(CBS) — Chicago’s hosting an extremely rare visitor which is good for bird watchers but tough on other birds, reports WBBM’s John Cody.

Wildlife biologist Chris Anchor with Cook County Forest Preserve District says the same conditions that brought snowy owls to Chicago have also brought Chicago the biggest falcon in the world.

The Gyrfalcon has a wing span up to 4 and 1/2 feet and weighs three or four pounds. Anchor says they can kill other birds as large as ducks and geese.

He says the Gyrfalcon, spotted at Navy Pier and also in Barrington northwest of Chicago, has a maximum air speed of 120 miles an hour.

Anchor says this is only the fourth one he’s seen in his 30-year career as a wildlife biologist.