If it pains you to see a wild animal like these black bear cubs in a
dumpster, think how they feel—especially since bears lured to urban
areas by the availability of garbage die at such high rates that not
even getting fat on human detritus and reproducing while still teenagers
(in human years) can compensate for their higher mortality, according
to the first study of overall impact of urban areas on black bears.
It has long been known that garbage attracts bears and causes them to
ditch their natural diet; who wants to scrounge for berries when
there’s half a Big Mac in someone’s uncovered garbage can? But Jon P.
Beckman of the Wildlife Conservation Society
and Carl W. Lacey of the Nevada Department of Wildlife went further.
They followed 22 female black bears—12 in an urban environment and 10 in
wildland habitats—from 1997 to 2006 in the northern Sierra Nevada
Mountains, including around Carson City and Lake Tahoe, to assess the
impact of people and their garbage over the bears’ lifetimes, they
report in the journal Human-Wildlife Conflicts. They find that bears in urban areas weigh more (about 30 percent more
than bears in wild areas, because their natural diet is heavily
supplemented by garbage) and get pregnant at a younger age (on average,
when they are between 4 and 5 years old, rather than 7 to 8 years for
bears in wild areas; some urban bears around Lake Tahoe even reproduced
at the age of 3). Despite these advantages, female bears in urban areas do not leave
more offspring over their lifetime because their lifetime is cut short.
Due to collisions with vehicles, all 12 urban bears in the study were
dead by age 10, while only 4 wildland bears died young. As the
scientists conclude, “bears in urban areas have experienced elevated
levels of mortality that exceed reproductive rates, even though urban
bears are more fecund than wildland bears.” |