Last week I cleared a bird's nest out of my in-laws' dryer vent pipe. It's horizontal for about 17 feet. It's in the floor of the second floor. The hood out on the brick wall decayed from UV rays from the sunlight and broke apart, allowing the robins in. The nest ran pretty much the length of the pipe. I ran the dryer and poked in there dislodging things and it blew out bit by bit. Sorry about the eggs that came out and fell about 12' to their demise. The builder(5 year old townhouse) did a terrible job connecting the hood's bit of pipe to the duct they ran to it. Sleeved together backward(Hood's pipe inside duct) for the airflow direction, and the end of the hood's pipe was dented in enough to catch a lot of stuff. It was pretty much packed. the birds must have loved the warmth. So new it has a better hood, installed correctly.
When I was initially up the ladder investigating, a neighbour told me she'd seen birds going in and out. Oddly, she said they aren't hurting anything. She must've thought I knew about the birds and my purpose there was to attack birds and she objected. I'm guessing that.
Not hurting anything???? True if you don't count burning the house down as hurting something!
There's no problem too big to ignore if you put your mind to it.