Development and Application of a Ratio Estimator to Estimate Wolf Kill Rates and Variance in a Multiple-Prey System

Estimating number of prey killed by carnivores such as wolves (Canis lupus) per unit time, or kill rate, is important for the conservation and management of carnivores and their prey. We reviewed published methods to estimate wolf kill rates and found them inconsistent and lacking a basis in statist...

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Bibliographic Details
Published in:Wildlife Society bulletin 2003-12, Vol.31 (4), p.933-946
Main Authors: Hebblewhite, Mark, Paquet, Paul C., Pletscher, Daniel H., Lessard, Robert B., Callaghan, Carolyn J.
Format: Article
Language:English
Subjects:
Canis lupus
Carnivore Research and Management
Cervus elaphus
Elks
Estimation methods
Estimators
Musical intervals
National parks
Predation
Statistical variance
Wildlife ecology
Wildlife management
Wolves
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Summary:Estimating number of prey killed by carnivores such as wolves (Canis lupus) per unit time, or kill rate, is important for the conservation and management of carnivores and their prey. We reviewed published methods to estimate wolf kill rates and found them inconsistent and lacking a basis in statistical sampling theory. We developed a general statistical estimator for kill rate and variance using ratio-variable sampling theory. We illustrate our ratio estimator by estimating wolf kill rates in a multiple-prey system in Banff National Park, Alberta, for winters from 1986 to 2000. We used snow tracking and radiotelemetry to locate 429 kills during 195 sampling intervals covering 1,294 days. Mean kill rate by wolf packs (expressed as the number of kills/day/pack, k/d/p) was 0.33 k/d/p, most of which, 0.23 k/d/p, were elk (Cervus elaphus), the most abundant ungulate. Kill-rate estimates were variable despite intensive sampling effort. The mean kill rate of 0.33 k/d/p had a pooled 95% confidence interval of 0.29 to 0.37. An intensive sampling effort of ≥6-8 individual sampling intervals covering approximately 25% of the winter was required to minimize sampling variation. We compared our method to 3 other published methods for estimating kill rates and examined the bias and precision of kill-rate methods using simulations. Our ratio estimator approach was the least biased and most precise when compared to other approaches. Ratio estimators provide a standardized method to estimate kill rates in other predator-prey systems and will facilitate comparison across studies and examination of patterns of kill-rate variation.
ISSN:0091-7648
1938-5463