Forage site selection, latitudinal migration and altitudinal migration studies in birds

I seek to understand the foraging ecology and migration ecology of birds wintering in temperate and tropical climates. For foraging ecology study, I used a stuffed peregrine falcon (Falco peregrinus) to directly test the hypotheses that the presence of a predator will (1) cause birds to select higher foraging sites than they would in the absence of a predator, and (2) affect the distance from cover at which birds forage. Our results showed that both the presence of the falcon and its location influenced the foraging locations chosen of passerines along the horizontal axis, but not vertical axis. For migration study, I am interested in the application of stable isotope approaches to the study of latitudinal and altitudinal migration of birds in Asia. For the latitudinal migration study, I found that the analyses of multiple stable isotopes (delta13C, delta15N, delta 18O and deltaD) can provide an understanding of the number of breeding populations represented at large congregations of wintering birds, probable locations of these breeding populations, and which breeding populations do not contribute migrants to a wintering site in Asia. To determine whether stable isotopes can be potentially used for the inference of the breeding origins of montane birds migrating between altitudes, I examined feather delta 15N and delta13C values from 27 wild passerines collected along an altitudinal gradient of Taroko National Park in Taiwan. I found feather delta 15N values decreased and delta13C increased with increasing altitudes systematically for herbivores, omnivores and insectivores, although the patterns exhibited some differences between the three feeding guilds. The findings of altitudinal trends in feather delta15N and delta13C values suggest that these two isotopes may serve as population markers and indicators of breeding origins for future studies of altitudinal migration of passerines, whether they are herbivorous, omnivorous or insectivorous.