ORIGINAL ARTICLE Unraveling migratory connectivity of two European diving ducks: a stable isotope approach Alain Caizergues 1 & Steven L. Van Wilgenburg 2 & Keith A. Hobson 3,4 Received: 11 March 2016 /Revised: 7 September 2016 /Accepted: 13 September 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract Quantifying the strength of migratory connectivity or the degree to which breeding and wintering populations are connected is crucial for conservation and management of mi- gratory birds. Using stable hydrogen isotope ratios of second- ary flight feathers (δ 2 H f ), we assessed the breeding origins/ locations of 666 common pochards (Aythya ferina) and 190 tufted ducks (A. fuligula) captured in France during the 2005– 2006 and 2008–2009 wintering seasons. Isotopic values of common pochards wintering on Grand-lieu Lake (western France) displayed a marked bimodal spatial distribution sup- portive of strong contributions of both northern (60–65° of latitude) and central European (45–55° of latitude) origins. According to the temporal distribution of δ 2 H f values, the presence of common pochards of northern origin reached a maximum at the peak of the wintering season (December– January). In contrast, tufted duck did not display a clear bi- modal pattern in δ 2 H f , with individuals displaying a more northerly origin (60–70° of latitude), likely of Russian and Scandinavian origin. First-year individuals had more northern origins than adults, suggesting that either isotopic discrimina- tion differed among age groups or, more probably, that some adults may undergo moult at latitudes lower than that of their breeding ground. Tufted ducks with northerly δ 2 H f values were observed early in the season in individuals sampled in eastern France and late in the season in those sampled in western France. The effects of winter severity on the distribu- tion of individuals over the wintering range were supported for the tufted duck with more northerly values recorded during harsh winters. Management implications of these results are discussed. Keywords Breeding origin . Common pochard . Deuterium . Migratory connectivity . Natal origin . Stable isotopes . Tufted duck Introduction Understanding patterns of recruitment into harvested popula- tions is crucial to effectively manage game populations and requires estimating parameters such as reproductive success, survival, immigration, and emigration. Although estimating survival and reproductive success is feasible through the use of standard capture-mark-recapture (CMR) approaches (e.g., Lebreton et al. 1992), investigating individual movements or identifying areas of greatest productivity or recruitment into harvested populations is usually not straightforward. Such in- formation is required because even subtle differences in movements can profoundly affect estimates of population tra- jectories (see Hawkes 2009). In many migratory waterfowl, individuals leave their breeding range to gather in large numbers at staging areas and other locations during the wintering season (Newton 2008). In such species, establishing the link between breeding and non-breeding areas (i.e., migratory connectivity) is crucial for effective management because it allows the delineation of * Alain Caizergues alain.caizergues@oncfs.gouv.fr 1 Office National de la Chasse et de la Faune Sauvage, Migratory Birds Unit, 8, avenue Albert Einstein, Bât B, CS 32355, 34323 Nantes Cedex 3, France 2 Environment and Climate Change Canada, 115 Perimeter Road, Saskatoon, Saskatchewan S7N 0X4, Canada 3 Environment and Climate Change Canada, 11 Innovation Blvd., Saskatoon, Saskatchewan S7N 3H5, Canada 4 Department of Biology, University of Western Ontario, London, Ontario, Canada Eur J Wildl Res DOI 10.1007/s10344-016-1048-3