Evaluating Bottom-Up and Top-Down Effects on Elk Survival and Recruitment: A Case Study in the Bitterroot Valley

Scientific Disciplines
Biological Sciences - Terrestrial
Montana Fish Wildlife Parks
Canis lupus
Cervus elaphus
causespecific mortality
university montana missoula
Bitterroot Valley
Volume 18, No. 1-4

Evaluating bottom-up and top-down effects on 
Elk survival and recruitment: a case study in the 
Bitterroot valley
Sonja Christensen*, Wildlife Biology Program, University of Montana, Missoula, MT, 59812
Kelly Proffitt, Montana Fish, Wildlife, and Parks, Bozeman, MT, 59718
Mark Hebblewhite, Wildlife Biology Program, University of Montana, Missoula, MT, 59812
Ben Jimenez, Montana Fish, Wildlife, and Parks, Missoula, MT, 59804
Craig Jourdonnais, Montana Fish, Wildlife, and Parks, Missoula, MT, 59804
Mike Thompson, Montana Fish, Wildlife, and Parks, Missoula, MT, 59804
Understanding the contribution of recruitment rates to overall growth rate in ungulate 
populations is a fundamental challenge in wildlife management. Ungulate populations with 
low recruitment rates may result in population level declines over time. In the southern 
Bitterroot Valley of western Montana, the decline of elk (Cervus elaphus) populations and calf 
recruitment occurred concurrently with wolf (Canis lupus) recovery. However, a multitude of 
abiotic, bottom-up and top-down factors likely affect recruitment rates and the relative affects 
of these factors on elk calf survival rate likely vary temporally throughout the first year.  We 
studied cause-specific mortality of elk calves to understand the role of competing mortality 
risk on calf recruitment in the East Fork and West Fork of the Bitterroot Valley, Montana. A 
total of 66 neonatal elk calves were captured in spring 2011 and an additional 31 6-month 

olds in late November 2011. We will analyze survival using a Weibull parametric survival 
model, and cause-specific mortality using a competing risks framework. Preliminary analyses 
suggest the potential for competing risks between black bears, mountain lions, and wolves.  
As the study progresses into the second year, we will evaluate the role of summer range 
nutritional resources on maternal condition, lactation performance, and calf birth weights and 
survival. Our study will fill a gap regarding the role of summer vs winter mortality in elk and 
the role of nutrition in first year survival. The study will complement previous studies on elk 
population dynamics and inform elk population management following carnivore recovery.