Wolf (<i>Canis lupus</i>) Winter Density and Territory Size in a Low Biomass Moose (<i>Alces alces</i>) System

Abstract

ABSTRACT. We investigated the winter density and territory size of wolves (Canis lupus) on the Yukon Flats, Alaska, where moose (Alces alces) was the sole ungulate prey, occurring at a low density and representing a biomass of ungulate food lower than previously studied in North America. Using locations (GPS coordinates) from collars deployed on seven wolves, we estimated territory sizes with adaptive kernel and minimum convex polygon methods. We then estimated wolf density from a population area defined by these territory sizes and counts of wolves in five marked packs. From November 2009 to April 2010, we obtained 6263 GPS locations. Pack size ranged from two to 10 wolves, with average size of 5.0 in November 2009 and 4.8 in March 2010. Average winter territory size for the five packs was 1433 km 2 with the 95% adaptive kernel method and 1608 km 2 with the minimum convex polygon method. Density (wolves/1000 km 2 ) was 3.6 in November and 3.4 in March with the 95% adaptive kernel method and 3.4 in November and 3.3 in March with the minimum convex polygon method. Territories were large and estimates produced by the two methods differed by 11%. Densities were low, and the two analysis methods yielded densities that differed from each other by 3% to 6%. Low wolf density corresponded with low biomass of ungulate food, suggesting that moose availability on the Yukon Flats likely limited wolf density.Key words: Alaska; biomass; density; GPS; moose (Alces alces); territory; wolf (Canis lupus) RÉSUMÉ. Nous avons étudié la densité hivernale et la taille du territoire du loup (Canis lupus) aux Yukon Flats, en Alaska, où l'orignal (Alces alces) était la seule proie ongulée. Il s'y trouvait en faible densité et représentait une biomasse de nourriture ongulée inférieure à celle étudiée ailleurs en Amérique du Nord. Grâce aux positions (coordonnées de GPS) prélevées à partir de colliers posés sur sept loups, nous avons estimé la taille des territoires au moyen de la méthode d'estimation adaptative à noyaux et de la méthode du polygone convexe minimal. Ensuite, nous avons estimé la densité du loup à partir d'une zone de population définie par la taille de ces territoires et par les dénombrements de loups de cinq meutes marquées. De novembre 2009 à avril 2010, nous avons obtenu 6 263 positions GPS. La taille des meutes variait de deux à dix loups, pour une taille moyenne de 5,0 loups en novembre 2009 et de 4,8 en mars 2010. La taille moyenne du territoire hivernal de cinq meutes était de 1 433 km 2 dans le cas de la méthode adaptative à noyaux de 95 % et de 1 608 km 2 dans le cas de la méthode du polygone convexe minimal. La densité (loups/1000 km 2 ) était de 3,6 en novembre et de 3,4 en mars avec la méthode adaptative à noyaux de 95 %, puis de 3,4 en novembre et de 3,3 en mars avec la méthode du polygone convexe minimal. Les territoires étaient vastes et les estimations obtenues à l'aide des deux méthodes différaient de 11 %. Les densités étaient faibles, et les deux méthodes d'analyse ont donné des densités qui différaient ...

Wolf kill rates across winter in a low-density moose system in Alaska

“…Predation rate was 12% during the 151‐day period between November 2009 and March 2010. This ratio reflected a November wolf density of 3.7 wolves/1,000 km 2 (Lake et al ), wolf winter kill rate of 0.024 moose/wolf/day, and November moose density of 0.11 moose/km 2 . Moose density was 0.08 moose/km 2 in the 2010 fall survey (Table ), adjusted by 30% moose missed in Interior Alaska (Keech et al ).…”

“…We speculate at least 3 mechanisms contribute to the ability of wolves to maintain kill rates at low moose densities. First, wolves are highly mobile and may have large territories (Ballard et al , Mech et al , Fuller et al , Lake et al ). Such large territories are a response to low prey densities (Peterson , Fuller et al ), and are maintained to ensure an adequate supply of vulnerable prey (Peterson ).…”

“…Minor prey included beaver ( Castor canadensis ) and snowshoe hare ( Lepus americanus ). November 2009 and March 2010 wolf densities ranged from 3.5 to 3.7/1,000 km 2 (Lake et al ). Black bear ( Ursus americanus ) densities were high at ≥155 independent bears/1,000 km 2 in 2010 (Caikoski ).…”

Winter hunting behavior and habitat selection of wolves in a low‐density prey system

“…Aerial estimates during the study period indicated  0.2 moose km -2 in the western and eastern Yukon Flats (Lake et al 2013). Wolf densities in the Yukon Flats were estimated at 3.4-3.6 1000 km -2 (Lake et al 2015). Moose densities are thought to remain at a low-density equilibrium due to high calf mortality from bears, Ursus americanus and U. arctos, and adult mortality from wolves, combined with illegal harvest of adult females (Bertram andVivion 2002, Gasaway et al 1992).…”

Estimating abundance of a cryptic social carnivore using spatially explicit capture–recapture

“…One of the most common means to estimate wolf density is aerial telemetry of marked individuals, wherein wolves are radiocollared from every pack in the survey area, minimum counts of pack sizes are obtained visually through aerial observations, and the total number of wolves is divided by the sum of the pack territory areas (i.e., territory mapping; Peterson et al , Fuller , Hayes ). The aerial radiotelemetry approach has been widely used since the 1970s and remains commonly applied in areas with open terrain (Ballard et al , Hayes et al , Adams et al , Lake et al , Boertje et al ). This method is effective if a sufficient number of wolves are radiocollared and monitored in all adjacent packs in a region (Burch et al ); yet, meeting these requirements is generally expensive, time‐consuming, and difficult to apply over a large area (Boitani , Schmidt et al ).…”