PORTLAND, Ore. (AP) - Bicyclists and joggers whizzing by in synthetic garb and high-tech gear may have been startled by the fallen alders and English oaks in a downtown Portland park, but there was a perfectly natural explanation - beavers at work.

Beavers have chomped into half a dozen trees along the Vera Katz Eastside Esplanade, a riverfront walkway named for the city's former mayor.

At first city workers thought it was the work of vandals. Bite marks revealed beavers as the real culprits. Hoping to keep the rodents out, city workers have put up 4-foot-high wrappings of chicken wire around the trees.

How'd the beavers get to downtown Portland?

Well, this is the Beaver State, after all, and the rodent has managed to survive in an urban setting.

The city beavers find niches in an upstream natural area, said parks ecologist Mark Wilson, and they go about their nocturnal rounds so they are seldom seen, by humans.

But they think little of swimming a couple of miles to eat - trees are sustenance and a means to sharpen and shorten their teeth, which grow constantly through their lives.

Since this is the time of year that 2-year-old beavers leave the family lodge to set up new digs, the downed trees could be evidence of a population on the move.

"They've adapted quite nicely to the urban setting," Wilson said. "They've learned how to make a living in the city."

(Copyright 2007 by The Associated Press. All Rights Reserved.)