Palo Verde National Park
The dry season from November until March. With the first rain in April tens of thousands ducks get attracted.
Book a boat trip for the afternoon on Rio Tempisque; it's an excellent place for birding. Ask in your accomodation if they can recommend a good guide or boat tour. We were lucky having the boat for us only. We saw the Boat-billed Heron, Roseate Spoonbill, Tiger Heron,Turquoise-browed Motmot, Parakeets, Green Iguana, Howler Monkeys and more. It was a highlight of our vacation.