Life is tough for a city bear. Nutritious food is scarce, so dinner often comes from the dumpster. Speeding cars lurk around every corner. Mama bears aren’t much older than their cubs. They live fast and die young.
According to a study by WCS-North America, black bears that live around urban areas weigh more, become pregnant at a younger age, and are more likely to suffer violent deaths by motor vehicles. The researchers, who published their study in the Fall 2008 issue of the journal Human-Wildlife Conflicts, tracked 12 bears over a decade in urban areas around Lake Tahoe, Nevada.
Comparing their study subjects to ten bears that lived in outlying wild areas, the authors found striking contrasts. Bears in urbanized areas weighed an average of 30 percent more than bears in wild areas due to a diet heavily supplemented by garbage. The authors believe that the heavier bears give birth at an earlier age—between four and five years old, on average, as compared to seven to eight years for bears in wild areas. Some of the urban bears even reproduced as early as two to three years of age.
The researchers also found that urban bears tend to die at a much younger age, mostly from collisions with vehicles. All 12 of the urban bears they studied had been killed by vehicles by age ten, while six of the wildland bears survived beyond this period. Bear cubs in urban areas also had dramatically higher mortality rates due mainly to vehicle.
“Urban areas are becoming the ultimate bear traps,” said WCS researcher Jon Beckmann, the study’s lead author. “Because of an abundant food source—namely garbage—bears are being drawn from backcountry areas into urbanized landscapes where they meet their demise.”
As a result, bears are failing to re-colonize outlying wild areas following this shift to urban centers. The authors believe that without these urban “sinks,” populations of black bears in Nevada could increase. Right now, populations in Nevada remain steady because bears are immigrating from neighboring California.
WCS is studying the effects of urbanization and sprawl on a variety of wildlife and habitats in North America. Conservation efforts include working with local authorities to increase the use of bear-proof garbage containers and education outreach to reduce conflict in communities where humans and bears share their turf.
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