The Osa Peninsula harbors 400 bird species and the last remaining old growth rainforest on the west coast of Central America, and it is the most underbirded corner of Costa Rica
By Stephan Lorenz | Published: 6/24/2011
We had just enough light to see the outline of the ragged forest canopy and edges of the clearing, but the interior of the jungle remained dark. It was April, the end of the dry season, and without fail, the first bird call of the day was the melancholy two-note whistle of the Rufous Mourner. A few minutes later, the endemic Black-cheeked Ant-Tanager chimed in with its bell-like morning song, a sure sign it was time to start down one of the narrow trails into the forest.
Scope thrown over my shoulder, I led a small group of birders visiting from the United States and Europe who had come to what is probably the most underbirded corner of Costa Rica: the Osa Peninsula in the remote southwest of the country. It harbors the last remaining old growth rainforest on the west coast of Central America and provides critical habitat for hundreds of species of birds, including about 60 that winter on the Osa and breed in the United States and Canada. WatchList birds such as Wood Thrush, Canada Warbler, and Wilson’s Plover are among them.
We walked slowly uphill through primary rainforest, keeping an eye on the path ahead. Behind a bend, I could make out the shape of a Black-faced Antthrush, barely a silhouette. It strutted with jerky movements for a few feet along open ground before disappearing into the dense undergrowth. Marbled Wood-Quails, master skulkers, called downslope. The species requires time and patience to see, but it can often be found in the middle of the day, quietly digging through deep leaf litter.
My watch barely read 6 a.m., but it was already warm and humid. After another steep section of trail, we reached a wider track used by locals to access remote gold-mining camps. Rains and horses had turned the surface into slick muck, but it was worth climbing toward more open forest. Higher up, morning light drenched tall, tangled rainforest encircling a large clearing.
Slowly walking uphill, I suddenly heard the nearly inaudible but distinct flutter of the bird we were after. We struggled to the center of the clearing and craned our necks, carefully checking the canopy of a single tree. The first bird I put my binoculars on was a euphonia, one of a group of small birds closely related to finches; the region’s six species can be challenging to identify, but before I could study this individual, movement nearby grabbed my attention. We had found our quarry.
On a bare branch in full sunlight perched a male Turquoise Cotinga — one of the most dazzling birds in Central America. It is not only beautiful but also rare, occurring only in southwestern Costa Rica and western Panama. Cotingas are thrush-size frugivores, and many species tend to be uncommon to rare. The male Turquoise Cotinga is intense glossy blue with a deep violet throat, breast, and belly. A black eye-ring and black spangling on its shoulders and back distinguish it from similar species.
Osa travel tips
When to go
The wet season lasts from late April to December. During it, bird activity can be at its highest. The dry season, from the end of December until April, is the busy season for tourism in Costa Rica, but the Osa Peninsula rarely sees crowds any time of year. Heavy downpours can occur during any month, and birding is excellent every day of the year.
How to get there
Puerto Jiménez, the largest town on the peninsula, can be reached by daily flights on Nature Air or Sansa from Costa Rica’s capital, San Jose. Or you can drive, which takes about 7-8 hours from San Jose, or take a 9- to 10-hour bus ride. In Puerto Jiménez, you can rent a vehicle or take taxis to get around. The Bosque del Río Tigre Ecolodge (www.osaadventures.com), located 45 minutes from Puerto Jiménez, is the premier birding lodge in the area.
We watched it for several minutes as it fluttered about, picking berries from a vine tangle. Then it flew off a long way, as cotingas usually do. The unidentified euphonia was long gone, but we could catch up with it another day.
For decades, Costa Rica has been a renowned birding destination, boosting life lists for visitors from all over the world. It has an extremely varied topography, supporting mangrove-lined coasts, lowland rainforest, mid-elevation cloud forest, and tussock grasslands of the high-elevation páramo. For its size — smaller than West Virginia — Costa Rica boasts an amazing biodiversity. Nearly 900 bird species have been found in the country.
