Stable isotopes as indicators of altitudinal distributions and movements in an Ecuadorean hummingbird community

Abstract

Altitudinal migration and dispersal is an important component of the life history of several temperate and tropical birds but remains poorly understood due to the limited success of mark and recapture techniques. Stable isotopes of hydrogen (δD) in rainfall, and to a lesser extent, carbon (δ13C) in plants are known to change with altitude and hence may provide the basis of a technique for tracking the altitudinal movements in birds and other wildlife. We investigated the potential for this technique by measuring δ13C, δD, and δ15N values in tail feathers of eight species of hummingbirds (Phaethornis malaris, P. syrmatophorus, P. guy, Adelomyia melanogenys, Coeligena torquata, C. lutetiae, Metallura baroni, M. williami) along an altitudinal gradient (300-3,290 m asl) in the Andes Mountains of Ecuador. Feather δ13C and δD values were correlated and each changed significantly with elevation above 400 m. In general, we found good agreement between feather δD values and those predicted from a generalized relationship of precipitation and surface water δD with altitude. Similarly, feather δ13C values showed an enrichment of ∼1.5‰ per 1,000 m over the linear portion of the elevational response. Stable-nitrogen isotope values were variable, and so did not provide useful information on elevation in birds, apart from trophic effects. Overall there appears to be good potential for using the (δD, δ13C) stable isotope approach to track altitudinal movements and to elucidate previously unrecognized patterns of life history variation in both temperate and tropical species that migrate across elevational isotopic gradients.