Wildlife Conservation Society researchers said they tracked 12 bears living in urban areas around Lake Tahoe, Nev., during a 10-year period and compared them with 10 "wildland" bears living in outlying wild areas. The study found 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 researchers said that obesity led to pregnancies between 4 and 5 years of age, compared with 7 to 8 years for bears in wild areas. Some urban bears even reproduced as early as 2-to-3 years of age around Lake Tahoe.

The researchers also found urban bears tend to die much younger due mostly to collisions with vehicles. All 12 urban bears tracked by the study were dead by age 10 due to vehicle collisions, while six of the wildland bears still survived.

The study is detailed in the journal Human-Wildlife Conflicts.