The nation’s hotspots — Monteverde Cloud Forest Reserve, La Selva Biological Station, Carara National Park — are edged in, highlighted, and double-underlined on nearly everyone’s itinerary, and for good reasons. By contrast, the Osa Peninsula is relatively unknown.
Jutting out from the mainland, it encircles the Golfo Dulce, one of only four tropical fjords on the planet, on its eastern side and braces against the pounding Pacific to the west. The mountainous spine of the peninsula reaches elevations of 3,000 feet, supporting vast stretches of montane forest and patches of cloud forest. Creeks cascade through steep valleys, spilling into larger rivers that meander through lowland rainforest and swamplands before emptying into the ocean. Estuaries and coastlines are fringed by extensive stands of mangroves — critical habitat for several rare and threatened bird species.
For birdwatchers, the Osa offers a diverse and unspoiled experience, where even after several days of serious exploring, the possibilities remain nearly endless. A single day can take visitors from stalking antbirds in primary rainforest to exploring the coast for mangrove specialties, with a quick stop along roadside pastures to chase down seedeaters and other open-country birds.
It’s not a stretch to say that the peninsula harbors some of the highest biodiversity on earth. About 400 bird species have been found on the Osa, and nearly half of all plant and animal species in Costa Rica occur here. Howler monkeys move through the canopy, and humpback whales swim in the Golfo Dulce. Acclaimed conservationist Adrian Forsyth describes the peninsula as a place with “a lot of biological superlatives tacked into a relatively modest area.”
Considerable conservation work and field studies by researchers occur on the Osa. For example, the American Bird Conservancy leads an effort to conserve the mangrove habitat of the Yellow-billed Cotinga, and the Nature Conservancy supports work to save sea turtles that nest on the beaches.
Traveling birders have largely missed the Osa’s riches, mainly due to its distance from the capital, San Jose — 9-10 hours by bus — and difficult access. But major improvements to the main road and a range of comfortable accommodations make exploration far easier than in previous decades. Route 245, which runs down the length of the peninsula, has been paved, replacing the dusty pot-holed track old school buses used to test their shocks on. It remains to be seen whether the easier drive will increase tourism, traffic, and development, but it’s safe to say that the time to visit the Osa Peninsula is now.
Fortunately, immense tracts of rainforest and untouched coastline are protected within Corcovado National Park, the crown jewel of Costa Rica’s national park system. It supports sizeable populations of Baird’s tapir and the threatened Central American squirrel monkey, as well as a few jaguars. Even Harpy Eagles are reported from the park periodically, although sightings have decreased over the past decades. The greatest chance to encounter a Harpy Eagle or other large forest raptors lies within the heart of the park at Sirena Ranger Station or along any of the long trails leading through the park.
Birds of the Osa
Black-cheeked Ant-Tanager and Mangrove Hummingbird
Species restricted to southwestern Costa Rica and western Panama:Charming Hummingbird, White-crested Coquette, Baird’s Trogon, Fiery-billed Araçari, Golden-naped Woodpecker, Yellow-billed and Turquoise Cotingas, Orange-collared Manakin, Riverside Wren, Cherrie’s Tanager, and Spot-crowned Euphonia
Species with limited ranges:
Marbled Wood-Quail, King Vulture, Uniform Crake, Scarlet Macaw, White-tipped Sicklebill, Pale-breasted Spinetail, Tawny-winged Woodcreeper, Yellow-crowned Tyrannulet, Black-tailed Flycatcher, Scrub Greenlet, and Black-bellied Wren
Located near the Pacific coast, Sirena is the park headquarters and the best place within Corcovado to see wildlife. In addition, a 16-mile hike from the Los Patos Ranger Station on the eastern edge of the park to Sirena offers great birding. Here it is possible to see the raucous Red-throated Caracara, which inexplicably has declined to near extirpation within Costa Rica.
