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Integrating genetic and stable isotope analyses to infer Snowfinch population’s connectivity

Integrating genetic and stable isotope analyses to infer the population structure of the White-winged Snowfinch Montifringilla nivalis in Western Europe. Resano-Mayor, J., Fernández-Martín, A., Hernández-Gomez, S., Toranzo, I., Espana, A., Gil, J.A., de Gabriel, M., Roa-Álvarez, I., Strinella, E., Hobson, K.A., Heckel, G. & Arlettaz, R. 2016. Journal of Ornithology. DOI: 10.1007/s10336-016-1413-8. VIEW

The population structure and seasonal movements of mountain birds in Europe are still largely unknown. This is partly because of the difficulties in studying them in such challenging environments (Chamberlain et al. 2012). Species living in high mountains now face acute risks of habitat loss, range contractions and local extinction due to current and projected climate change (Beniston 2003; Huntley et al. 2007; La Sorte & Jetz 2010). Therefore, a better understanding of the spatial structuring and movements among populations of European mountain birds is important from both the ecological and conservation points of view.

The White-winged Snowfinch Montifringilla nivalis is one of the most characteristic passerines of alpine habitats in Europe. Despite its breeding nuclei are relatively well-defined, we still know little about the specie’s population structure and wintering movements. Traditionally, the Snowfinch populations in Europe have been considered to be resident, with mostly local, seasonal elevational movements (del Hoyo et al. 2009). Yet, based on a 10 year ringing capture-mark-recapture programme conducted on a wintering population of the Spanish eastern Pyrenees, now we know that some individuals breeding in the European Alps move to the Pyrenees for overwintering. In particular, in 2006 we recovered one wintering individual in the eastern Pyrenees that had been ringed as a juvenile in the Austrian Alps (distance ca 1065 km) the previous breeding season. Moreover, three wintering individuals ringed in the eastern Pyrenees in 2009 were recovered in the Swiss and Italian Alps (distances of ca 501-760 km) between 2009 and 2012.

Despite the importance of bird ringing in deciphering the patterns of bird movements, ringing has the main limitation that recovery rates of individuals moving seasonally across large geographical areas are usually very low and can be affected by spatial heterogeneity. Alternative ways to elucidate patterns of bird migration have rapidly emerged in the past decades and, nowadays, the use of intrinsic markers, either genetic or isotopic, constitutes a promising and broadly used approach (Webster et al. 2002; Coiffait et al. 2009; Hobson 2011). Intrinsic markers are particularly useful because no prior capture of a given individual is required to infer migratory movements (Rubenstein & Hobson 2004; Hobson 2005). Overall, by combining the use of different intrinsic markers ecologists can now try to unravel patterns of bird movements, even if distances covered are vast and/or bird location remote (see Hobson & Wassenaar 2008).

Between 2009 and 2014, we sampled feathers from 48 Snowfinches during the breeding season (July and August) in the Cantabrian Mountains (CM), the Spanish central Pyrenees (CP) and the south-western Swiss Alps (SA). Moreover, samples from 56 wintering individuals (January to March) were also collected in the Spanish eastern Pyrenees (Fig. 1). By combining genetic and isotopic analyses our study examined past exchange among these breeding populations, and current winter movements of Alpine birds to the Pyrenees.

Resano-Mayor Fig 1Figure 1. Map of the study area. The monitored White-winged Snowfinch breeding populations included the Cantabrian Mountains (CM), the Spanish central Pyrenees (CP) and the south-western Swiss Alps (SA), which are the westernmost breeding grounds of the species’ European distribution. The monitored wintering population was in the Spanish eastern Pyrenees (EP)

Population genetic structure
The most common haplotypes, except one, were widespread among breeding populations. We found, however, one haplotype being specific and predominant in the CM. When considering the wintering individuals in the EP, most of them had the same common widespread haplotypes found in the breeding populations but none showed the specific haplotype from the CM (Fig 2). Therefore, while our results suggest an absence of clear genetic structure in the populations investigated, the population in the CM seems to be more isolated as indicated by its specific and predominant haplotype. In this regard, identifying populations with a special genetic composition is important because they may serve as a long-term store of species’ genetic diversity, and should therefore be of specific conservation concern. The genetic data alone, however, are not informative of whether movements between populations still occur because the patterns we observe currently reflect past exchanges among breeding populations.

