Right in Charleston Harbor is the little Crab Bank Heritage Preserve (803/734-3886), where thousands of migratory birds can be seen depending on the season. From October to April you can either kayak there yourself or take a charter with Nature Adventures Outfitters (1900 Iron Swamp Rd., 800/673-0679) out of Awendaw Island.
On James Island southwest of Charleston [1] is Legare Farms (2620 Hanscombe Point Rd., 843/559-0763, www.legarefarms.com [2]), which holds migratory bird walks each Saturday in autumn at 8:30 a.m. ($6 adults, $3 children).
Links:
[1] http://www.moon.com/destinations/charleston-savannah/charleston
[2] http://www.legarefarms.com