Just outside the eastern border of the park is the village of Dos Brazos, where a dozen sleepy houses clustered around a three-way dirt intersection mark the center of town. Full of friendly locals and squawking chickens, the small area has recorded an incredible 375 bird species. It is possible to see 150 species in one long day, on foot!
Primary rainforest stands atop steep ridges, while shrubby second growth and lush pastures line the Río Tigre. It is not uncommon to stand in the middle of the village and see King Vultures launch themselves into midmorning thermals creeping up the mountainsides while simultaneously having noisy pairs of Scarlet Macaws pass overhead on their morning commute.
Several range-restricted species are commonly seen in and around Dos Brazos, including the large and distinct Baird’s Trogon. Black-hooded Antshrikes are often spotted in tangles along edges of clearings, and Spot-crowned Euphonias frequent fruiting mistletoe. A unique hummingbird, the White-crested Coquette, resembling a sphinx moth in appearance and behavior, feeds high in the canopy for most of the year and typically remains undetected, but from February through April, several individuals can usually be found on specific blooming trees in the area, bouncing up and down right at eye level.
The Osa is also the premier location to see two of the three Costa Rican mainland endemics. The Black-cheeked Ant-Tanager is almost restricted to the peninsula and can be found in primary and older secondary forests, often along shady stream valleys. The Mangrove Hummingbird occurs only along the Golfo Dulce and Pacific coasts, feeding primarily from tea mangrove flowers.
The extensive tracts of contiguous primary and secondary rainforest also support large birds that have become scarce in other areas of the country, including Great Tinamou, Great Curassow, Crested Guan, and Black, Ornate, and Black-and-white Hawk-Eagles.
Birds are not the only animals thriving in the intact forest. With enough time and patience, a visitor could study monkeys, anteaters, and sloths and, with great fortune, maybe even glimpse a tapir or one of five species of wild cat. And a close inspection of the forest floor may reveal tiny poison dart frogs.
After the Turquoise Cotinga flew off, we stood in the clearing, elated, a bit out of breath, our shirts drenched. The sun had risen, and the brief but spectacular morning chorus typical of neotropical rainforests was in full swing. We listened to the distant mot-mot of the Blue-crowned Motmot, the loud song of a Riverside Wren exploding from a thicket, the whistle of Chestnut-backed Antbirds, an insectlike Golden-crowned Spadebill high up in the canopy, and the never-ending call of the Green Shrike-Vireo.
Farther down the trail, we saw Chestnut-mandibled Toucans along a far line of trees and a White-necked Puffbird on a bare snag. And Scarlet Macaws were first heard and then sailed into view, about half a dozen pairs. The Osa continues to be one of the few places in Central America where the amazing parrots can be seen daily.
Nearby, a group of a Fiery-billed Araçaris, smaller colorful cousins of the toucans, investigated a large cavity as a possible nesting site. By midmorning, activity slowed, and it was time to head back downhill. Along the way, a Great Antshrike, colored bold white and black, played more hide than seek; an unusually tame Ruddy Quail-Dove sat out in the open; and a Band-tailed Barbthroat, one of the brownish hermit hummingbirds, fastidiously tended its nest.
A place of biological superlatives
The Osa Peninsula is pristine not only because of its remote location but also because conservationists such as Adrian Forsyth have worked to preserve it. He is a vice president at the Blue Moon Fund, a philanthropic foundation that supports environmental projects in Asia and the Americas. Forsyth is also a research associate at the Smithsonian Institution, a co-founder of the Amazon Conservation Association, the author of nine books, and the founder of Friends of the Osa.
Last year, Associate Editor Matt Mendenhall interviewed Forsyth about the Osa, its birds and other wildlife, protecting the peninsula, and the state of tropical forests worldwide. Here is an excerpt:
Tell me about the Osa Peninsula. What’s special about it?
“The Osa is kind of an outlier of the Amazon [ecosystem] because it projects out into the ocean. We believe it’s probably a safe haven against climate change. If you look at tropical tree distributions, for example, a lot of Amazonian trees reach their northern limit in the Osa, not on the mainland. That’s because the Osa is almost like an island, being surrounded by the ocean.
