Palo Verde OTS is a large national park in northwest Costa Rica. The habitat is the Tempisque River basin and includes marshes, mangroves and dry forest habitat. I have been to Palo Verde twice, once in the dry season and once in the wet season. I had a guide during my dry season trip.
In the dry season, Palo Verde is one of the better places to see waterfowl, but even in the wet season the park is home to a wide variety of marsh birds and Guanacaste specialties.
At almost any time of year, one can find Crested Bobwhites calling from the grasses. In early morning, a walk in the dry forest is a good place to see Thicket Tinamou - but hearing them is more likely. Double-striped Thick-knee can sometimes be seen in grassy fields on the way into Palo Verde, and the lagoon in the park may have Jabiru, Limpkin, herons, egrets, jacanas, flycatchers, and other birds.
Palo Verde is also a good place for mosquitoes, so bring bug repellant. Like La Selva, Palo Verde is an OTS site (Organization of Tropical Studies). Visit their web site to find out more. Palo Verde OTS
Close by is Lomas Barbadal, a smaller refuge with a few different species along a nice shaded trail.