Beavers (Castor canadensis) can be a significant prey item for wolves (Canis lupus) in boreal ecosystems due to their abundance and vulnerability on land. How wolves hunt beavers in these systems is largely unknown, however, because observing predation is challenging. We inferred how wolves hunt beavers by identifying kill sites using clusters of locations from GPS-collared wolves in Voyageurs National Park, Minnesota. We identified 22 sites where wolves from 4 different packs killed beavers. We classified these kill sites into 8 categories based on the beaver-habitat type near which each kill occurred. Seasonal variation existed in types of kill sites as 7 of 12 (58%) kills in the spring occurred at sites below dams and on shorelines, and 8 of 10 (80%) kills in the fall occurred near feeding trails and canals. From these kill sites we deduced that the typical hunting strategy has 3 components: 1) waiting near areas of high beaver use (e.g., feeding trails) until a beaver comes near shore or ashore, 2) using vegetation, the dam, or other habitat features for concealment, and 3) immediately attacking the beaver, or ambushing the beaver by cutting off access to water. By identifying kill sites and inferring hunting behavior we have provided the most complete description available of how and where wolves hunt and kill beavers.

Gray wolves are a premier example of how predators can transform ecosystems through trophic cascades. However, whether wolves change ecosystems as drastically as previously suggested has been increasingly questioned. We demonstrate how wolves alter wetland creation and recolonization by killing dispersing beavers. Beavers are ecosystem engineers that generate most wetland creation throughout boreal ecosystems. By studying beaver pond creation and recolonization patterns coupled with wolf predation on beavers, we determined that 84% of newly created and recolonized beaver ponds remained occupied until the fall, whereas 0% of newly created and recolonized ponds remained active after a wolf killed the dispersing beaver that colonized that pond. By affecting where and when beavers engineer ecosystems, wolves alter all of the ecological processes (e.g., water storage, nutrient cycling, and forest succession) that occur due to beaver-created impoundments. Our study demonstrates how predators have an outsized effect on ecosystems when they kill ecosystem engineers.

Wolf (Canis lupus L., 1758) diet is commonly estimated via scat analysis. Several researchers have concluded that scat collection method can bias diet estimates, but none of these studies properly accounted for interpack, age class, and temporal variability, all of which could bias diet estimates. We tested whether different scat collection methods yielded different wolf diet estimates after accounting for these other potential biases. We collected scats (n = 2406) monthly from four packs via three scat collection methods (at home sites, at clusters of GPS locations, and opportunistically) in and adjacent to Voyageurs National Park, Minnesota, USA, during April–October 2015. Diet estimates were not affected by scat collection method but did vary temporally, among packs, and by age class. To more accurately estimate wolf population diets, researchers should collect 10–20 adult scats/pack per month from home sites and (or) opportunistically from packs that are representative of the population of interest. Doing so will minimize the potential biases associated with temporal, interpack, and age-class variability.

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1.Predator-prey relationships can have wide-ranging ecological and landscapelevel effects. Knowledge of these relationships is therefore crucial to understanding how these systems function and how changes in predator-prey communities affect these systems. Grey wolves Canis lupus can be significant predators of beavers Castor spp., and conversely, beavers can be important prey for wolves, but wolf-beaver dynamics in North America, Europe, and Asia are poorly understood. 2. Our objectives were to synthesise current knowledge regarding wolf-beaver interactions and to identify knowledge gaps that should be targeted for study to increase our understanding of wolf-beaver dynamics. 3. During the ice-free season, beavers are vulnerable to predation and can be the primary or secondary prey of wolves, but the factors that affect beaver consumption by wolves are complex and are likely dependent on biological and environmental factors. 4. High beaver abundance can increase wolf pup survival, and beavers may subsidise wolves during periods of reduced ungulate abundance. Thus, many researchers have suggested that beaver densities adversely affect ungulate populations through apparent competition, though this remains largely untested. 5. The effects of wolf predation on beaver population dynamics are poorly understood, as most assessments are lacking in quantitative rigor and are instead based on indirect methods (e.g. scat analysis), anecdotal evidence, or speculation. To understand the effect of predation on beaver populations fully, better estimates (e.g. from documented predation events) of wolf predation on beavers are necessary. 6. Given the complexities of wolf-ungulate-beaver systems, fully understanding wolf-beaver dynamics will be challenging and is likely to require long-term, intensive research of wolf, ungulate, and beaver population parameters.Understanding this dynamic has implications, not only for the conservation and management of wolves and beavers, but also for ungulate populations, which are affected by the numerical and functional responses of wolves in these same systems. Mammal Review ISSN 0305-1838 bs_bs_banner Mammal Review 48 (2018) 123-138

Comprehensive knowledge of ambush behavior requires an understanding of where a predator expects prey to be, which is generally unknowable because ambush predators often hunt mobile prey that exhibit complex, irregular, or inconspicuous movements. Wolves (Canis lupus) are primarily cursorial predators, but they use ambush strategies to hunt beavers (Castor canadensis). Terrestrial beaver activity is predictable because beavers use well-defined, conspicuous habitat features repeatedly. Thus, studying where wolves wait-in-ambush for beavers provides a unique opportunity to understand how predators choose ambush locations in relation to prey activity. We searched 11 817 clusters of GPS locations from wolves in the Greater Voyageurs Ecosystem, International Falls, MN, and documented 748 ambushing sites and 214 instances where wolves killed beavers. Wolves chose ambush locations: 1) with olfactory concealment to avoid detection from the highly developed olfactory senses of beavers and 2) close (generally <5 m) to beaver habitat features to take advantage of beavers’ inability to visually detect motionless predators. Our work describes in detail the ambush strategies wolves use to hunt beavers and continues to overturn the traditional notion that wolves rely solely on cursorial hunting strategies. We also demonstrate that ambush predators can anticipate the movements and behavior of their prey due to a fundamental understanding of their prey’s sensory abilities. Wolves, therefore, and likely ambush predators in general, appear capable of simultaneously accounting for abiotic and biotic factors when choosing ambush locations, ultimately allowing them to counter and capitalize on the sensory abilities of their prey.

Wolves (Canis lupus) can be primary predators of beavers (Castor canadensis), but little is known about wolf‐beaver dynamics. We identified kills from 1 wolf (V009) of the Ash River Pack in Voyageurs National Park from 1 April to 5 November 2015 to provide direct estimates of wolf pack kill and predation rates of beavers. We documented 12 beaver kills by V009 during the 2015 ice‐free season and estimated V009 killed 22 beavers during this period. Based on the number of beavers killed by V009, we estimated the Ash River Pack removed 80–88 beavers (kill rate of 0.085–0.095 beavers/wolf/day), which was 38–42% of the beaver population in their home range during the ice‐free season. Even with this substantial level of predation in 2015, the beaver population in the Ash River Pack home range increased by an estimated 43% in 2016, which suggested dispersal from more densely populated adjacent areas likely compensated for the effects of wolf predation. We have presented the first direct estimate of wolf kill and predation rates on beavers, but more research is necessary to understand how wolf predation affects beaver populations under a variety of conditions. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.