“As a result of that peninsular shape, it’s isolated during seasons of sea-level rise, so you find a lot of endemic species that are found only in the Osa. We have birds that are restricted only to that area, like Black-cheeked Ant-Tanager, Yellow-billed Cotinga, and Mangrove Hummingbird. A lot of vertebrate taxa have evolved specifically in that area, and we think that’s because of its unique geological and climate properties.
“It’s also important because it was one of the last areas to get an access road in Costa Rica. It has the biggest intact stand of wet tropical rainforest left on the Pacific coast of Central America. It’s got the biggest intact mangrove ecosystem left on the Pacific coast of Central America. It’s got a deep tropical fjord where, for example, northern and southern humpback whale populations meet. So it has a lot of biological superlatives tacked into a relatively modest area. If you had to say, ‘What’s the most important conservation unit in Central America?’ this has got to be at or near the top.”
In a thicket, we heard the firecracker display of the Orange-collared Manakin, another species restricted to lowland rainforest of southwestern Costa Rica and western Panama. We snuck closer and peered through an opening in the dense foliage and soon found a male with black cap and wings, glowing orange collar, and yellow belly perched on a thin branch for a moment before shooting out of view, snapping its wings.
The Turquoise Cotinga is not the only cotinga found on the peninsula; it shares its range with the much rarer Yellow-billed Cotinga. Both species are regional endemics, occurring only in southwestern Costa Rica and western Panama.
The male Yellow-billed is an ethereal white all over except for a large dark eye and short yellow bill. The female shares the yellow bill and dark eye but is otherwise colored in shades of gray. The species prefers to forage and breed in the vicinity of mangroves. Currently the entire world population is estimated to be fewer than 1,000 individuals.
The Osa provides a critical stronghold for the species, and up to a dozen birds can be seen in mangroves and nearby fruiting trees in the vicinity of the Rincon River bridge at the northeastern end of the peninsula. The site has been a focus of recent research into the behavior and population size of the species.
While morning offers the greatest bird activity, late afternoon walks can be equally rewarding. Feeding flocks will often escape the hottest part of the day and congregate in shady ravines along rivers and streams. The habitats also host one of the most improbable looking hummingbirds: the White-tipped Sicklebill. Its drab green upperparts and simply streaked underparts are offset by the namesake bill, which curves down and nearly back onto itself. Its large eyes reveal its preference for dark heliconia thickets, where it feeds on the distinct large red flowers hanging from thick vines.
Heliconia swamps around Dos Brazos also harbor the Uniform Crake, one of the most secretive birds of the area. With persistence, it is possible to glimpse a crake stalking through its favored thicket.
The evenings are quiet and start early because the sun sets around 6 p.m. year-round. After a good meal, we birders catch up with the day’s bird list and notes, make plans for the following morning, or just relax and listen to the rainforest: a chorus of frogs streaming from the river, a distant Spectacled Owl hooting, and maybe the shy rustle of a mammal deep in the forest.
Protecting the Osa
Friends of the Osa works to protect the peninsula’s natural resources. It provides oversight and land stewardship for the 4,200-acre Osa National Wildlife Refuge, and it operates the Osa Biodiversity Center and other field stations for visiting biologists. It also monitors and protects endangered sea turtles and leads environmental education efforts at local schools.
Friends of the Osa
Friends of the Osa and the Wisconsin Bird Conservation Initiative offer birding trips to the Osa that raise funds for the protection of migratory bird habitat on the peninsula. Wisconsin conservationists became involved because Osa forests provide wintering habitat for 54 bird species that breed in the state, including Golden-winged and Prothonotary Warblers.
Osa Conservation Trips
Stephan Lorenz has worked as a naturalist guide on the Osa Peninsula and on St. Paul Island in Alaska. He has published several papers on bird distribution, natural history, and identification, and he has conducted field research in Jamaica, Australia, and Texas.