Yes, Jeff's description of the bats flying in arcs around tree edges sounds a lot like Silver-haired bat behavior. They are a medium-bodied bat, a little smaller than a Big brown, and don't swoop and dive nearly as much as Big browns. And,. we have them here year round!
http://cascadiaresearch.org/reports/Bats-NWNaturalist-2007.pdf

Greg Falxa
gfalxa at cascadiaresearch.org
Olympia, WA
-------------------
> From: vogelfreund at comcast.net
> Date: July 25, 2011 5:44:32 AM PDT
> To: jeff gibson <gibsondesign at msn.com>
> Cc: tweeters <tweeters at u.washington.edu>
> Subject: Re: [Tweeters] Big Bats in Everett
>
> I hope a bat expert or two shimes in. I have a little paperback titled: The Bats of British Columbia. It pretty much covers the bats of Washington also. One species it could have been is the Silver Haired Bat. I don't know how large your bats were. But it is a medium sized bat and flies straight. I had a close encounter with one many years ago in Bellingham, which got me to buying the book I mentioned.
>
> Best
>
> Phil Hotlen
> Bellingham, WA