A multi‐isotope (δ²H, δ¹³C, δ¹⁵N) approach to establishing migratory connectivity of Barn Swallow (Hirundo rustica)

Abstract

Establishing geographic links between different stages of the annual cycle of migratory species is fundamental to evaluating factors limiting their populations. Stable isotope measurements (δ13C, δ15N, and δ2H) of feathers combined with a knowledge of how these isotopes are structured spatially in foodwebs can be used to establish molt origins and migratory connectivity. Here, we investigated patterns of migratory connectivity between North American breeding grounds and South American wintering grounds of stable (n = 3) and declining (n = 9) populations of Barn Swallow (Hirundo rustica) in North America using a probabilistic assignment to multi‐isotope feather clusters derived for 488 winter‐grown feathers collected during the breeding season (2009 to 2012). Our study did not find evidence for differential degree of migratory connectivity between increasing/stable and declining populations of Barn Swallows but found a longitudinal structure in breeding and wintering ground origins of populations. Probable wintering areas for northern and western breeding birds corresponded with western regions of South America, while birds breeding in southern and eastern North America tended to occupy areas in north‐eastern South America. Possible factors contributing to the differential population trends between stable or increasing and declining breeding populations could be related to habitat quality of the different wintering areas, changes in climate, and the cost of long‐distance migration. The use of a multi‐isotope approach and the combination of prior information on geographic distribution of vegetation types, based on δ13C measurements, effectively constrained geographic origins of swallows and our approach can be applied to defining migratory connectivity for other species.

Topography of the Andes Mountains shapes the wintering distribution of a migratory bird

“…A similar longitudinal geographic gradient of origin has been inferred in several species of Nearctic-Neotropical migrants (Boulet et al, 2006;Norris et al, 2006;Garc ıa-P erez & Hobson, 2014;Rushing et al, 2014;Hobson et al, 2015), and it is often attributed to the legacy of Pleistocene glaciations when many species were confined to forested refuges in the southwest and the south-east of North America (Ruegg et al, 2006;Newton, 2008). A similar longitudinal geographic gradient of origin has been inferred in several species of Nearctic-Neotropical migrants (Boulet et al, 2006;Norris et al, 2006;Garc ıa-P erez & Hobson, 2014;Rushing et al, 2014;Hobson et al, 2015), and it is often attributed to the legacy of Pleistocene glaciations when many species were confined to forested refuges in the southwest and the south-east of North America (Ruegg et al, 2006;Newton, 2008).…”

Genetic assignment with isotopes and habitat suitability (gaiah), a migratory bird case study

“…carbon, nitrogen, sulphur) into a multivariate assignment framework could improve the accuracy of single isotope‐based assignments as has been demonstrated in numerous other taxa (Sellick et al . ; Hobson, Møller & Van Wilgenburg ; García‐Pérez & Hobson ; Veen et al . ).…”

Differences in spatial synchrony and interspecific concordance inform guild‐level population trends for aerial insectivorous birds

“…Our findings also emphasize the need for an improved understanding of migratory connectivity among aerial insectivores, and migratory birds in general (Hobson et al ). Though little is known about the connectivity of the species studied here, there are interesting clues that declining and stable or increasing populations of some species may winter in different locations or migrate at different times, suggesting a key role for overwintering conditions (Rohwer et al , García Pérez and Hobson , Hobson et al ). The lack of synchronicity among species and regions on the breeding grounds further suggests that non‐breeding conditions, e.g.…”