Abstract
Large migratory catibou {Rangifer tarandus) herds in the Arctic tend to be cyclic, and population trends are mainly driven by changes in forage or weather events, not by predation. We estimated daily kill rate by wolves on adult caribou in winter, then constructed a time and space dependent model to estimate annual wolf (Canis lupus) predation rate (P annual) on adult Porcupine caribou. Our model adjusts predation seasonally depending on caribou distribution: Pannual = SIGMAdaily* W *Ap(2)*Dp. In our model we assumed that wolves killed adult caribou at a constant rate (Kdaily, 0.08 caribou wolf1 day1) based on our studies and elsewhere; that wolf density (W) doubled to 6 wolves 1000 km2-1 on all seasonal ranges; and that the average area occupied by the Porcupine caribou herd (PCH) in eight seasonal life cycle periods (Dp ) was two times gteater than the area described by the outer boundaries of telemetry data (Ap /1000 km2). Results from our model projected that wolves kill about 7600 adult caribou each year, regardless of herd size. The model estimated that wolves removed 5.8 to 7.4% of adult caribou as the herd declined in the 1990s. Our predation rate model supports the hypothesis of Bergerud that spacing away by caribou is an effective anti-predatory strategy that greatly reduces wolf predation on adult caribou in the spring and summer.
Highlights
Migratorybarren - groundcaribou {Rangifer tarandus) herds showwidepopulation fluctuations t h a t have been explained by changes i n forage, climate, predationand harvest
The lowest k i l l rate was for wolves i n the Rat River II pack (Table 1) which scavenged frommanyhunterkills in the area
We estimated the wolfkill rate was 0.08 ± 0.03 caribou per day per wolf; or 7.5 ± 2.7 k g of caribou killed per w o l f per day
Summary
Migratorybarren - groundcaribou {Rangifer tarandus) herds showwidepopulation fluctuations t h a t have been explained by changes i n forage, climate, predationand harvest (as reviewedinKlein , 1 9 9 1 ). Weestimatedannual predation rate as the propor - tion of adult Porcupine caribou killed by wolves. To determine the rate of w o l f predation on the Porcupine herd we needed a model that was based on reasonable ecological assumptions about wolves and caribou. N o t all wolves have caribou available to them each year, and the number musr vary w i t h the area caribou occupy during different phases oftheirannuallife cycle (e.g., springmigra - tion, calving, winter). This means that we cannot estimatepredation rate bysimplyapplyinga fixed k i l l daily rate to the entire wolf population.
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