Popular Science: Feathers can tell the origin
In recent studies, researchers have focused on the origin of individual geese that winter in the Camargue Nature Park in the Rhône delta of southern France. They also examined whether they come from the Czech Republic, where they currently breed and molt. Birds that do not breed in a certain year, especially young birds (the goose begins reproduction in the second or third year of its life) and the male, fly to the molting area. Authors have collected feather samples from 147 individuals during the 2008–2009 and 2017–2018 hunting seasons, which they later analyzed using stable H isotopes (δ2H) to determine the origin of the birds. The δ2H values in feathers and precipitation in the area where the individuals grew up correlated well. Therefore, the values of stable isotopes of hydrogen were determined on the basis of the rainwater of the growing season, further calibrated using the calibration equation for European Mallards based on the keratin standard δ2H values, since the equation for the greylag goose has not yet been determined.
Stable hydrogen isotope analyses of the feathers showed that their values in the analyzed feathers were consistent, with their geographical origin across Europe in the same latitude extending from Great Britain across north-central Europe, particularly consistent with Poland and north-eastern Germany. However, geese in the UK either winter on the British Isles or are “feral”, breeding and wintering in the UK. Therefore, the researchers concluded that the geese came mainly from north-central Europe, as the core identified in Poland and north-eastern Germany. Nevertheless, the Czech Republic was not excluded as a region of origin, only there was a lower probability of occurrence. As with any model, the results carry a certain percentage of uncertainty. However, unlike carbon or nitrogen isotopes, isotopes of hydrogen seem to be the most accurate, as there is little spatial variation in carbon isotopes in Europe and there are considerable issues as to the determination of nitrogen in relation to anthropogenic inputs.
Even so, the results were surprising because most ring recoveries and observations of neck collars rather suggest a Czech origin. However, it is perhaps due to the reason that rings are often fitted on birds on the hatching area and the breeding grounds, while the isotopes are related to where the feathers were grown or molted. It is possible that wintering birds in the south of France, who bred in Czech Republic in recent years, molted in Poland and north-eastern Germany.
The final results of the origin of greylags wintering in the south of France, with a combination of stable isotopes and ringing data, point to central Europe, specifically the Czech Republic, Poland and north-eastern Germany. This refutes the origin of the greylag geese in the Nordic countries (Norway, Sweden), which generally winter in north-eastern France and the Atlantic coast. This information is key to overall management, such as changes in hunting legislation and regulations, and it is necessary to consider that in the new international management plan for the NW/SW European population, which mostly considers the birds breeding in Fennoscandia (Scandinavia, Finland, Karelia, Kola Peninsula) and Western Europe.
Guillemain, M., Bacon, L., Kardynal, K.J., Olivier, A., Podhrazsky, M., Musil, P., Hobson, K.A. (2019): Geographic origin of migratory birds based on stable isotope analysis: the case of the greylag goose (Anser anser) wintering in Camargue, southern France. European Journal of Wildlife Research, 65: 67. https://doi.org/10.1007/s10344-019-1304-4.