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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.

Ungulates are an important source of food for Wolverines (Gulo gulo), especially in winter when scavenging on carcasses is a primary means of obtaining food. However, Wolverines are also known to prey on ungulates. We followed fresh tracks of Wolverines pursuing Caribou (Rangifer tarandus) on six occasions on the tundra of northern Alaska in 2011, 2015, 2017, and 2018; all ended in a predation event after pursuits of 4−62 km. Exhaustion of the Caribou after long pursuits appeared to contribute to the success of predation attempts. Snow conditions appeared to be a factor in only one of the six cases.

Long-distance migrations by ungulate species are a globally imperiled natural phenomenon and conservation of them requires monitoring population vital rates. Satellite telemetry tracking is widely used for understanding the spatial distribution and movement of animals, especially migratory animals in remote environments. Recently, analytical methods have been developed to infer parturition events from movement data in multiple species that calve in isolation, but to date such methods have not been tested on animals that both migrate and spatially aggregate during calving. We applied two movement-based methods developed to infer parturition in nonmigratory woodland caribou (Rangifer tarandus caribou (Gmelin, 1788)) to 241 reproductive seasons spanning 6 years of GPS data from migratory barren-ground caribou (Rangifer tarandus granti J.A. Allen, 1902). We compared results from both methods to data from aerial surveys of collared females during the calving period. We found that each movement-based method had ∼80% overall accuracy to identify calving events, with interannual variation ranging from 61% to 100%. When we considered instances when the two analytical methods agreed on parturition outcome, the accuracy increased to 89% with an annual range of 73%–100%. Using these methods, we identified marked interannual differences in peak calving dates and higher parturition rates than previously reported for this caribou herd. The successful application of these analyses to a migratory, gregarious ungulate suggests a broader applicability of the methodology.

Long distance migrations by large mammals are increasingly imperiled by human development. We studied autumn migratory patterns of caribou (Rangifer tarandus) in relation to an industrial road in northwestern Alaska. We built null movement models to determine the expected time to cross the road if caribou movements were not affected by the road. We then identified individuals that took longer to cross than expected (slow crossers) and those that did not differ from that expected from the null model (normal crossers). We identified eight as slow and 20 as normal crossers. Slow crossers took an average of 33.3 ± 17.0 (± SD) days to cross the road compared to 3.1 ± 5.5 days for normal crossers. Slow crossers had an average crossing date of 8 Nov. ± 7.7 days versus 25 Oct. ± 20.6 days for normal crossers. Movement rates of the two classes did not differ before crossing the road, but slow crossers moved > 1.5 times as fast as normal crossers after crossing the road. Movement patterns were partially explained by environmental attributes, but were most strongly affected by how far a caribou was from the road and whether it was classified as slow or normal crosser. While avoidance is an important aspect of the effects of roads on populations, our results show the importance of other factors, such as how long individuals are delayed in crossing when assessing the influence of development on wildlife.

There is a trade-off between the frequency of telemetry locations (fix interval) and battery life when using Global Positioning System (GPS) collars. In general, decreasing the fix interval lowers the effective battery life of the collar. However, the strong relationship between fix interval and movement metrics is often underappreciated. Mean movement rates, maximum movement rates, total distance estimates, and some screening algorithms change dramatically with different fix intervals, particularly for highly mobile animals such as caribou (Rangifer tarandus), and must be interpreted in relation to the fix interval used to collect the data. We used a multi-year, high-resolution data set from GPS collars with 2-hr fix intervals deployed on female caribou of the Teshekpuk Caribou Herd, Alaska, USA, 2006–2011, to examine the effect of fix interval on estimates of movement metrics. By calculating straight-line distances between locations taken at different fix intervals, we examined the rate of change in various metrics of caribou movement as a function of fix interval. We also calculated correction factors for different fix intervals, and examined how they changed seasonally. We fit an equation to the maximum rate of movement of caribou as a function of fix interval and used this equation in a modification of one screening algorithm to assess how it is affected by fix interval. We demonstrate how the maximum speed equation could potentially be used to derive a modified filter for telemetry data from highly mobile animals. Our results highlight the importance of incorporating fix-interval information into comparisons of movement metrics from different herds and time periods. © 2013 The Wildlife Society.

