An isotope (δ34S) filter and geolocator results constrain a dual feather isoscape (δ2H, δ13C) to identify the wintering grounds of North American Barn Swallows

Abstract

ABSTRACT The discovery of spatial patterns in naturally occurring isotopes (e.g., δ2H, δ13C) at continental scales has been tremendously important in providing a method to infer potential breeding and wintering origins of migratory animals through assignment to tissue-specific isoscapes. Single-isotope (i.e. δ2H) assignments of birds to molting origins in South America have been limited by the lack of strong spatial gradients in precipitation δ2H there. We integrated an mvnpdf (multivariate normal probability density function) approach using δ2H and δ13C values in tail feathers to determine wintering origins of adult Barn Swallows (Hirundo rustica) breeding in eastern Canada (n = 208). Spatial assignments were conducted using precipitation (δ2H) and theoretical plant-based (δ13C) isoscapes for South America calibrated for feathers of Nearctic–Neotropical migrant songbirds. We also measured feather δ34S values of Barn Swallows equipped with geolocators (n = 9) and of a larger group of Barn Swallows (n = 12...