We also plan to birdwatch Cape May, NJ

A bit to the west puts you into the "swamp" area also know as a tidal estuary of the Delaware Bay. The entire Southern Coast of New Jersey is thick with interesting nature areas. Try swinging around Bivalve (yes, that is the name of the town!) There should be plenty of bait shops, etc, which can give you a better steer than I can.

If you want to see Bald Eagles, I can steer you to a site in Pilesgrove Township where you might get lucky.

Not such a great time of year nowadays though. Late Spring might be better. But - that time of year in that area you will run into lots of New Jerseys' state insect - the mosquito!
Mark