stable

Aegolius acadicus

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