Origins of harvested American black ducks: stable isotopes support the flyover hypothesis

Abstract

Waterfowl management is more effective when based on detailed information on population connectivity between breeding, wintering, and stopover sites. For the American black duck (Anas rubripes), a species of conservation concern, estimates for the fall age ratio at harvest differed depending on whether harvest data were derived from Canada or the United States, suggesting regional differences. Within Canada, hunters in Atlantic Canada were more likely to harvest black ducks from nearby breeding locations compared to hunters in southern Ontario and Quebec, Canada, who were more likely to harvest individuals from the Boreal Softwood and Taiga Shield of eastern Canada. Black ducks harvested in the United States are thought to originate predominantly from northern portions of the breeding range, leading to the flyover hypothesis, which postulates that black ducks produced in the Boreal Softwood and Taiga Shield region are less susceptible to harvest by hunters in Atlantic Canada and northeastern United States. To test the flyover hypothesis, we examined regional and temporal differences in the origins of harvested black ducks using feathers from wings (n = 664) submitted by hunters to the species composition and parts collection surveys across 3 hunting seasons (2017-2018, 2018-2019, 2019-2020). We used a likelihood-based assignment method that relied on feather stable-hydrogen isotopes (δ 2 H) and stable-carbon isotopes (δ 13 C) to determine the natal or molt origin of individuals harvested within eastern Canada and the United States. We also used a spatial clustering

Species Abundance Modelling of Arctic-Boreal Zone Ducks Informed by Satellite Remote Sensing

“…We also wanted to control for the variation in ABZ duck population size potentially driven by factors occurring outside the region. Specifically, in dry years in the PPR, ducks are believed to overfly the PPR and settle in the boreal forest [15,16], inflating boreal population sizes independent of boreal habitat conditions. To do this, our SAMs included annual pond count data (i.e., basins which were observed to have water) collected from the US and Canadian prairies during WBPHS surveys (Table 2).…”

“…Wetlands in the ABZ support millions of breeding and molting ducks [13,14] and act as refuge for drought-displaced ducks when conditions are dry in the Prairie Pothole Region [15,16]. Accurately identifying factors influencing spatiotemporal variation in abundance and distribution of ducks across vast landscapes with limited data like the ABZ is a challenging task [17] yet is critical to conservation and is particularly critical in regions such as the ABZ where waterfowl are central components of Indigenous people's livelihoods [18].…”

Assigning harvested waterfowl to geographic origin using feather δ2H isoscapes: What is the best analytical approach?

“…Another valuable, but uncommon, source is banded known-origin HY birds submitted to the North American Waterfowl Parts Collection [87] and Species Composition Surveys [62], although using these incidental sources of feather collection comes with some necessary assumptions (e.g., harvested individuals have not opportunistically regrown feathers since banding). These surveys are excellent sources of feathers from harvested birds [9,10,15] but have been underutilized to date. All δ 2 H f data used here are available [88] for future calibration studies and help build upon the literature describing these relationships (see S1 Table ).…”

“…This use of spatially explicit assignments to determine the origin of unmarked, migrant individuals using measurements of tissue stable-hydrogen isotopes (δ 2 H) has grown considerably over the past two decades (reviewed in [4]). In addition to numerous non-game animals, this isotopic approach has been applied to determine the geographic origins of several hunted waterfowl species across North America [5][6][7][8][9][10] and Eurasia [11][12][13][14]. In this context using the stable isotope approach, origin is generally not a specific location, but instead describes a probabilistically defined region that likely contains the location where an individual previously grew the sampled tissue(s) such as a natal, breeding, or non-breeding site.…”

“…In this context using the stable isotope approach, origin is generally not a specific location, but instead describes a probabilistically defined region that likely contains the location where an individual previously grew the sampled tissue(s) such as a natal, breeding, or non-breeding site. This assignment method has been important in improving our understanding of migratory connectivity, especially between breeding and harvest areas [8][9][10]15,16], and has the potential to contribute considerably to waterfowl management.…”