Short-Term Impacts of Military Overflights on Caribou During Calving Season

The Fortymile Caribou Herd (FCH) is the most prominent caribou herd in interior Alaska. A large portion of the FCH calving and summer range lies beneath heavily used Military Operations Areas (MOA) that are important for flight training. We observed the behavior of Grant’s cow caribou (Rangifer tarandus granti) and their calves before, during, and immediately following low-level military jet overflights. We also monitored movements of radiocollared cow caribou and survival of their calves. We conducted fieldwork from mid May through early June 2002. We concluded that military jet overflights did not cause deaths of caribou calves in the FCH during the calving period nor result in increased movements of cow–calf pairs over the 24-hour period following exposure to overflights. Short-term responses to overflights were generally mild in comparison to caribou reactions to predators or perceived predators. Caribou responses to overflights were variable, but responses were generally greater as slant distances decreased and jet speeds increased. A-10 jets caused less reaction than F-15s and F-16s. Although we found that short-term reactions of caribou to jet overflights were mild, we advise against assuming there are no long-term effects on calving caribou from jet overflights

Modeling Caribou Movements: Seasonal Ranges and Migration Routes of the Central Arctic Herd.

Migration is an important component of the life history of many animals, but persistence of large-scale terrestrial migrations is being challenged by environmental changes that fragment habitats and create obstacles to animal movements. In northern Alaska, the Central Arctic herd (CAH) of barren-ground caribou (Rangifer tarandus granti) is known to migrate over large distances, but the herd's seasonal distributions and migratory movements are not well documented. From 2003-2007, we used GPS radio-collars to determine seasonal ranges and migration routes of 54 female caribou from the CAH. We calculated Brownian bridges to model fall and spring migrations for each year and used the mean of these over all 4 years to identify areas that were used repeatedly. Annual estimates of sizes of seasonal ranges determined by 90% fixed kernel utilization distributions were similar between summer and winter (X̅ = 27,929 SE = 1,064 and X̅ = 26,585 SE = 4912 km2, respectively). Overlap between consecutive summer and winter ranges varied from 3.3-18.3%. Percent overlap between summer ranges used during consecutive years (X̅ = 62.4% SE = 3.7%) was higher than for winter ranges (X̅ = 42.8% SE = 5.9%). Caribou used multiple migration routes each year, but some areas were used by caribou during all years, suggesting that these areas should be managed to allow for continued utilization by caribou. Restoring migration routes after they have been disturbed or fragmented is challenging. However, prior knowledge of movements and threats may facilitate maintenance of migratory paths and seasonal ranges necessary for long-term persistence of migratory species

Relative use of migration routes by the Central Arctic caribou herd in northern Alaska, 2003–2007.

<p>(A) spring (B) fall. Use of 500-m grid cells was estimated as the mean of Brownian Bridge Movement Models for each year. Contours enclose portions of the UD with corresponding levels of use (i.e., 25% contour encloses 25% of the UD with the highest probability of use).</p

Numbers of migratory and non-migratory female caribou who met the definition of migration from the Central Arctic herd monitored in northern Alaska by season, 2003–2007.

<p>Numbers of migratory and non-migratory female caribou who met the definition of migration from the Central Arctic herd monitored in northern Alaska by season, 2003–2007.</p

Mean annual start and end dates of seasons classified by caribou movement characteristics estimated for fall and spring migrations of the Central Arctic caribou herd in northern Alaska, 2003–2007.

<p>Summer extended from the end of calving to the beginning of fall migration; winter extended from the end of fall migration to the beginning of spring migration.</p

Study area in northern Alaska including the Dalton highway, the Trans-Alaska Pipeline (TAP), major land ownership divisions, and rivers mentioned in text.

<p>Study area in northern Alaska including the Dalton highway, the Trans-Alaska Pipeline (TAP), major land ownership divisions, and rivers mentioned in text.</p

Years of use of seasonal ranges of the Central Arctic caribou herd in northern Alaska, 2003–2007.

<p>(A) summer ranges. (B) winter ranges. Ranges were modeled as the 90% isopleths of fixed-kernel utilization distributions for each season and year. Shading indicates the number of years each area was used (i.e., number of intersections of the 4 annual ranges modeled for each season).</p

Percent of the total area of summer and winter ranges used during multiple years by caribou of the Central Arctic herd in northern Alaska, 2003–2006.

<p>Total area was the aggregate of 90% fixed kernel UDs estimated for all years (39,966 and 57,457 km² for summer and winter range, respectively).</p

Number of years of use of seasonal migration routes by the Central Arctic caribou herd in northern Alaska, 2003–2007.

<p>(A) spring (B) fall. Each route was defined as the mean of the 95% isopleths of the Brownian Bridge Movement Models of all caribou for each season.</p