Yes, you will need at least two passes to cover WA birding locales.
1. Discover Pass - $30 annual - good for all WA state parks and state wildlife areas (e.g., W 90 on Samish Flats, Robinson Canyon, Black Canyon, Hardy Canyon)...and yes, now transferrable between two vehicles.

2. Federal pass - I'd advise against the NW Forest Pass. That will only be good for National Forest trailheads, not national parks, BLM lands and NWRs. Get an "interagency pass" formerly known as "Golden Eagle" pass - $80 annual. It covers all the above....and its a steal when you consider one day admission to Mt. Rainier NP is $15. We're hikers and birders, so between Mt. Rainier trips, National Forest trailheads and Nisqually NWR, we save money by purchasing the annual pass. Additionally, know that your $80 fee stays at the location where you purchase it....for example, you can help support Nisqually NWR by purchasing your pass there. If you are 62 or older you can get a LIFETIME Golden Access Pass, same as the Interagency Pass, for a one-time fee of $10, the best deal in town next to me.

Ed Deal
dealgen AT aol.com