The cyclists said they have seen the hawks in previous years but the father bird has been more aggressive this year, regularly attacking those riding their bikes down Tutuilla Creek Road south of Pendleton, the East Oregonian in Pendleton reported Monday.
"He's back and he's much more aggressive," cyclist Mack Temple said. "He came in from behind and whacked me on the top of my helmet -- he's apparently getting bolder."
Lynn Tompkins, executive director of Blue Mountain Wildlife, said the birds are likely Swainson's hawks.
"They are really territorial," she said of Swainson's hawks. "They have a reputation for being aggressive."
Carl Scheeler, wildlife biologist for the Confederated Tribes of the Umatilla Indian Reservation, said the hawks usually incubate for 28-35 days and begin leaving the nest about a month later.
"Typically, the more investment they have in their young, the more likely they are to be aggressive," Scheeler said.