Demographic responses of bighorn sheep to recreational activities: A trial of a trail

Abstract

Long‐term effects of anthropogenic disturbance to wildlife, and whether such effects have population‐level consequences, often are difficult to determine. In 1996, a recreational hiking trail (Maah Daah Hey Trail [Trail]) was constructed by the U.S. Forest Service through 4 geographic areas, each occupied by a distinct sub‐population of bighorn sheep (Ovis canadensis), in western North Dakota, USA. From 2001 to 2012, we monitored distribution, recruitment rates, and abundance of female bighorn sheep in the sub‐populations to investigate responses to activities associated with the Trail, and whether demographic consequences occurred. Female bighorn sheep at Sully Creek were displaced from, and eventually abandoned, lambing habitat subjected to intensive recreational use that was erratic and unpredictable. Consequently, females inhabiting Sully Creek had lower fidelity to lambing areas than did other sub‐populations, all of which realized 100% fidelity. Further, females inhabiting Sully Creek achieved lower recruitment of young, exhibited a substantial downward trend in recruitment rate, and a decline in abundance of females compared with the other sub‐populations also exposed to the Trail, but where perturbation was less severe and human activities were consistent, predictable, and spatial separation existed between recreationists and lambing habitat. Metapopulations of bighorn sheep occurring in fragmented habitat having minimal vertical relief may be especially susceptible to sources of disturbance, which should be a consideration when recreational facilities are developed. © 2014 The Wildlife Society.

Ecotypic variation in population dynamics of reintroduced bighorn sheep

“…Most precipitation occurred during April-September (Jensen 1974). Precipitation records from the 5 weather stations in our study area were strongly correlated (all r > 0.90), as were temperature records (all r > 0.99; Wiedmann and Bleich 2014). Monthly temperatures at Medora, North Dakota, ranged from À378C to >418-C (annual x ¼ 7.43 AE 14.768C [SD]), with average high and low temperatures during our investigation of 30.58C and À178C in July and January, respectively (Western Regional Climate Center 2016).…”

“…As a result, use of translocation stock best adapted to a particular area, especially when combined with knowledge of recruitment rates and adult survival, likely is advantageous when evaluating or mitigating anthropogenic effects on bighorn sheep on the eastern fringe of their geographic distribution in North Dakota. Among these effects are energy development (Dyke et al , Christie et al ), recreational use of bighorn sheep range (Wiedmann and Bleich ), reestablishment and expansion of mountain lions (Wilckens et al ), and an abundance of coyotes (Tucker ).…”

“…We used a hand‐held net‐gun fired from a helicopter to capture individual bighorn sheep (Krausman et al ) except in 2014, when we used a drop‐net to capture bighorn sheep in Alberta, Canada. Marked bighorn sheep included individuals captured from herds throughout our study area (Wiedmann and Bleich , Wiedmann and Sargeant ) and bighorn sheep translocated to North Dakota from Oregon, USA (2003 and 2004), Montana (2006 and 2007), and Alberta (2014). We marked captured bighorn sheep with very high frequency radio‐telemetry collars equipped with mortality sensors, which we used to monitor survival from 3 November 2000 to 14 May 2016.…”

Determining Timing of Births and Habitat Selection to Identify Lambing Period Habitat for Bighorn Sheep

“…After giving birth, female bighorns generally form nursery groups with other females and young in rugged areas of high elevation and steep slopes (Geist, 1971;Bangs et al, 2005;Karsch et al, 2016). These groups then move cohesively among patches of nursery habitat for the subsequent months (Bangs et al, 2005;Whiting et al, 2012;Wiedmann and Bleich, 2014). In general, Rocky Mountain bighorn sheep (O. c. canadensis) give birth later in spring, and the birthing period is constricted allowing females to exploit the shortened growing season during summer (Bunnell, 1982;Thompson and Turner, 1982).…”

“…In an area that was intentionally disturbed by humans during parturition, counts of young/female elk (Cervus canadensis) were 22.5% lower than in areas with undisturbed herds (Phillips and Alldredge, 2000). Populations of bighorn sheep can be negatively influenced by anthropogenic disturbances, especially during the birthing season (Papouchis et al, 2001;Wiedmann and Bleich, 2014;Smith et al, 2015). These disturbances can cause females to abandon previously used nursery habitat.…”