DENVER (AP) _ A 10-month-old boy watching polar bears at the zoo was hit in the head by a stray bullet from a nearby gang shootout, police said.

Ignacio Fabian Pardo was hit in the forehead Sunday, but the bullet did not penetrate his skull, apparently because it ricocheted off cage bars at the Denver Zoo, police Sgt. Robbi McKay said.

He was listed in serious condition at Denver General Hospital, but the wound was not considered life-threatening.

''It's very unusual,'' McKay said. ''I think (the bullet) had lost a lot of its velocity and that's why it wasn't more serious.''

Investigators believe the shot was fired during a reported exchange of 19 shots between gangs about two blocks away in another part of City Park, where the zoo is located.

Three people were arrested about three hours after the shooting. Their names and ages were not released.