Abstract
Accumulations of shed caribou antlers (Rangifer tarandus) are valuable resources for expanding the temporal scope with which we evaluate seasonal landscape use of herds. Female caribou shed their antlers within days of giving birth, thus marking calving ground locations. Antler geochemistry (87Sr/86Sr) reflects the isotopic signature of regions used during antler growth, thereby providing data on a second component of seasonal landscape use. Here, we evaluate shed caribou antlers from the Coastal Plain of the Arctic National Wildlife Refuge, Alaska. The Central and Eastern regions of the Coastal Plain are calving grounds for the Porcupine Caribou Herd, while the Western Coastal Plain supports calving by the Central Arctic Herd. We found that antler 87Sr/86Sr from the Central and Eastern Coastal Plain were isotopically indistinguishable, while antler 87Sr/86Sr from the Western Coastal Plain was significantly smaller. For each region, we compared isotopic data for “recent” antlers, which overlap the bulk of standardized state and federal caribou monitoring (early 1980s and younger), with “historical” antlers shed in years predating these records (from the 1300s to the 1970s). For Porcupine Herd females calving in the Arctic Refuge, comparisons of antler 87Sr/86Sr through time indicate that summer ranges have been consistent since at least the 1960s. However, changes between historical and recent antler 87Sr/86Sr for the Central Arctic Herd indicate a shift in summer landscape use after the late 1970s. The timing of this shift is coincident with multiple factors including increased infrastructural development in their range related to hydrocarbon extraction. Accumulations of shed caribou antlers and their isotope geochemistry extend modern datasets by decades to centuries and provide valuable baseline data for evaluating potential anthropogenic and other influences on caribou migration and landscape use.
Highlights
Seasonal landscape use is a core component of animal ecology and population biology and is influenced by a variety of factors including population size, climate, and anthropogenic impacts (Fryxell and Sinclair, 1988; Dingle, 2006; Avgar et al, 2014)
The Coastal Plain of the Arctic Refuge is a broad, flat, tussock-tundra-rich landscape used as a caribou calving ground by the Porcupine Herd and the Central Arctic Herd (Figure 1; Cameron et al, 2002; Griffith et al, 2002; Jorgenson et al, 2002; Jorgenson and Walker, 2018)
The summer ranges of both herds overlay unconsolidated Quaternary sediments, but the range of the Porcupine Herd extends east and south into regions dominated by metasediments, mafic rocks, and Neoproterozoic siliciclastic rocks (Wilson et al, 2015; Colpron et al, 2016), while the range of the Central Arctic Herd extends west into areas richer in Mesozoic carbonates as well as Mesozoic and Cenozoic siliciclastic rocks (Wilson et al, 2015)
Summary
Seasonal landscape use is a core component of animal ecology and population biology and is influenced by a variety of factors including population size, climate, and anthropogenic impacts (Fryxell and Sinclair, 1988; Dingle, 2006; Avgar et al, 2014). While historical ecology remains mostly lost to time, an increasing number of ecological proxies can help quantify the magnitude and directions of otherwise cryptic biological changes, including aspects of landscape use and migration (Morneau and Payette, 1998, 2000; Zalatan et al, 2006; Kidwell, 2007; Froyd and Willis, 2008; Behrensmeyer and Miller, 2012; Kidwell and Tomasovych, 2013; Miller et al, 2013; Dietl et al, 2015; Barnosky et al, 2017; Grace et al, 2019) Bones are one such proxy, as they can persist on landscape surfaces for decades, centuries, or longer and can faithfully record data on their source populations (Behrensmeyer, 1978; Andrews, 1995; Sutcliffe and Blake, 2000; Western and Behrensmeyer, 2009; Miller, 2011; Behrensmeyer and Miller, 2012; Miller et al, 2013). After decades, shed antlers can accumulate into measurable densities on landscape surfaces (e.g., 102-103 antlers/km2), with regions of relatively high or low antler densities faithfully recording the herd’s patterns of seasonal landscape use (Miller and Barry, 1992; Miller, 2012; Miller et al, 2013)
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