The exhibition hall at the Black-Faced Spoonbill Reserve on Tainan's west coast explains the ecology of the Tseng Wen River (曾文溪) and the creatures that live there, which includes the extremely rare black-faced spoonbill. The reserve, open 24 hours, is a small section of wetlands that's dedicated to protecting the water bird, which spends the summer (May to September) in Korea and northern China, and migrates to Tainan for the winter.
If you visit the reserve you won't be able to see the birds up close, but there are high-powered binoculars you can use for free. The reserve is part of Taijiang National Park.
To get to the reserve, head north up Hwy 17 from Tainan and look for the English signs around the Km162 mark after crossing the Zengwen River. You could also contact Taiwan Ecotours for private tours.