We have Barn Swallows nesting in what sounds like a very similar spot every year. We remove the nest every fall and the birds seem to return and rebuild anyway. We remove the nests for two reasons:
1) Hopefully it helps control the nearly annual major infestation of bird mites. It is hard to imagine how many bird mites can be in a single nest without seeing these parades of nearly microscopic bugs. We're talking thousands.
2) The nest is built on a porch light and I think it is a fire hazard to use the light with the nest on it. Obviously we don't use the light when the birds are there.

Hope this helps,

Jim Elder
Seattle, WA (Queen Anne neighborhood)

----------
From: tweeters at u.washington.edu[SMTP:tweeters at u.washington.edu]
Sent: Monday, February 15, 1999 12:07 AM
To: Northwest birding email
Subject: TWEETERS digest 1671

Date: 14 Feb 99 23:18:17 PST
From: Ed Newbold <newboldwildlife at netscape.net>
To: tweeters at u.washington.edu
Subject: barn swallow nest

But here's what I'm really writing to find out. Last year we were landlo=
rds
to a Barn Swallow family above our front steps and they fledged three you=
ng. =

Since they were a lot of fun and I've heard they are declining nationally=
, I
am understandably eager to have them back. They picked a really good saf=
e
place where we can help them fight off cats and crows and it would probab=
ly be
good if they stayed exactly in that same place. So my question is: Shou=
ld I
knock the old nest out or leave it there?