USO DE UNA PISTOLA DE RED PARA CAPTURAR DE MODO SEGURO A INDIVIDUOS DE ASIO FLAMMEUS EN VUELO DESDE UN HELICOPTERO Probamos una tecnica novedosa de captura que consiste en disparar desde un helicoptero una red sobre individuos de Asio flammeus en vuelo, para colocar transmisores satelitales en esta especie en disminucion. Capturamos 18 buhos (10 machos, 8 hembras) durante 17 horas de vuelo y colocamos transmisores en 12 aves que cumplieron con nuestro criterio de uso de transmisores. Desplegamos 2.5 ± 1.0 redes por captura exitosa, con una moda de una red por captura. Las persecuciones duraron 4.0 ± 4.1 min. No se mato ningun buho y no se detectaron heridas considerables como huesos rotos, abrasiones o contusiones. Todas las aves a las que se les colocaron los transmisores sobrevivieron al menos tres semanas luego de la captura; 10 de las 12 aves migraron hasta 5500 km. Hemos demostrado, por primera vez, el uso seguro de redes disparadas desde helicopteros para capturar aves en vuelo. Recomendamos el uso ...

Caribou (Rangifer tarandus granti) calf:cow ratios (CCR) computed from composition counts obtained on arctic calving grounds are biased estimators of net calf production (NCP, the product of parturition rate and early calf survival) for sexually-mature females. Sexually-immature 2-year-old females, which are indistinguishable from sexually-mature females without calves, are included in the denominator, thereby biasing the calculated ratio low. This underestimate increases with the proportion of 2-year-old females in the population. We estimated the magnitude of this error with deterministic simulations under three scenarios of calf and yearling annual survival (respectively: low, 60 and 70%; medium, 70 and 80%; high, 80 and 90%) for five levels of unbiased NCP: 20, 40, 60, 80, and 100%. We assumed a survival rate of 90% for both 2-year-old and mature females. For each NCP, we computed numbers of 2-year-old females surviving annually and increased the denominator of CCR accordingly. We then calculated a series of hypothetical “observed” CCRs, which stabilized during the last 6 years of the simulations, and documented the degree to which each 6-year mean CCR differed from the corresponding NCP. For the three calf and yearling survival scenarios, proportional underestimates of NCP by CCR ranged 0.046–0.156, 0.058–0.187, and 0.071–0.216, respectively. Unfortunately, because parturition and survival rates are typically variable (i.e., age distribution is unstable), the magnitude of the error is not predictable without substantial supporting information. We recommend maintaining a sufficient sample of known-age radiocollared females in each herd and implementing a regular relocation schedule during the calving period to obtain unbiased estimates of both parturition rate and NCP.

Many caribou (Rangifer tarandus) populations are declining worldwide in part due to disturbance from human development. Prior to human development, important areas of habitat should be identified to help managers minimize adverse effects. Resource selection functions can help identify these areas by providing a link between space use and landscape attributes. We estimated resource selection during five summer periods at two spatial scales for the Teshekpuk Caribou Herd in northern Alaska prior to industrial development to identify areas of high predicted use for the herd. Additionally, given the strong influence parturition and insect harassment have on space use, we determined how selection differed between parturient and non-parturient females, and between periods with and without insect harassment. We used location data acquired between 2004–2010 for 41 female caribou to estimate resource selection functions. Patterns of selection varied through summer but caribou consistently avoided patches of flooded vegetation and selected areas with a high density of sedge-grass meadow. Predicted use by parturient females during calving was almost entirely restricted to the area surrounding Teshekpuk Lake presumably due to high concentration of sedge-grass meadows, whereas selection for this area by non-parturient females was less strong. When insect harassment was low, caribou primarily selected the areas around Teshekpuk Lake but when it was high, caribou used areas having climates where insect abundance would be lower (i.e., coastal margins, gravel bars). Areas with a high probability of use were predominately restricted to the area surrounding Teshekpuk Lake except during late summer when high use areas were less aggregated because of more general patterns of resource selection. Planning is currently underway for establishing where oil and gas development can occur in the herd’s range, so our results provide land managers with information that can help predict and minimize impacts of development on the herd.

Parturient female caribou from the Teshekpuk caribou (Rangifer tarandus granti) herd (TCH) have been observed across the western North Slope, but most cows that were seen with calves during the calving period were in the area surrounding Teshekpuk Lake. During surveys conducted between 1994 and 2003, 155 (91%) of 171 collared cows seen with calves were within an area given protected status in the 1998 Bureau of Land Management Final Integrated Activity Plan/Environmental Impact Statement (IAP/EIS). The percentage of adult collared cows seen with a calf between 1994 and 2003 has ranged from 44% to 86%, with a mean of 66%. The years with the lowest percentage of collared cows seen with calves were 1997 (50%) and 2001 (44%). In 1997 most of the herd migrated much farther south than usual, and in 2001 unusually deep, persistent snow restricted spring migration, resulting in fewer cows returning to the traditional calving area during the calving period. When snowmelt dates were earlier, calving locations were farther north. Average standardized travel rates for parturient cows were significantly greater before they had calves (7.25 km/day) than after 3.89 (km/day). Geographically, protections granted by the 1998 BLM IAP/EIS appear to adequately cover the concentrated calving grounds, allowing for variance in the annual distribution of calving cows.