Resano-Mayor Fig 2Figure 2. Haplotype network based on mitochondrial DNA from the White-winged Snowfinch (subspecies nivalis). Each circle represents a different haplotype (n = 11). Different colours refer to individuals sampled in the Cantabrian Mountains (black), the Spanish central Pyrenees (dark grey) or the Swiss Alps (grey) during the breeding season, and the Spanish eastern Pyrenees (light grey) during the wintering season (see legend). Circle size represents the relative frequency of given haplotypes (the number of individuals exhibiting the corresponding haplotype is also provided). Haplotypes are connected by straight lines and each breaking node indicates a single step mutation

Wintering movements
No differences in hydrogen stable isotopes from primary feathers were found among breeding populations. Thus, by analysing the primaries, we could not assign wintering individuals in the EP to particular breeding grounds. Nevertheless, the rectrices from some wintering birds in the EP showed considerably lower isotopic values compared to those from breeding birds at the CM or the CP, which could correspond to breeding birds from the Alps where post-breeding moulting grounds are at considerably higher altitudes. If this pattern is confirmed in the future, we could assign the proportion of wintering Snowfinches at the Pyrenees with Alpine breeding origins. This would support the hypothesis that Snowfinches during the winter can be more mobile than previously thought, as supported by the few ring recoveries showing breeding birds from the Alps wintering in the Pyrenees.

Resano-Mayor Fig 3Figure 3. White-winged Snowfinch wintering group in the Spanish eastern Pyrenees © Ignasi Tornado

Overall, understanding White-winged Snowfinch population structure and seasonal movements represents an essential step forward. This is because the species’ potential to adapt to climate change will partly depend on its elevational movements and its capacity to move among mountain ranges in order to find the most suitable conditions for breeding and overwintering. Further studies combining ringing and the analyses of intrinsic markers (e.g. microsatellites for a deeper understanding of the genetic structure or hydrogen stable isotopes for deciphering the magnitude of birds moving between breeding grounds in the Alps and wintering sites in the Pyrenees) are essential for a better understanding of the population structure and dynamics of the White-winged Snowfinch in western Europe. That would represent an essential step for better appraising the species’ metapopulation dynamics and guiding conservation efforts.

References and further reading

Benison, M. 2003. Climatic change in mountain regions: a review of possible impacts. In: Climate Variability and Change in High Elevation Regions: Past, Present & Future: 5-31. Springer Netherland. VIEW

Chamberlain, D., Arlettaz, R., Caprio, E., Maggini, R., Padroni, P., Rolando, A. & Zbinden, N. 2012. The altitudinal frontier in avian climate impact research. Ibis 154:205–209 VIEW

Coif fait, L., Redfern, CP., Bevan, R.M., Newton, J. & Wolff, K. 2009. The use of intrinsic markers to study bird migration. Ringing & Migration 24:169–174 VIEW

del Hoyo, J., Elliott, A. & Christie, D.A. 2009. Handbook of the Birds of the World. Vol. 14. Bush-shrikes to Old World Sparrows. Lynx Edicions, Barcelona.

Hobson, K.A. 2005. Using stable isotopes to trace long-distance dispersal in birds and other taxa. Divers Distrib 11:157-164. VIEW

Hobson, K.A. 2011. Isotopic ornithology: a perspective. J Ornithol 152:49-66. VIEW

Hobson, K.A. & Wassenaar, L.I. 2008. Tracking Animal Migration using Stable Isotopes (Vol. 2): p.188. Handbook of Terrestrial Ecology Series, Academic Press / Elsevier, Amsterdam.

Huntley, B., Green, R.E., Collingham, Y.C. & Willis, S.G. 2007. A climatic atlas of European breeding birds. The RSPB and Lynx Edicions, Barcelona.

La Sorte, F.A. & Jetz, W. 2010. Projected range contractions of montane biodiversity under global warming. Proc R Soc Lond B Biol Sci 277:3401-3410. VIEW

Rubinstein, D.R. & Hobson, K.A. 2004. From birds to butterflies: animal movement patterns and stable isotopes. Trends Ecol Evol 19:256-263. VIEW

Webster, M.S., Marra, P.P., Haig, S.M., Bensch, S. & Holmes, R.T. 2002. Links between worlds: unraveling migratory connectivity. Trends Ecol Evol 17:76-83. VIEW


Image credit

Featured image: adult White-winged Snowfinch Montifringilla nivalis feeding a fledgling in the Swiss Alps © Nathan Horrenberger

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