STABLE ISOTOPES AND SOLVING MIGRATORY MYSTERIES OF BIRDS OF PREY

Most research on threatened or endangered bird species takes place on their breeding grounds. During the breeding season, birds are relatively easier to locate and study. Knowledge of what happens to migratory birds after the breeding season is relatively limited. To know migratory routes and over-wintering locations allows for year-round conservation. In addition, accurate population modeling requires the separation of inter-year mortality from permanent emigration. Telemetry and mark and recapture techniques are traditional methods of monitoring the inter-year movements of birds. The usefulness of radio- or satellite-tracking is limited by sample sizes, logistics and expense. Mark-recapture methods such as bird banding are relatively less expensive, but the rarity of the recapture of migratory birds also limits sample sizes. Band recovery studies also likely miss important long-distance dispersal events. Stable isotope analysis (SIA) of feathers provides a method for tracking migrations, the determination of wintering grounds and the estimation of inter-year dispersal patterns at scales greater than single populations or study areas. With the application of SIA, we determined that a banding station on the Gulf Coast of Texas could be used to remotely monitor the populations of Peregrine Falcons (Falco peregrinus) breeding in western Arctic. We also determined that Burrowing Owls (Athene cunicularia hypugaea) breeding in Canada spend their winters in southern Texas to Central Mexico. Finally, we demonstrated that Burrowing Owls have a low degree of breeding-site fidelity and disperse between breeding season at larger scales than previously suspected. The latter discovery will lead to a readjustment of current over-winter mortality rates and more accurate population models for the conservation of Burrowing Owls.