Migration patterns of pronghorn in southwestern North Dakota

Abstract

Wildlife managers need empirical data about pronghorn (Antilocapra americana) movements in North Dakota to assess whether mid‐summer surveys represent occupancy of pronghorn in hunting units during the fall hunting season. Using data from 121 radiocollared pronghorn we evaluated patterns of pronghorn migrations in southwestern North Dakota from 2004 to 2007. Pronghorn exhibited 2 primary movement patterns between summer and winter ranges: migrations >15 km (45%) and movement <15 km (55%). Most migratory pronghorn moved northeast or east in the spring and southwest or west in the fall. Average distance moved for migratory pronghorn was 70.6 km (range = 17.4–253 km). Mean date of pronghorn migration in spring was 20 March (SD = 20 days) and in fall was 22 October (SD = 17 days). Nearly all migratory pronghorn (97%) returned to within 15 km of their previous summer range, whereas only 61% of pronghorn returned to within 15 km of their previous winter range. Most pronghorn moved across hunting and survey unit boundaries; however, only 7 fall migrations occurred between the aerial survey and the hunting season. During years of our study, the mid‐summer survey provided representative information about hunting unit occupancy of radiocollared pronghorn for the fall hunting season. © 2011 The Wildlife Society

Seasonal Distribution and Routes of Pronghorn in the Northern Great Basin

“…Typically, outside of elevational-related migration, pronghorn generally move north in the spring and south in the fall to warmer winter ranges (Sawyer et al 2005, Sheldon and Lindzey 2006, Kolar et al 2011). In contrast, pronghorn in the northern Great Basin demonstrated wide variation in directional movements between seasonal ranges and between years.…”

“…The proportion of pronghorn that migrated in this study ranged from 65% in 2011/2012 to 100% in 2012/2013 during harsher winter conditions; although the majority also made exploratory movements during fall 2011. Pronghorn may avoid adverse conditions by differing their migration strategy across years (e.g., Bruns 1977, Hoskinson and Tester 1980, Barrett 1984, Kolar et al 2011. The proportion of migratory individuals within a population can vary greatly among regions, ranging from 8%-19% (Jacques et al 2009b) to 70%-81% of individuals migrating annually (White et al 2007).…”

“…Subsequently, only 2 individuals made long-distance exploratory movements during the fall 2012 migration period before settling on their respective winter ranges. Kolar et al (2011) hypothesized that milder winters (i.e., warmer temperatures with less snow cover) would result in decreased migration distances. This hypothesis is supported by findings in this study where during 2012/2013, fall migration distances were longer with fewer exploratory movements compared to distances observed during 2011/2012 in more mild winter conditions.…”

“…Exploratory movements were defined as movements observed during the fall migration period in which the individuals did not travel directly toward their eventual winter range, but initially traveled away from or bypassed through the wintering area before returning. I defined individual migration start dates as the first location that deviated ≥5 km from a seasonal range and was associated with successive directional movements (Kolar et al 2011). To omit locations associated with migration or exploratory movements from seasonal range calculations, I defined seasonal ranges (winter and summer) as the time period 1 day after the last marked animal's arrival date to 1 day prior to the first marked animal's departure date.…”

Classifying the migration behaviors of pronghorn on their northern range

“…In addition, 30 individuals made round‐trip migrations of ≥200 km, which exceed distances reported in previous pronghorn studies (Berger ). Comparatively, in Wyoming, pronghorn made spring migrations between 82 km and 177 km (Sawyer et al , Sheldon ); in North Dakota, mean spring migration was 75 km and fall migration was 63 km (Kolar et al ), whereas in Idaho, pronghorn migrated a mean distance of 44 km (Hoskinson and Tester ). Our mean migration distances exceed those of Sonoran pronghorn ( A. a. sonoriensis ) at the southern periphery of the species range that moved 42 km when traveling to and from summer ranges and as much as 130 km within home ranges from cool‐season to hot‐season habitats (O'Gara , Hervert et al ).…”