Natal origin of black ducks harvested during the sport hunt in Québec, Canada

In Québec, Canada, the American black duck (Anas rubripes) breeds mainly in the boreal forest to the north, but a small segment of the population breeds in southern Québec in the densely populated agricultural areas surrounding the St. Lawrence River and Estuary. This agricultural breeding population faces increasing pressure from urbanization, competition with mallards (A. platyrhynchos), landuse changes, and hunting. In Québec, approximately 69% of black ducks are harvested in agricultural landscapes. Most birds harvested in Québec are taken in September, during the first 3 weeks of the hunting season, when birds breeding in the boreal habitat are unlikely to have initiated their southbound fall migration. This additional pressure on the agricultural breeding population could be detrimental to its long-term sustainability. We measured carbon (δ¹³C), nitrogen (δ¹⁵N), hydrogen (δD), and sulfur (δ³⁴S) isotopie compositions of feathers from hatching-year black ducks of known natal origin (banded birds) and used these to develop a multivariate logistic regression classification model based on habitat type. We then applied this model to feathers from birds harvested in Québec during the fall sport hunt in those same years to determine their natal origin. Sixty percent in 2004 and 17% in 2005 of black ducks harvested during the fall sport hunt in Québec originated from the agricultural segment of the population, compared to 36% and 72% in those same years originating from the boreal area. This is in stark contrast to the species' distribution in Québec, with only approximately 4% of the population breeding in the agricultural portion of the province. Our results suggest that this harvest bias toward the agricultural segment of the breeding population, which may be accentuated in years when migration is delayed, could compromise its long-term sustainability. We highlight the importance of existing regional survey programs, and the information gaps that exist concerning the natal origin of black ducks harvested in the northeastern United States, and the annual productivity of the agricultural black duck population in Québec. Stable isotopes from samples of known natal origin (banded birds) proved an effective tool to identify the natal origin of hunted birds. However, we caution against the use of published isotopie thresholds (δ¹³C, δ¹⁵N) to infer the origin of migrating organisms in small study areas.