Ding Darling National Wildlife Refuge on Sanibel Island is a mecca for birdwatching and bird photography. The preserve protects the bays, bayous, mangroves and shoreline of the northern half of the island. Conditions vary with the tides-- what appears to be a lake with a handful of birds flying overhead will be revealed, a couple of hours later, as a mudflat filled with hundreds of wading birds.
The birds are easily seen from from the 5 mile Wildlife Drive which is open to cars and bikes, or you can ride the tram. The Indigo trail is available for long walks along the dikes and the Calusa trail is a short boardwalk on an ancient Native American shell mound. An observation tower about halfway through the drive gives a bird's eye view. Kayak rental in adjoining Tarpon Bay looks like a fantastic way to visit the refuge if you have time.
Beyond the abundant birdlife, I've seen alligators, raccoons, and a snake slowly swallowing a rat. They say there are manatees in Tarpon Bay, but I haven't seen them.
The visitor center has wildlife exhibits and a bookstore run by the Ding Darling Society. The rangers at the visitor center can recommend the best times and places to see wildlife in the refuge. It's good to plan some flexibility into a visit because of the tidal variation. You can download a map of Ding Darling & Sanibel Island (pdf map) from the FWS. Floridian Nature has information on wading birds and water birds.
I teach economics at Kalamazoo College. My wife is also an economist. We were on sabbatical in Europe for the 2014-15 academic year. (Salamanca, Spain, followed by Oxford, UK.) We were in Uruguay for the 2006-7 academic year.