I don't know much about birding in the Duncan or Vancouver areas. In Greater Victoria there are a number of good birding sites. If you can add a bike to your transportation mix you should have no problem getting to most sites. Here are a few of the easier access ones.
1. Swan Lake - Christmas Hill Nature Sanctuary (one of my favorites) - short walk from a bus route near McKenzie and Highway 17
2. Whitty's Lagoon Regional Park - nice mix of mud flats, intertidal, and forest. A great walk even if on a low-bird day. This is in Metchosin just outside of Victoria. I believe there is a bus, but don't know how frequently it goes.
3. Dallas Road/Ogden Point/Clover Point/Beacon Hill Park - These are all adjacent to each other. If you are in Victoria this is an easy area to get to (simply walk from James Bay, Fairfield or downtown). Not much in the way of songbirds along the water, but often sea ducks, shorebirds etc.
4. Cattle Point and Uplands Park - In Oak Bay, I think bus #11 goes by. Again good area for seabirds (bring a scope if possible) and a nice Garry Oak Meadow walk in the adjacent (across the road) Uplands Park. I believe that the municipality of Oak Bay has a map of the various walking trails.
5. Viaduct Flats (off Interurban). - This is a seasonal marsh area. Lots of good ducks and such. There are buses that go to the collage just down the road, but I don't know if they keep going past Viaduct Flats. It would probably take about 15 minutes to walk from the collage to the flats. Nice viewing tower and trail.
6. Rithets Bog - In the Broadmead area, there is a ~4km trail around the bog. Good mix of bog/marsh/forest. This area is in the intersection of Royal Oak Drive and Hwy 17. If coming from downtown, get off at the overpass and walk though the Broadmead shopping center. Keep going down Chatterton Way. Probably a 15 minute walk from the bus.
You can always get in touch with the Victoria Natural History Society www.vicnhs.bc.ca
they run weekly field trips.