Predators Decimate Vancouver Island Marmot Colonies

From field observations it appeared that Vancouver Island marmots frequently were not surviving hibernation, causing their drastic drop in numbers.

Now examining recently deceased marmots located with radio tracking more conclusively shows that mortality during hibernation is uncommon.

Researchers discovered only one occasion when marmots died during hibernation, accounting for 10 percent of 29 deaths documented since 1992.

Instead, 83 percent of marmot mortality results from predation, with 38 percent of identified kills attributed to wolves, 21 percent cougars and 14 percent golden eagles. There is no indication that black bears, bald eagles or other birds of prey hunt Vancouver Island marmots. Researchers encountered four cases of predators repeatedly attacking a colony over a few days, killing 2 or 3 marmots.

Predators mainly target adult marmots, both males and females, with three-quarters of deaths occurring during August and September. The resulting annual survival rate for wild Vancouver Island marmots is 73 percent, below the 80 percent considered necessary to sustain populations.

Marmots have successfully co-existed with wolves and cougars for considerable time, until recently. Evidence suggests that recent changes in wolf and cougar populations in response to fluctuations of their primary prey, black-tailed deer, have triggered increased predation on marmots. Researchers also suspect that landscape alterations from forest harvesting have enhanced Vancouver Island marmot's vulnerability to predators.