Variation in winter site fidelity within and among individuals influences movement behavior in a partially migratory ungulate.

Timothy J Fullman,Lincoln S Parrett,Brian T Person,Alexander K Prichard,Marco Apollonio

doi:10.1371/journal.pone.0258128

Timothy J Fullman, Lincoln S Parrett + Show 3 more

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https://doi.org/10.1371/journal.pone.0258128

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Abstract

Many animals migrate to take advantage of temporal and spatial variability in resources. These benefits are offset with costs like increased energetic expenditure and travel through unfamiliar areas. Differences in the cost-benefit ratio for individuals may lead to partial migration with one portion of a population migrating while another does not. We investigated migration dynamics and winter site fidelity for a long-distance partial migrant, barren ground caribou (Rangifer tarandus granti) of the Teshekpuk Caribou Herd in northern Alaska. We used GPS telemetry for 76 female caribou over 164 annual movement trajectories to identify timing and location of migration and winter use, proportion of migrants, and fidelity to different herd wintering areas. We found within-individual variation in movement behavior and wintering area use by the Teshekpuk Caribou Herd, adding caribou to the growing list of ungulates that can exhibit migratory plasticity. Using a first passage time–net squared displacement approach, we classified 78.7% of annual movement paths as migration, 11.6% as residency, and 9.8% as another strategy. Timing and distance of migration varied by season and wintering area. Duration of migration was longer for fall migration than for spring, which may relate to the latter featuring more directed movement. Caribou utilized four wintering areas, with multiple areas used each year. This variation occurred not just among different individuals, but state sequence analyses indicated low fidelity of individuals to wintering areas among years. Variability in movement behavior can have fitness consequences. As caribou face the pressures of a rapidly warming Arctic and ongoing human development and activities, further research is needed to investigate what factors influence this diversity of behaviors in Alaska and across the circumpolar Arctic.

Highlights

MethodsStudy area and speciesThe Teshekpuk Caribou Herd (TCH) is one of four caribou herds that calve on the North Slope of Alaska, along with the Western Arctic Herd, Central Arctic Herd, and Porcupine Caribou Herd
Migration is a widely exhibited behavior among diverse taxa, including invertebrates, birds, mammals, reptiles, and fish [1,2,3,4]
After comparing results of the four approaches, we found only the first passage time–net squared displacement approach (FPT-NSD) suitable for our purposes of characterizing caribou movement and identifying seasonal use

Summary

Methods

Study area and speciesThe TCH is one of four caribou herds that calve on the North Slope of Alaska, along with the Western Arctic Herd, Central Arctic Herd, and Porcupine Caribou Herd. The herd primarily calves around Teshekpuk Lake in northwestern Alaska (Fig 1) [30,31,32], though some calving has been noted farther west [34]. The herd clusters along the coast and in riparian areas seeking relief from mosquitoes (Culex spp.) and oestrid flies (Hypoderma spp. and Cephenemyia spp.) before spreading out to forage across the arctic coastal plain [30,31]. Unlike the other three large migratory herds in northern Alaska, the majority of the TCH remains on the coastal plain year-round [30,35]. Some TCH caribou remain resident near Teshekpuk Lake, others make a relatively short-distance migration to wintering areas on the western coastal plain, while part of the herd migrates from the coastal plain to overwinter in the Brooks Range mountains and areas farther south [30]

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