Portland is known as one of America's most bike-friendly cities. But cyclists have become so alarmed by a growing number of bike thefts that Portland police are creating a task force to catch more of the culprits.

Portland police records show that thieves stole more took more than 2,100 bikes last year worth more than $1 million, reports The Oregonian (http://bit.ly/1DZHb5K ). Records also show an arrest in only about 2 percent of the cases.

This city is swarming with cyclists. Thousands of bike commuters stream in and out of downtown every day. Bike shops dot the neighborhoods. City officials promote cycling by creating bike paths and bike lanes and encouraging motorists to share the road with cyclists.

All of those bikes are tempting targets for thieves, however.

Amid rising complaints about bikes getting purloined, the Portland Police Bureau is establishing a bike theft task force. The bureau planned to release details about the task force Thursday, but postponed the event for a couple weeks.

Police Sgt. Pete Simpson said "we're a bike town," so the effort will be popular with a lot of people.

"The headlines are about mayhem, murder and madness. But most of that does not affect people the way car prowls, bike theft and things like that affect people," Simpson said. "Because it happens to a lot more people."

Though many bicycles are stolen, prosecutors believe there are relatively few thieves. "The 80-20 rule applies — 20 percent of the criminals doing 80 percent of the damage," said Kevin Demer, a Multnomah County deputy district attorney.

Downtown bike shops have posted an array of mug shots showing people they consider chronic suspects. Police may have stopped these suspected thieves on high-end bicycles only to see prosecutors dismiss the theft charge because of insufficient evidence.

"Let's say we know it's your bike because we have your serial number," Demer said. "How do we prove that they know it was stolen?"

Unless the thief admits the crime, the case is sent back to police. The case would fall to property crime detectives whose priorities are largely dictated by dollar values. Bike theft cases are rarely investigated unless the current value of the bike is more than $1,000, the threshold at which the crime becomes a felony, prosecutors say.

Some theft victims have been so frustrated when police were unable to help recover their property they've taken matters into their own hands.

"Is it worth getting stabbed with a rusty screwdriver by a tweaker for a bike? Many people say no," said Bryan Hance, founder of the website StolenBikeRegistry.com. "But some say: 'That was my Dad's bike, it has sentimental value, and I want it back.' "

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Information from: The Oregonian, http://www.oregonlive.com