The first ever direct estimate of wolf kill rates and predation rates of beavers was researched during 2015 in Minnesota's Voyageurs National Park............Two previous studies had relied on scat analysis, an imperfect measure of what an animal consumes because it does not determine direct kills versu scavenging.........U. of Minnesota biologist Thomas Gable and National Park Service biologist Steve Windels monitored one specific Wolf from April 1-November 5, 2015 and determined that it killed 22 Beaver.............Using this statistic, their extrapolated projection determined that Great Lake Wolf packs kill roughly 40% of the Beaver in their territory, a % that would seem to suggest that Wolves drastically dampen Beaver populations annually........"Note that stable or growing beaver populations typically decrease when total annual mortality rates exceed 25–33% (Henry and Bookhout 1969; Payne 1984, 1989; Novak 1987; Potvin et al. 1992)"................."However, further investigation by Gable and Windels showed that beavers from adjacent territories so replaced the Beaver taken by the Wolves, that the Beaver population actually increased by 43% the following year of 2016"............"These results suggest that wolf predation on dense beaver populations has minimal impact".............. "For example, the 43% increase in beaver density in the study region from 2015 to 2016 was consistent with the 27% increase in beaver lodge density in Voyageurs Park as a whole during the same period (S. K. Windels, unpublished data)"

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https://www.researchgate.net/publication/321091629_Kill_rates_and_predation_rates_of_wolves_on_beavers

Kill Rates and Predation Rates of Wolves on Beavers 

THOMAS D. GABLE , 1 Voyageurs National Park, 360 Highway 11 E, International Falls, MN 56649, USA STEVE K. WINDELS, Voyageurs National Park, 360 Highway 11 E, International Falls, MN 56649, USA 

ABSTRACT 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.