The Influence of Mountain Lion Predation on Bighorn Sheep Translocations

Abstract

We studied the effects of mountain lion (Puma concolor) predation on 2 translocated populations of bighorn sheep (Ovis canadensis) in New Mexico, USA. During 1993, 32 Rocky Mountain bighorn sheep (O. c. canadensis) were translocated to Wheeler Peak Wilderness Area in northern New Mexico, and during 1992–1993, 31 desert bighorn sheep (O. c. mexicana) were translocated to Sierra Ladron in central New Mexico. We monitored both populations from release through 2000 using fixed‐wing aircraft and ground and/or helicopter surveys. We determined cause of mortality for radiomarked individuals (n = 26) and calculated survival rates, cause‐specific mortality rates, exponential growth rates, and lamb:ewe ratios. The post‐lambing population estimates in 2000 were 180 in Wheeler Peak and 21 in Sierra Ladron. Annual adult survival was higher (P < 0.005) in the Wheeler Peak population (0.955) than in the Sierra Ladron population (0.784). Annual lamb:ewe ratios also were higher (P < 0.001) in the Wheeler Peak population (66.7 vs. 29.8). Mean annual exponential growth rate (r) in the Wheeler Peak population was 0.25 compared to −0.01 for the Sierra Ladron population. Predation by mountain lions was the primary proximate cause (75%) of 16 known‐cause mortalities of radiomarked bighorn sheep in the Sierra Ladron population, while we did not document any predation in Wheeler Peak. The annual cause‐specific mortality rates due to mountain lion predation in Sierra Ladron were 0.13 for males, 0.09 for females, and 0.11 for all adult bighorn sheep. Mountain lion predation may have limited the Sierra Ladron bighorn sheep population and could be imposing a destabilizing inverse density‐dependent mortality. Mountain lions preyed on domestic cattle in the Sierra Ladron area and throughout desert bighorn sheep habitat in New Mexico; we therefore hypothesize that cattle “subsidized” the diets of mountain lions (i.e., reduced or eliminated natural starvation). The ultimate cause of mortality for these desert bighorn sheep may be related to subsidized mountain lion populations that do not appear to decline following native ungulate population decreases. In addition, the encroachment of woody vegetation may increase the hunting success of ambush predators like mountain lions. High mountain lion predation may require mitigation for the successful restoration of bighorn sheep.

Effects of Simulated Mountain Lion Caching on Decomposition of Ungulate Carcasses

“…Although a recent review of research regarding mule deer population declines concluded that mountain lions probably have had major impacts only where deer populations were severely reduced for other reasons (Ballard et al 2001), and where lions have had significant numbers of alternate prey, an influential constituency still exists for widespread reduction of lion populations to increase densities of mule deer. Even greater support exists among hunters and wildlife managers for reducing or eliminating mountain lions in limited areas to help recover or re-establish bighorn sheep populations, supported by recent research showing that mountain lions were a significant factor in the loss or near loss of several populations of desert bighorn sheep (Hayes et al 2000, Rominger et al 2004.…”

“…Times and locales preferred for hunting are clearly relevant to assessing and managing the risks to humans that are increasingly of concern to managers. Under certain circumstances, mountain lion predation can limit bighorn sheep (Ovis canadensis), have potentially deleterious impacts on vulnerable pronghorn (Antilocapra americana), and potentially regulate mule deer (Odocoileus hemionus) and other ungulate populations (Ockenfels 1994, Hayes et al 2000, Logan and Sweanor 2001, Robinson et al 2002, Rominger et al 2004). These direct effects on populations of herbivores potentially translate into indirect effects on vegetation structure and composition (Ripple and Beschta 2006).…”

The difference between killing and eating: ecological shortcomings of puma energetic models

“…Estimates of kill rates have increased our understanding of dynamic species interactions in complex multispecies communities, including apparent competition affecting rare prey (Holt andLawton 1994, Wittmer et al 2013), predation-mediated Allee effects (McLellan et al 2010), and the effects of kleptoparasitism on the fitness of subordinate competitors (Gorman et al 1998, Elbroch andWittmer 2013a). Accurate estimates of kill rates are also essential for managers charged with setting sustainable harvest quotas for game species coexisting with native predators (e.g., White and Lubow 2002), and developing conservation strategies for species negatively affected by predation, including those in reintroduction programs (e.g., Rominger et al 2004.…”

Subsidized predators, landscapes of fear and disarticulated carnivore communities

“…Such scenarios become problematic for conservation practitioners when the enhanced predator population influences species of conservation concern. Examples of this are widespread: subsidized ravens influence tortoise ecology (Boarman, 2003); subsidized predatory beetles influence insect herbivore populations (Rand & Louda, 2006); subsidized mountain lions influence bighorn sheep demographics (Rominger et al, 2004); and in the example presented by Shapira, Sultan & Shanas (2008), subsidized red foxes Vulpes vulpes influence gerbil ecology.…”