Aerial survey and telemetry data analysis of a peripheral caribou calving area in northwestern Alaska

With industrial development expanding in the Arctic, there is increasing interest in quantifying the impacts of development projects on barren ground caribou (Rangifer tarandus granti). The primary data source to assess caribou distribution and predict impacts in remote areas of Alaska has shifted in recent decades from aerial survey data to telemetry data, but these techniques have different strengths and weaknesses. The ranges of two caribou herds, the Western Arctic Herd and the Teshekpuk Herd, overlap in northwest Alaska between Wainwright and Atqasuk, Alaska. Based on long-term telemetry data sets, this region was thought to be outside of the core calving ranges of both herds. Calving has long been reported to occur in this general area, but early reports assumed caribou were from the Western Arctic Herd and only one systematic aerial survey of caribou density and distribution during calving has been conducted in this area in recent decades. Following interest in industrial development in this area, we conducted aerial strip-transect surveys during early to mid-June 2013–2015 to directly assess the density and distribution of caribou in the area and we used existing telemetry data to compare our results to the seasonal distribution of both herds. Total caribou densities varied between 0.36 and 1.06 caribou/km² among years, and calf densities varied 0.04 and 0.25 calves/km² among years. Contrary to assumptions by early researchers in the area, telemetry data indicated that caribou in this area during early to mid-June were from the Teshekpuk Herd. The use of telemetry data alone underestimated the importance of this area for calving, but the combination of aerial surveys and telemetry data provided complementary information on caribou use of this area showing the importance of collecting the appropriate types of data for assessing potential impacts of development on caribou

Calving distribution of the Teshekpuk caribou herd, 1994-2003

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

Predation on Caribou (Rangifer tarandus) by Wolverines (Gulo gulo) after long pursuits

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

Efficacy of calf:cow ratios for estimating calf production of arctic caribou

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

Calving distribution of the Teshekpuk caribou herd, 1994-2003

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

Movement-based methods to infer parturition events in migratory ungulates

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 2 movement-based methods developed to infer parturition in non-migratory 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 (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 inter-annual variation ranging from 61-100%. When we considered instances when the 2 analytical methods agreed on parturition outcome, the accuracy increased to 89% with an annual range of 73-100%. Using these methods, we identified marked inter-annual 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.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Summer resource selection and identification of important habitat prior to industrial development for the Teshekpuk Caribou Herd in northern Alaska.

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

Relative probability of use during high and low insect harassment periods.

<p>Predicted maps derived from landscape-scale resource selection function results for the Teshekpuk Caribou Herd in Alaska based on data from 2004–2010: (A) high mosquito harassment, (B) low mosquito harassment, (C) high oestrid fly harassment, and (D) low oestrid fly harassment. Blue pixels represent areas with water where resource selection was not measured. The predicted map’s extent is defined by the range of the herd during the mosquito harassment period (A-B) and the oestrid fly harassment period (C-D).</p

Relative probability of use for parturient and non-parturient females during calving.

<p>Map of relative probability of use during the calving period for (A) parturient and (B) non-parturient females of the Teshekpuk Caribou Herd derived from landscape-scale resource selection function results on data from 2004–2010. Blue pixels represent areas with water where resource selection was not measured. The predicted map’s extent is defined by the range of the herd during the calving period.</p