The trailheads are full again. Across the mountain West and the Northeast, summer fills the backcountry with people, and it is prime season for crossing paths with a bear. Mostly, neither side is looking for the other. Two separate calendars, human recreation and bear biology, crowd into the same summer weeks, and a warming climate is changing when and why they meet.
For a bear, summer is the run-up to hyperphagia, the late-season binge that lays down the fat it needs to survive winter. The hunger comes on a schedule. A bear’s appetite builds through the summer and peaks in the fall, when a big brown bear may eat almost around the clock and take in tens of thousands of calories a day. People arrive on the trails as that hunger climbs.
More People, Longer Bear Years
Two things bring them together more often. One is us. More people live near and move through bear country than a generation ago, and in wealthy countries the rare attack usually comes during something ordinary, a hike, a campsite, a walk with the dog.
The other is the bears’ lengthening year. In one Alberta population, it was estimated that a four-degree-Celsius rise in spring temperature moved den emergence about ten days earlier. Warmth and access to human food can shorten hibernation too, and where that happens the active season runs longer, into more of the months people are outside.
When the Food Fails in Summer
A longer, busier overlap would still be quiet if the bears were well fed, and most years they are. The trouble comes in the years the wild food falls short. Warming can nudge spring growth earlier, leaving the berry and nut crops bears rely on exposed when a hard freeze follows, and in northwestern Nevada the years with a late final freeze brought more conflict with people and more bears killed by managers.
Drought does similar work. In New York, the serious conflicts cluster from July through September and run higher in dry years. One of the clearest cases is British Columbia’s salmon coast. Halve the salmon run, the researchers found, and bears killed in conflicts with people rise by about a fifth. A bear short of wild food in August starts searching, and the search can lead toward town.
What the Numbers Can and Cannot Say
None of this makes a warming climate the whole story. In much of bear country, more people and recovering bear populations simply put the two on the same ground. Vermont’s black bears now run well above the state’s management target, and the crowds in the backcountry keep growing. The bears at the edge of town are not necessarily the hungry ones. When researchers in Scandinavia studied brown bears around settlements, they found little sign the animals came in for better food. Much of what looks like desperation is closer to opportunity and overlap.
An encounter almost never becomes an attack. People and bears cross paths many thousands of times each summer, and the great majority of meetings end with the bear wandering off. Brown bears, more dangerous than the black bears most hikers meet, were behind about 664 attacks on people worldwide from 2000 to 2015, a few dozen a year across three continents, and about half the people hurt were out for recreation. The risk to any one hiker on any one day is very small. The attacks that do happen turn on particular bad luck, a surprise meeting at close range or a female defending cubs. Carrying bear spray in grizzly country and making noise on the trail shrink even that.
The makings of a bad bear year can often be seen coming, in a damaging spring freeze, a failed berry crop or a weak salmon run. None of that is a reason to stay home. Just keep your wits about you in late summer, when the bears are hungriest and the trails are busiest.
