Factors affecting gray wolf (Canis lupus) encounter rate with elk (Cervus elaphus) in Yellowstone National Park

Abstract

Despite encounter rates being a key component of kill rate, few studies of large carnivore predation have quantified encounter rates with prey, the factors that influence them, and the relationship between encounter rate and kill rate. The study’s primary motivation was to determine the relationship between prey density and encounter rate in understanding the mechanism behind the functional response. Elk (Cervus elaphus Linnaeus, 1758) population decline and variable weather in northern Yellowstone National Park provided an opportunity to examine how these factors influenced wolf (Canis lupus Linnaeus, 1758) encounter rates with elk. We explored how factors associated with wolf kill rate and encounter rate in other systems (season, elk density, elk group density, average elk group size, snow depth, wolf pack size, and territory size) influenced wolf–elk encounter rate in Yellowstone National Park. Elk density was the only factor significantly correlated with wolf–elk encounter rate, and we found a nonlinear density-dependent relationship that may be a mechanism for a functional response in this system. Encounter rate was correlated with number of elk killed during early winter but not late winter. Weak effects of snow depth and elk group size on encounter rate suggest that these factors influence kill rate via hunting success because kill rate is the product of hunting success and encounter rate.

Predator foraging response to a resurgent dangerous prey

“…We used these data to calculate the annual ratio of bison and elk attacks ( a bison / a elk ; ‘relative attack frequency’). Within the park winter range, wolf encounter rate with elk covaried with elk abundance (Martin ).…”

Population responses of common ravens to reintroduced gray wolves

“…Not every carcass fed on my wolves is detected (Smith et al, ), and we may have therefore underestimated the total biomass that wolves provision to scavengers every March. However, variation in detection probability likely had minimal influence on our results because we standardized our annual estimates, using a method to estimate rates of biomass acquisition only on days when ground packs were actually observed (Martin et al, ). Furthermore, our methods were consistent throughout the study, and any underestimation of biomass would therefore be unlikely to impact the reported trends.…”

“…We then divided this number by the average number of survey days where ground packs were located either visually by air or ground crews or, for the aircrew, using radio telemetry. Estimating biomass acquisition rate using this method reduces the effect of interannual variation in monitoring success (i.e., detecting wolves; Martin et al, ). Finally, to estimate the total biomass acquired by the entire Northern Range wolf population, we multiplied this annual estimate of daily biomass acquisition rate by the total number of wolves on the Northern Range.…”

How climate impacts the composition of wolf‐killed elk in northern Yellowstone National Park

“…The dataset for this analysis runs through March 2017, although we excluded data from the winters of 2013–2014 and 2014–2015 because of missing productivity data (see Section 2.2 below). Each year during the study, we used aerial‐ and ground‐based observations to intensively monitor two or three wolf packs for 1 month in both early winter (approximately 15 November–14 December) and late winter (approximately 1–30 March) on the Northern Range of YNP ( n = 17 total packs over 40 unique study periods; see Martin et al, 2018 for further details). Except for one pack during one 30‐day period (Junction Butte during early winter 2012), we maintained at least one VHF collar on a wolf in each pack, thus allowing us to find each pack on a nearly daily basis using radio telemetry.…”