Hello Rick-

Sounds like your guest is a little brown bat (Myotis lucifugus). It will probably not stay long- we had one for a day or so last summer. There's useful information in "Living With Wildlife" PDF series provided by the Washington Department of Fish and Wildlife at:

http://wdfw.wa.gov/publications/00605/

which indicates that this behavior is typical of young bats just learning to fly.

There's also more interesting information posted by Bats Northwest:

http://www.batsnorthwest.org/

Bat poop can look a lot like mouse droppings- there were bats roosting under the eaves at our cabin rental in Manzanita- this can be a health hazard, causing a lung disease (histoplasmosis). But bats nearby are more beneficial than not, and help keep the mosquitoes vacuumed up.

This little guy was a Bellevue Master Naturalist's previous "Species of the Year." Some of our group continue to be active with Bats Northwest, and have conducted bat surveys in the Mercer Slough. I have emailed one of them (also a C.O.B. Volunteer Naturalist and a birder), who may have more information for you.

May we ask where you are located?

Hilary Barnes
habarnes at earthlink.net
206-331-6058 cell