Same problem happened to my 抽油烟机通风管道 couple years ago. First I heated some cooking oil and put some chilly in, turned the 抽油烟机 on, birds flew away immediately. Then we used a metal net to cover the opening on the exterior wall after took off 上面的塑料片
if you can reach with ladder.
You can also buy this kind of guard from Home depot, and ask for professional person to clean the pipe and install it on.