We are currently having this same problem.
Our birds, apparently, are gaining access to our attic through vents
they have pecked at and pushed up to squeeze through. Because we are
remodeling our master bath and have the shower ceiling currently open
to the attic (for electrical and plumbing work), we have had SEVERAL
birds come into our master bath. Two days ago, I came home to find
TWO birds flying around our bathroom. I decided it was time to call
a wild animal control service.
For $169, they came out, extracted the birds (humanely caught and
released outside), inspected where they were coming in, cleaned up
the birds nests, and for $59 more got on our steep room and fixed one
of the problem areas. We chose not to have them replace the vents at
this time, as we are currently looking to replace the current vents
with attic fans. In the meantime, we have sealed the vents from the
inside to prevent continued access.
In my opinion, this was $200 well spent.