I investigated the carcass—an old bull surrounded by crimson wolf tracks on snow, its flesh still warm beneath my hands. Already the wolves had removed most of its hindquarter meat and some organs. While Dave photographed it I looked up, my senses sharpened by the coppery scent of blood and this primal encounter with the ecology of fear. A fresh carcass soon draws cougars and bears; I lingered only sufficiently to record location coordinates.
The next morning a young grizzly fed on the carcass. I watched it patiently for an hour as it removed much of the remaining meat, made a vain attempt to haul the still heavy carcass up the bench, and then lumbered away to sleep off its meal. All the while a Steller's jay perched on a downed log just to the side of the carcass. It repeatedly tried to scavenge meat, each attempt met by a growl and swat from the grizzly. Later that day I observed a coyote trotting through the area, balancing a purloined elk leg in its mouth. Bears emerge from their dens in April, ravenously hungry. One of their survival strategies involves searching out wolf kills. In this park, as in Yellowstone National Park, many wolf kills end up usurped by grizzlies. Carcasses such as this one show how apex carnivore predation can support a wealth of species, from grizzlies to jays to coyotes.
Six months later, in mid-November, I worked in Waterton Lakes National Park. The wind blasted across the Alberta prairie, nearly knocking over my tripod and spotting scope. I steadied them with gloved hands and tucked my chin deeper into the collar of my down parka. It felt more like mid-January in this extreme landscape, where most years the only month I didn't experience snow at my field sites was July. I was out there using yet another method to determine whether elk fear wolves. Conservation biologist Joel Berger, who has done global research on the fear of predation, believes this phenomenon underscores more fundamental questions—the meaning of fear itself and how it can affect ecosystems.
My teenage daughter Bianca had joined me in the field. We were watching a herd of approximately four hundred elk cows, which stood on a high benchland on the southeastern border of the park. Most had their heads up, scanning the landscape rather than eating. They skittishly grazed on tawny dried remnants of prairie grasses that poked up through the thin snow, taking quick bites, looking up for some long moments before stealing another mouthful of food.
"What's up with the elk?" asked Bianca.
"You'd think there were wolves nearby," I said.
"You think?" she asked.
Soon the wolves would oblige us with an answer.
The ecology of fear has deep roots. Staying alive during the early Pleistocene epoch involved escaping large creatures with sharp teeth and claws. This meant that prey species evolved behavior driven by survival. Vigilance—time spent head up, looking for threats—is essential for survival in systems with top predators, but it comes at the expense of time spent eating. For the past two years I had been doing focal animal observations on elk. This involved watching one animal at a time, recording how long it spent with its head down feeding versus head up, scanning for predators. I had categorized my study sites as areas of high, medium, and low wolf presence. I wanted to know whether fear varied on the basis of wolf density and, from that, to learn how many wolves would be enough to trigger changes in herbivory patterns—a trophic cascade. Would one pack passing through an area occasionally, but not denning there, have the same effect as two very large packs that had produced multiple litters of pups in one year? How about one pack that kept hanging on despite losing half of its members annually as a result of human-caused mortality in an area where it was legal to shoot wolves outside the park? The elk I observed on that blustery November afternoon in my medium wolf density area were far more skittish than usual.