La Selva OTS is a popular destination for lowland Caribbean birding. As a biological reserve of some importance, there are many researchers there. There are guided walks in the morning, and a birding walk at around 5:45 am.
Good birds abound at La Selva. Just walking to the research station from the parking lot, you might see three species of honeycreeper, several hummingbirds, and birds like Plain-colored Tanager. La Selva is also a good place for seeing Fasciated Antshrike and White-ringed Flycatcher around the station. Rufous Motmot and perhaps a Great or Slaty-breasted Tinamou can sometimes be found on the trails. Around the La Selva vicinity is one of the best places to see the endangered Great Green Macaw - usually as a fly-over. I've also had great looks at Semi-plumbeous Hawk on two occasions and a lengthy look at a Collared Forest-Falcon on another. La Selva OTS is highly managed, so you might read up on all the rules and make sure you have a lunch ticket in advance if you plan to stay that long.
Nicaragua Seed-Finch - Greg Lavaty
Collared Aracari - Greg Lavaty
There are some accommodations in the La Selva area with birding habitat. I have personally stayed at the more upscale Selva Verde Lodge, the mid-priced LaQuinta Sarapiqui, and the cheaper Tirimbina Lodge. The Selva Verde Lodge has their own guides that can be hired to bird around the lodge property. It's a good place to see the endangered Great Green Macaw flying over or a Sunbittern along the river. Tirimbina Reserve can only be described as "adequate" in terms of accommodations and food but does have some deep forest habitat and a good trail system. I did have a Snowy Cotinga on one of the trails, but birding at Tirimbina can be feast or famine. Other budget places like El Gavilan can be found in close proximity to La Selva OTS and they do cater to birders with their use of fruit feeders. In the proper season, these feeders can produce Dusky-faced Tanager. Many birding tour groups stay at the mid-priced LaQuinta Sarapiqui (my recommendation) which is a step up from the budget accommodations. It is close to La Selva and has good surrounding habitat.
La Selva OTS Field Station - Jim Peterson