Other than small trails around the Sirena, Los Patos, and San Pedrillo ranger stations, the Los Patos-Sirena trail is the only inland trail in the park that is maintained. The trail is listed as 17 kilometers in length, though we measured the distance between the two stations along the trail as 15.9 km. The maps below show the trail route through the park and a few of the milestones. The chart at the bottom shows that there are only 180 meters of total relief and that the trail generally descends from Los Patos through the Corcovado lowlands.
The Los Patos - Sirena trail is a relatively shallow trail compared to other passes through the Osa highlands. The highland portion of the trail in the vicinity of Los Patos is secondary forest several decades old. Original old growth begins as the topography flattens in the Corcovado basin which begins around the first Sirena river crossing, about one third of the way toward Sirena. The primary lowland forest of Corcovado is renowned for its abundance of wildlife, and unless the trail has been heavily, the average hiker can expect to see the tracks of tapirs, peccaries, coatimundis, agoutis, and a wide variety of bird species. A tremendous abundance of wildlife inhabits the forest in the vicinity of Sirena, and hikers that move quietly and pay attention are likely to see a huge abundance of wildlife, particularly early in the morning and late in the afternoon and at night.
More than any other, the Los Patos - Sirena trail is notorious for its mud during the rainy season. Between the slogs through the lowland mud, swollen creeks and rivers, and the slippery surfaces of red-clay trails, this trail can take seven hours in the rainy season while five hours is reasonable in the dry season.
The rangers require that hikers reach the Los Patos station by ten a.m. to be allowed to proceed the same day to Sirena. Hikers with guides are allowed until eleven a.m. to arrive at Los Patos. For those seeking to reach Sirena through Los Patos from Puerto Jimenez or La Palma, it means getting started from Guadalupe no later than seven on horses or six on foot, or by eight for those able to drive right to the Los Patos trailhead.
The Sirena River is only thigh high at its deepest at any of the crossings found on this trail.