WASHINGTON — When the sun goes down, it’s no more Mr. Nice Owl, says a Montgomery Parks spokeswoman.

Montgomery Parks is warning people about a barred owl that has been attacking runners on the Capital Crescent Trail in Bethesda.

A sign warns trail users about the bad-tempered bird: “CAUTION! An aggressive owl lives here,” it reads.

Three people have recently been attacked. The owl swoops down and strikes runners from behind.

“These owls are typically active at night; they’re territorial,” says Melissa Chotiner, of Montgomery Parks. Each of the incidents has happened after sunset.

“We want users to know the safety policy is for users to use the trail only between sunrise and sunset,” she says.

She suggests making noise as the owl approaches. Tucking ponytails inside hats may also prevent confusion with other animals, she says.