Elk populations in the Bitterroot Valley in western Montana have been monitored since the mid-1960s. From the mid-1960s until 2003, elk numbers steadily increased.
In 2004, FWP increased antlerless harvests to reduce elk population numbers toward management objective. Since 2004, however, cow:calf ratios have declined throughout the valley to just 14 calves per 100 cows, including a valley-wide historic low in elk calf recruitment in 2009.
Further, some populations in the valley, such as the West Fork of the Bitterroot, have substantially declined. In 2008-2010, elk counts of 744-863 were 46-54% below the minimum population objective of 1,600 elk for the West Fork EMU and recruitment rates were only 9-11 calves per 100 cows. Low recruitment and population declines have raised public concerns that the increasing number of wolves may be reducing elk populations and hunter opportunities in the Bitterroot Valley.
While basic factors like density-dependence may decrease recruitment rates, recent declines in elk counts and recolonization by dense wolf populations suggest predation may be playing a role. The management issue of wolf effects on ungulate prey is a priority issue for FWP across Montana as wolf recovery continues. FWP biologists are faced with the challenge of managing these elk populations without an understanding of the factors limiting calf recruitment. The relative effects of bottom-up and top-down influences on elk populations and recruitment are unknown, making implementation of effective management actions difficult.
Potential causes of elk population declines and reduced recruitment may include poor maternal body condition, reduced pregnancy rates, and/or increases in calf predation. Elk populations have increased during the past 20 years, and if populations have approached nutritional carrying capacity, reductions in maternal body condition and pregnancy rates may have contributed to reductions in recruitment. Further, habitat differences between herds may result in underlying differences in productivity and recruitment. Restoration of wolves may have also contributed to reduced recruitment. In addition to the healthy black bear and mountain lion populations in the Bitterroot, wolves recolonized the area in 2000 and the wolf populations grew to 11 packs (45-60 individuals) in 2009. The addition of wolves to the system may also have contributed to a reduction in survival and recruitment rates. While recent syntheses of elk calf survival studies across the Pacific Northwest showed wolves play a relatively minor role in neonatal calf survival, a remaining unknown is the degree to which winter calf mortality is caused by wolves and how this interacts with bottom-up factors.
The purpose of this project is to test for relative effects of maternal nutritional condition and predation on elk productivity, survival, and recruitment. The probability of pregnancy, over-winter survival, lactation yields, and susceptibility to predation influence elk survival and reproduction and are related to maternal nutritional conditional. Previous FWP research evaluating the role of predation in limiting or regulating elk populations concluded that predator-prey interactions may be landscape dependent and predators may limit elk populations when high predator prey ratios are reached. Building from these previous studies, our main research objectives are to test the following two competing hypotheses:
Results of this research will be used to guide management actions in the Bitterroot Valley of western Montana and throughout the Northern Rockies where wolf recolonization is occurring. Specifically, estimating baseline rates of elk productivity and predator offtake will provide information on the role of predators in regulating the elk population, allow biologists to forecast the effects of alternative predator harvest scenarios, and estimate the level of hunter offtake that will be sustainable. Additionally, quantifying the sources and timing (neonatal, overwinter) of calf mortality will provide information useful in guiding management actions aimed at increased recruitment. If predation (wolf, black bear, or lion) is the predominant source of calf mortality, liberalized wolf, bear or lion harvests may be effective at reducing mortalities and increasing recruitment. If nutritional carrying capacity is limiting recruitment, however, increasing elk harvest to reduce adult female density or otherwise improving habitat to increase total elk numbers may be effective management strategies.
In addition to the direct application of the findings to the hunting districts in the Bitterroot Valley, this project will provide valuable insights for wildlife managers and biologists across the Rocky Mountain States. While nutritional limitation is typically considered the main driver of elk management, high predator densities and wolf recolonization are relatively new limiting factors for elk in most western states. The role of predation, in the context of other factors limiting elk populations, in affecting elk management is a central issue that wildlife managers now need to understand and incorporate into their decision making processes.
Financial support for this project has been provided by:
Funding was also provided by revenues from the sale of Montana hunting and fishing licenses and matching Federal Aid in Wildlife Restoration grants to Montana Fish, Wildlife & Parks.