Historically, the people of Boulder have been hard on bears.

It began, I suppose, with the North American giant short-faced bear, Arctodus simus, an enormous brute that lived here from about 3 million years ago to 11,000 years ago.

Males weighed up to 2,500 pounds and towered over 11 feet when they reared on their hind legs; they left claw marks 15 feet above the floor in Riverbluff Cave, a paleontological site in Missouri.

These were carnivores, with large, cutting teeth and very powerful jaws. During their last few thousand years, they would have preyed on buffalo, camels, deer, horses, giant ground sloths and two species of bison.

Short-faced bears would have overlapped with, perhaps even competed with, the first Native Americans for at least 2,000 years. Remember that in May of 2009, Patrick Mahaffy found a cache of 83 cutting tools used by Clovis hunters working near Gregory Canyon 13,000 years ago.

Short-faced bears went extinct 11,000 years ago as part of the megafaunal extinction that took the majority of the large animals, such as ancient buffalo and mammoths. Causes of the extinction are the subject of lingering debate, but most people acknowledge that both climate change and Clovis hunters probably contributed to the extinction of the large mammals.

Before trappers and hunters arrived in Colorado, grizzly bears, Ursus arctos, were common in the western two-thirds of the state. While not as large as the extinct short-faced bears, they are huge, fast and powerful. Males usually weigh 600 to 900 pounds, though reliable accounts report males weighing about 1,500 pounds. A large male standing on its back legs is 10 feet tall.

Grizzly bears are omnivores, truly opportunistic hunters and foragers. They eat berries, fruit, conifer seeds, fish, animals ranging in size from ground squirrels to moose, and carrion.

The hunters and trappers that first came to Colorado prized grizzly bears for their fur and meat. Ranchers feared what they might do to livestock and to family members who inadvertently ventured too close to cubs while the adult female was nearby. So the bears were hunted and trapped relentlessly and their numbers declined sharply after 1900. They were thought to be extinct by about 1950.

But then a grizzly attacked a hunter in 1979, surprising everyone. There are still accounts of possible grizzly sightings in Colorado, though skepticism is rising as decades pass.

Black bears, Ursus americanus, were here with short-faced bears when the Clovis people arrived, approximately 13,000 years ago (the date is disputed). They watched the short-faced bear go extinct with most of the large mammals, and watched grizzly be exterminated in the southern Rocky Mountains.

Black bears are quite variable in color. The photo shows a pair of sibs, one black, one cinnamon, belonging to a black female. In other areas, black bears can be brown, and the "ghost bears" along the Pacific Coast of Canada are white, but not albino.

A large male black bear can weigh almost 600 pounds and females can grow to about 450 pounds. But they are powerful for their size and can bend and peel car doors to get to coolers inside. They are clever and can open screw-top containers.

Our Open Space and Mountain Parks are home to black bears, and I have always enjoyed knowing that next to town, bears and lions still live in natural environments.

I have lived close to the mountain park for almost 40 years and I have witnessed a sad trend, particularly in the last decade. More and more, black bears are coming into town and that doesn't always end well. They come to get an easy meal from the garbage cans in the alleys and behind houses.

Speaking only for myself, and my personal experiences, and my neighborhood, student rental houses have proliferated in the last decade, and the students, unaccustomed to taking care of a yard or putting out garbage, are the biggest problem.

Both last year and this year, students seemed incapable of securing their garbage cans and the bears found the cans that were never secured. We warned students, instructed them, even bought them bungee cords for their garbage cans. But the students could not be bothered taking care of garbage, so night after night, the bears were back.

Authorities in Boulder have put down four bears this year. When a bear is trapped repeatedly for visiting garbage cans and hanging around, it is declared a nuisance and put down. That may appear to solve the problem, but the problem, it seems to me, is irresponsible and slovenly people who cannot be bothered to act responsibly.

We need to solve that problem.

The youngsters in the photo have been relocated to Grand Lake; their mother was terminated.