The Use of Hydrogen Stable Isotopes in Claws to Distinguish Between Migratory and Resident American Kestrels (Falco sparverius)

Partial migrant populations have individuals that migrate while others remain resident. American Kestrels ( Falco sparverius ) in southern Idaho are partial migrants. Individuals may migrate away from S. Idaho in winter, remain resident, or migrate south to winter in Idaho. Ratios of Hydrogen (H) and Deuterium (D) vary along a latitudinal gradient with values ranging from -140‰ near northern poles and 0‰ at the equator. We evaluated whether stable isotope ratios of H/D from keratin in claw tissue (δD _c ), which reflect the diet 3-4 months previous, could be used to distinguish between migratory and resident kestrels. We collected small claw samples in breeding and wintering seasons over three years. Claw samples were washed, weighed, pyrolyzed through gas chromatography and analyzed by a mass spectrometer. Preliminary results indicate that δD _c of adult birds in spring are isotopically enriched compared to adults in winter. However, δD _c of adult breeding birds is higher compared to nestling δD _c, indicating a shift associated with age. This result is similar to shown δD in kestrel feathers. Results suggest that δD _c of American Kestrels may be useful to identify migratory strategies.