Abstract
BackgroundCaribou in the Western Arctic Herd undertake one of the longest, remaining intact migrations of terrestrial mammals in the world. They are also the most important subsistence resource for many northern rural residents, who rely on the caribou’s migratory movements to bring them near for harvest. Migratory geography has never been static, but subsistence harvesters have reported recent shifts in migration away from areas where they traditionally occurred. The reasons behind these changes are not well-understood, but may be related to rapid climate change and anthropogenic disturbances.MethodsTo predict changes in distribution and shifting migratory areas over the past decade, we used GPS telemetry data from adult females to develop predictive ecological niche models of caribou across northwestern Alaska. We employed the machine-learning algorithm, TreeNet, to analyze interactive, multivariate relationships between telemetry locations and 37 spatial environmental layers and to predict the distributions of caribou during spring, calving season, insect-harassment season, late summer, fall, and winter from 2009 to 2017. Model results were analyzed to identify regions of repeated predicted use, quantify mean longitude, predict land cover selection, and track migratory changes over time.ResultsDistribution models accurately predicted caribou at a spatially-explicit, 500-m scale. Model analyses identified migratory areas that shifted annually across the region, but which predicted 4 main areas of repeated use. Niche models were defined largely by non-linear relationships with coastally-influenced, climatic variables, especially snow-free date, potential evapo-transpiration, growing season length, proximity to sea ice, winter precipitation and fall temperature. Proximity to roads and communities were also important and we predicted caribou to generally occur more than 20–100 km from these features.ConclusionsWestern Arctic Herd caribou were predicted to occur in warmer, snow-free and treeless areas that may provide conditions conducive for efficient travel and foraging. Rapidly changing seasonal climates and coastal influences that determine forage availability, and human impediments that slow or divert movements are related to geographically and phenologically dynamic migration patterns that may periodically shift caribou away from traditional harvest areas. An enhanced understanding of the geographic behavior of caribou over time could inform traditional harvests and help conserve important Western Arctic caribou migratory areas.
Highlights
Caribou in the Western Arctic Herd undertake one of the longest, remaining intact migrations of terrestrial mammals in the world
Data collection Over the past decade, 211 adult female caribou belonging to the Western Arctic Herd (WAH) were captured in Kobuk Valley National Park, Alaska and fitted with Global Positioning System (GPS) telemetry collars (Telonics TGW-4680, Mesa, Arizona, USA) following protocols approved by a State of Alaska Institutional Animal Care and Use Committee (IACUC 0040–2017-40) [33]
Models generally predicted caribou to occur in areas where mean decadal fall temperatures were above − 4 °C (Fig. 2c) and where average snow melt occurred between April 20 and May 10 (Fig. 2d)
Summary
Caribou in the Western Arctic Herd undertake one of the longest, remaining intact migrations of terrestrial mammals in the world They are the most important subsistence resource for many northern rural residents, who rely on the caribou’s migratory movements to bring them near for harvest. Impediments to movement include barriers such as transportation corridors [16,17,18,19], fences [8], urban and industrial development [20, 21], unavailable forage and habitat [5], and unstable ice and snow conditions [22,23,24] These obstacles cause animals to expend additional time and energy to navigate. Because migration routes are difficult to restore once interrupted, identifying and conserving important migratory areas should be a top priority for land managers [7, 18, 25]
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