How would you guys deal with this? Birds are getting up into the "C" channel along with the bathroom vents. Vents are easy, what would you choose to block the gaps in siding going up behind the "C" channel? Foam will work for a while, but birds tend to peck it out. There's approx. 110 linear feet to seal.

pressure fit wire mesh and a couple dabs of caulk

Yup, hardware cloth. Cut a little big and wedge it up. Caulk edges or corners. Did that to an old deer camp to keep mice out. Works great.

I don't disagree with the others.

I like kwikmesh from Lowes. I don't like cutting anything including this but it works in lots of applications.

Thanks guys, that was pretty much my backup plan.