Lack of Stable-Isotope Differences Between Canada Goose Populations Nesting in the Subarctic and Temperate Zones

Ratios of stable isotopes in feathers have great potential for identifying the connectivity of bird migrations and the origin of harvested individuals of game species. In particular, the relationship between the hydrogen ratio due to latitudinal variation in precipitation (δDp) and that in feathers (δDf) is often used to determine unknown individuals’ latitude of origin. We assessed this relationship between Canada Geese nesting in the temperate zone (Branta canadensis maxima) and the subarctic (B. c. interior). For this game species, the origin of harvested birds is important for developing management that maintains a desirable level of harvest while ensuring continued viability of all subspecies and breeding populations. We collected freshly grown primaries from three populations of interior and five of maxima and analyzed them for δD, δ13C, and δ15N. Multivariate analysis suggested no overall differences in isotopic composition between subspecies. A univariate assessment indicated a significant difference in δNf, despite substantial overlap between subspecies, and no difference in δDf or δ Cf. Of particular interest is the lack of difference in δDf, despite the large latitudinal differences in δDp and between the subspecies’ breeding ranges. Values of δDf averaged –131.85‰ ± 1.36 for interior, –131.63‰ ± 0.71 for maxima, and we found no overall relationship between δDf and δDp. Overall, our results suggest that δD, δ 13C, and δ15N alone have limited ability to discriminate between subspecies interior and maxima and hence have limited applicability for estimating the origin of harvested birds and/or identifying molt migrants of maxima.