outside air vent

J.M.

We've got an outside air vent to bring make-up air into the basement room where the boiler is located. The vent goes through one window pane of a basement window. The heating folks who installed it forgot to put anything on the outside to prevent birds from nesting there or rodents from getting in -- which has happened to neighbors. So can we put a baffle on the part that sits in the window (or get someone to do that) or should we just put chicken wire on the actual vent that sits outside the window?
Thanks.