Friday, October 12, 2012: 8:00 PM
6C/6E (WSCC)
Stable carbon and nitrogen isotope analysis can be useful for examining avian dietary patterns and food web dynamics. Stable carbon isotopes can provide information on sources of organic matter while stable nitrogen isotopes may provide a more accurate way of quantifying trophic status compared to traditional field surveys and information from the natural history literature. A field and stable isotopic study was conducted to compare the diet of migratory songbirds with that of resident birds. Birds were captured using mist nets at sites located in Texas (Gulf Coast Bird Observatory, Lake Jackson, TX) between October and November 2011 and Costa Rica (La Selva Biological Station, Puerto Viejo, Heredia) during February 2012. The first and second primary feathers were removed from each wing. Feathers were cleaned using 70% isopropyl alcohol and air dried for ~15 min. Feathers were then analyzed for δ13C and δ15N using the elemental analyzer isotope ratio mass spectrometer (EA IRMS). Life history information indicates that both migrant and resident bird’s main feeding guild is insectivorous; however the isotopic results indicate significant differences in trophic positions (δ15N; P= <0.0001) and carbon sources (δ13C; P = 0.0002) between migrant and resident birds. Mean (± SD) δ15N values for migrants was 5.6±1.2‰ and δ13C was ‑23.9±0.9‰ (n = 12). Mean (± SD) δ15N values for residents was 8.1±0.8‰ and δ13C was -18.4±3.5‰ (n = 12). These preliminary results suggest different food sources for migrant and resident birds. In particular, a higher δ15N value for residents indicates a higher trophic status.