there are a couple of places that i know of on the Central Pacific to do some birdwatching- the first is Carara National Park (http://www.costarica-nationalparks.com/cararanationalpark.html). You can hire a naturist guide for the hike.
The second is on the Tarcoles River boat tour. Known for the crocodile element of the tour, the majority of the tour is spent finding birds. about 9 years ago