Osa Peninsula and Southern Lowlands
Birding the Osa Peninsula has several things to recommend it, but it is a far stretch for a car drive. Getting to any good birding location on the Osa is at least 6 hours from San Jose. The two most frequently visited places for birding are Esquinas Rainforest Lodge and Bosque del Rio Tigre Lodge. Both lodges will likely provide looks at the endemic Black-cheeked Ant-Tanager and some good birding on the forested trails.
Esquinas Rainforest Lodge is on the periphery of the peninsula closer to the main highway and is not as far a drive as Bosque del Rio Tigre. You also have a few birding sites around Esquinas within a short car drive. Bosque del Rio Tigre is a smaller operation in the heart of the Osa Peninsula, but is more attentive to a birding clientele. Both Esquinas and Bosque del Rio Tigre offer good birding. The choice may simply depend on target species.
Esquinas Lodge is a clean, well-managed lodge off Highway 2 on the road to La Gamba. Great Currasow is a yard bird on the Esquinas grounds, and birds like Rusty-margined Flycatcher is an easy bird to see on the road into the lodge. Also on the road into the lodge, we had good looks at Red-rumped Woodpecker, Crested Oropendola, Blue-headed Parrot, Isthmian Wren, Red-breasted Meadowlark, and Yellow-bellied Seedeater. Early morning on the lodge grounds produced Striped Woodhaunter, Scaly-breasted Wren, and Band-tailed Barbthroat. Along some of the trails, the Black-cheeked Ant-Tanager is usually observed regularly.
There are guides available at Esquinas Lodge, but not all guides are birding guides. I prefer a birding guide for the Osa Peninsula. Specialty birds like Red-rumped Woodpecker and Blue-headed Parrot require real first-hand knowledge of habitat around the road to La Gamba if one is to get good looks.
Bosque del Rio Tigre Lodge
Bosque del Rio Tigre is a small lodge near the town of Dos Brazos in the center of the Osa Peninsula. The list of birds around Bosque del Rio Tigre include Black-faced Anthrush, White-throated Crake, Scarlet Macaw, Bronzy Hermit, White-tipped Sicklebill, Charming Hummingbird, Black-striped and Long-tailed Woodcreepers, White-throated Shrike-Tanager, Red-breasted Meadowlark and perhaps Uniform Crake if you're there in the dry season. There are not a lot of antbirds in southwestern Costa Rica, but of the ones found on the Osa Peninsula, I saw nearly all of them at Bosque. Abraham Gallo is the on-site bird guide for Bosque del Rio Tigre and his skills are excellent. The endemic Mangrove Hummingbird can almost always be found on a short drive to the coast if Abraham is guiding.
Bosque del Rio Tigre lodge is also one of the few places (or perhaps the only place) where you can sometimes get an adequate visual sighting of a Little Tinamou. One trail produced both the Turquoise and Yellow-billed Cotinga, but observations may depend on fruiting trees. Add birds like Marbled Wood-Quail and Black-cheeked Ant-Tanager to the math, and you have a special place.
Bosque del Rio Tigre lodge is fairly small and only has minimal use of electricity - making it a true eco-lodge by design. The accommodations are spartan but clean. There may be some minimal discomfort at night if the weather is very warm. This lodge is made for the committed bio-bum, as the action is all in the surrounding habitat. But Bosque del Rio Tigre is clean, has good management, good service and good food .... and the birds are excellent.
Farther south on Highway 2 near the Panama border (but not a terribly long drive from Esquinas Lodge) are a couple of nice birding locations in a section of southern Costa Rica known as Coto 47. This area covers a few square miles, and it lies just southwest of the city of Neily. Most Costa Rican bird guides know the location. The area contains several habitat types including a large lagoon (Las Pangas), and some rice fields/grassland/savannah areas not normally seen farther north. Several Costa Rica specialties occur here. On a half-day trip, we observed Gray-lined Hawk (three different birds in a large area of broken palm trees known as finca 41), Savanna Hawk, Masked Duck, Southern Lapwing, Lesser Yellow-headed Vulture, and Sapphire-throated Hummingbird. The open area in Coto 47 is mostly flat and the roads mostly paved. However, until a good map of birding locations in this area is published, one will likely need a guided trip into Coto 47. Johan Chaves was our guide for this extension.
Corcovado National Park
Oddly enough, this huge park has little to recommend it as a birding location. Getting there is a huge problem, and of the few birds I saw, most I saw better elsewhere. We had to travel by boat to get to the park entrance, and so the only new species I got was Brown Noddy offshore on the way over. Rough seas can make the experience an added nightmare.
In my mind, the best birding in the Osa Peninsula is around Bosque del Rio Tigre Lodge and Esquinas Lodge.