Pronounced Fidelity and Selection for Average Conditions of Calving Area Suggestive of Spatial Memory in a Highly Migratory Ungulate

Abstract

A distinguishing characteristic of many migratory animals is their annual return to distinct calving (birthing) areas in the spring, yet the navigational mechanisms employed during migration that result in this pattern are poorly understood. Effective conservation of these species requires reliable delineation of such areas, quantifying the factors that influence their selection, and understanding the underlying mechanisms resulting in use of calving areas. We used barren-ground caribou (Rangifer tarandus granti) as a study species and identified calving sites of the Western Arctic Herd in Alaska using GPS collar data from 2010–2017. We assessed variability in calving areas by comparing spatial delineations across all combinations of years. To understand calving area selection at a landscape scale, we performed a resource selection analysis comparing calving sites to available locations across the herd’s range and incorporated time-varying, remotely sensed metrics of vegetation quality and quantity. We found that whereas calving areas varied from year to year, this annual variation was centered on an area of recurring attraction consistent with previous studies covering the last six decades. Calving sites were characterized by high-quality forage at the average time of calving, but not peak calving that year, and by a narrow range of distinct physiographic factors. Each year, calving sites were located on areas of above-average conditions based on our predictive model. Our findings indicate that the pattern of spring migration for pregnant females was to migrate to areas that consistently provide high-quality forage when averaged across years, and then upon arriving at this calving ground, refine selection using their perception of annually varying conditions that are driven by environmental stochasticity. We suggest that the well-documented and widespread pattern of fidelity to calving grounds by caribou is supportive of a navigational mechanism based on spatial memory at a broad scale to optimize foraging and energy acquisition at a critical life-history stage. The extent to which migrants depend on memory to reach their spring destinations has implications for the adaptability of populations to changing climate and human impacts.

Seasonal patterns of spatial fidelity and temporal consistency in the distribution and movements of a migratory ungulate

“…High fidelity to calving grounds is the distinguishing and defining feature of caribou herds (Skoog, 1968), and WAH caribou have shown fidelity to their core calving grounds for at least 100 years (Cameron et al., 2020; Lent, 1966). WAH caribou showed highly significant fidelity to their core calving grounds at the regional scale, and this fidelity has been linked to areas with predictable high‐quality vegetation (Cameron et al., 2020).…”

Simulation modeling accounts for uncertainty while quantifying ecological effects of development alternatives

“…Study area map for the Development Impacts Analysis model within the National Petroleum Reserve—Alaska (NPR‐A). Approximate calving areas for the Teshekpuk Caribou Herd (TCH) and Western Arctic Herd (WAH) are depicted based on 75% kernel utilization distributions (Person et al 2007, Cameron et al 2020). Existing roads are sparse within the NPR‐A and include both those already completed (CD5, Greater Mooses Tooth 1 [GMT1]) and those under construction (GMT2).…”

“…The IAP DEIS also used this layer as part of its impact assessment (BLM 2019 a ). For the WAH, we used a relative calving habitat suitability raster, based on a similar resource selection approach as with the TCH (Cameron et al 2020). We resampled the WAH data from its original 30‐m resolution to match the 120‐m resolution of the TCH data (Fig.…”

“…We used 95% contour kernel density estimates of WAH calving areas from 2010 to 2017 (Fig. 3e; Cameron et al 2020), derived from GPS‐detected calving locations (Cameron et al 2018), to further refine the WAH calving suitability raster. Western Arctic Herd calving overlap values, ranging from 0 to 8 yr, were intersected with the WAH high‐quality calving pixels to produce a weighted set of high‐quality pixels, in which pixels that had been used more frequently for WAH calving received a higher weight (Fig.…”

“…S1): Alternative A-the no-action alternative-maintained the existing land use and management restrictions from the 2013 IAP (about 52% of the subsurface available for oil and gas development), Alternative B slightly increased the area made unavailable for leasing and altered its configuration (50% available), Alternative C expanded the area available for development, especially around Teshekpuk Lake and in the Brooks Range foothills (75% available), and Alternative D greatly expanded the area available for development (81% available), including nearly all land around Teshekpuk Lake. In addition to the four alternatives (Person et al 2007, Cameron et al 2020. Existing roads are sparse within the NPR-A and include both those already completed (CD5, Greater Mooses Tooth 1 [GMT1]) and those under construction (GMT2).…”