Abstract
Migrating species and populations are affected by conditions existing across large geographical scales. The degree to which populations mix at stop-over sites and wintering grounds is variable and can involve important fitness consequences. Thus, the link between breeding and wintering grounds and seasonal shifts in population structure are important to understand population demographics, local adaption and diversification patterns. This work aims to infer migration patterns and population connectivity in the Reed Bunting (Emberiza schoeniclus) community of a Ramsar-designated wetland, Lake Neusiedl, Seewinkel, Austria. Stable isotope markers (hydrogen, δ2H, carbon, δ13C) in feathers were analyzed to assign individuals to a specific breeding or natal area. Based on the geographic assignment, birds were compared with respect to their ecomorphological traits and their habitat selection (large reed bed versus more open habitat at shore of an alkaline lake) during winter to assess potential ecological differences and possibly associated morphological divergence. Stable isotope data revealed that the local Reed Bunting community undergoes seasonal changes in population structure. Three different populations that vary in their δ2H signature and to some extent in morphological characteristics as well as in δ13C values were identified. Indications for differential migration related to age and/or sex were additionally found, since males and females as well as first-year birds and adults showed remarkable differences in their traits and feather isotope values. δ2H values diverged significantly between these groups in both age and sex classes and birds with highest feather δ2H values were considered to represent the local breeding population at Lake Neusiedl and possibly also Reed Buntings from close surroundings. Moreover, this group had the highest δ13C values in first-year individuals as well as in adults. In both sex classes, the assignment of Reed Buntings to different populations was ultimately possible due to differences in bill shape with residents being characterized by more massive bills than individuals belonging to populations visiting the study area only during migration or for wintering. During winter, beak shape and feather δ2H and δ13C values differed significantly between birds caught in the reed stand of Lake Neusiedl and those captured near the salt pan, hence, indicating differential habitat selection among co-occurring populations during winter. These findings suggest that morphological attributes, such as bill shape and size as well as linked adaptations to different food sources play a decisive role for niche segregation among wintering populations. The results provide evidence that different populations mix during migration and during winter at Lake Neusiedl and the extent to which they are specialized to a specific habitat varied.
Highlights
In contrast to animals that spend their entire lives within a local home range, migrant species are affected by environmental conditions existing across larger geographical areas (Arizaga et al 2015)
We calculated a distance matrix based on the stable hydrogen and carbon isotope values, which led to three separate isotopic clusters
Birds from the first two clusters were present at Lake Neusiedl only in spring
Summary
In contrast to animals that spend their entire lives within a local home range, migrant species are affected by environmental conditions existing across larger geographical areas (Arizaga et al 2015). Migratory species differ in the degree to which individuals from distinct breeding localities mix on different stopover sites and wintering grounds (Chabot et al 2012; Marra et al 1998). The link between breeding, stopover and wintering sites can have important fitness consequences for migrating individuals. Patterns of connectivity between breeding and wintering grounds of migrating species are; highly significant for their evolution, ecology and conservation (Arizaga et al 2015; Webster and Marra 2005; Woodworth et al 2016). To understand population demographics, local adaptations and causes of diversification, the spatial characteristics (i.e. which populations mix on breeding and on wintering grounds) and the strength of migratory connectivity must be quantified (Chabot et al 2012; Webster et al 2002)
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