Fast-Food Nation Is Taking Its Toll on Black Bears, Too
t's no secret that America's adults are getting fat and sedentary. Its children are becoming couch mini-potatoes. Even its pets are overweight.
Now the fast-food lifestyle is getting to the bears, too.
A study of black bears in the Sierra Nevada has found that those animals that live in and around cities and towns are less active than those in wilderness, spending less of their time foraging for food and fewer days in their winter dens. These and other behavioral changes are making the bears heavier.
The culprit, say the study's authors, Dr. Jon P. Beckmann and Dr. Joel Berger of the Wildlife Conservation Society, is the garbage found at fast-food restaurants and in residential neighborhoods. As many Westerners are all too aware, black bears are forsaking their wild stomping grounds to patrol backyards and parking lots for nutritious trash.
"For a bear, garbage is probably the ultimate food resource," said Dr. Beckmann, who works in the conservation group's field office in Rigby, Idaho. "It's available year-round, it's in the same place week after week, and it's replenished after use."
Nowhere is this more apparent than in the fast-growing Lake Tahoe basin on the California-Nevada border, which Dr. Beckmann and Dr. Berger chose for the study.
The researchers, who also are affiliated with the University of Nevada at Reno, attached radio collars to 59 bears and tracked them from week to week. They found that the animals fell into two camps: country bears, which spent almost all of their time in wild lands, and city bears, which lived in residential areas, often right under people's noses. Some city bears denned beneath homeowners' decks or elsewhere in backyards in towns like Incline Village and Stateline, Nev.
The researchers followed individual bears for 24 hours in the fall to study their foraging habits. In the case of the urban bears, Dr. Beckmann said, that often meant following them from parking lot to parking lot at night while they fished in Dumpsters and garbage cans for their dinner.
A black bear fattening up for the winter is a glutton, eating upward of 20,000 calories a day. In the study, country bears, forced to roam over wild lands searching for pine cones, troves of berry bushes or the occasional prey, spent more than 13 hours a day foraging. City bears, with all that rich garbage for the taking, spent much less time, an average of about 8.5 hours a day.
The city bears, he and Dr. Berger found, had also become nocturnal, foraging at night presumably to avoid being disturbed by people and resting during the day. This is the reverse of normal bear behavior.
Dr. Beckmann said they often found city bears sleeping during the day under a tree or down by a stream under heavy cover. And they occasionally heard reports like one from a woman who opened her bedroom door in the morning to find a "brown lump" in the hallway. It turned out to be a bear that had ransacked her kitchen and was sleeping off the rather substantial meal it had devoured.
Because the garbage supply, unlike the natural food supply, does not diminish in winter, the researchers found that city bears spent an average of 42 fewer days in their winter dens. Some urban bears did not have winter dens at all.
"With Dumpsters, they never have to shut down," Dr. Beckmann said. "They just keep eating."
A normal adult male weighs 220 to 300 pounds, but Dr. Beckmann said that one male of every four they encountered was over 400 pounds, and a few weighed 500 to 600 twice the size of some grizzlies.
For a bear, weight is not unattractive, or unhealthy, as far as anyone knows. Rather, the problem with eating human food is that it brings bears into contact with humans, and the bears invariably lose. That kitchen-ransacking bear, for example, was destroyed. Many other urban bears are killed by motor vehicles. Nevada, Dr. Beckmann said, has only 300 black bears, and is losing about 10 a year to accidents.
The solution, he said, is to require or encourage businesses and homeowners to use bear-proof trash containers. In places where they are used, the bears go elsewhere.
Otherwise, the losses will continue. "It's like a big sink," Dr. Beckmann said. "Mortality rates are much higher than reproductive rates. You can potentially eliminate a black bear population."