By Bennett Hennessey
Serranía Pilón is easily the richest Foothill forest in Bolivia with over 309 species recorded between 500 and 900 m. Unfortunately, there is currently no easy access to the pristine forest of Serranía Pilón, making Serranía Sadiri a better option for those who have limited time or are not extreme adventurers. Serranía Sadiri has a similar avifauna but with slightly lower abundances.
A second-best alternative is bird Serranía Pilón from the main road that travels from La Paz to Yucumo and Rurrenabaque. Most of the roadside birding is in secondary forest and disturbed areas, but this can still be very productive. This is presently one of the few sites known for the new Phyllomyias weedeni Tyrannulet that Sebastian Herzog proved existed along this road. Best to bird the area very early in the morning, ideally as you slowly descend the Serranía, traveling North, towards Yucumo.
This Foothill forest abounds, with numerous canopy foraging flocks with Paradise, Bay-headed, Masked, Yellow-bellied, Green-and-gold, Turquoise, Guira, Palm, and during the right time of year, even Scarlet Tanagers. Keep your ears tuned. Follow any mixed calls or contact notes as it is probably a foraging flock. The flocks sometimes seem to be moving quickly, but they can move back and forth, so don't leave an area too quickly after a flock has seemingly left. The Paradise Tanager is the base of the majority of canopy flocks, listen for the ever-present psst-chuck-pssst-chuck sound. Also try and listen to the croaking like calls of the Red-crowned Ant-Tanager, which is the sentinel species for this areas understory foraging flock. If you hear this bird, follow its sound, as it is surely to lead you to at least a little band of travelers.
Logistics: Serranía Pilón is presently only accessible along the main road Rurrenabaque-Yucumo Caranavi-Coroico-La Paz. Coming from La Paz and the south, one strategy would be to bird the area as part of a multi-day could be visited trip from La Paz to Rurrenabaque. Alternatively, coming from the north, Serrania Pilón from the small town of Yucumo. From Yucumo, the road to La Paz travels up to 1100 m and is paved for a good part of the climb.
About 5 km after the peak of Serranía Pilón- where the road starts to go down again and a new paved section begins after a bridge- is the Pilón Lajas Biosphere Reserve Guard Station, where you can ask if any trails have been opened, also you can camp just outside their station for a little security. The roadside is best birded in the very early in the morning.
Hint: if you want to make good friends with the park guards bring them a kilo of fresh meat- these guys are on a limited food allowance. The top of Serranía Pilón is about 30 km, from Yucumo. Yucumo is a basic pull-over town, with no car rental but with two hotels, one decent restaurant and shops. Car rental would have to be done in Rurrenabaque for a car with a chauffeur (his car) or normal car rentals from La Paz.
Frank E. Rheindt advises (15DEC11) near the top of the serranía there is a side-track that forks and gives access to two different antennae. Following the track offers access to a much better secondary habitat than along the road. On this trial Frank saw the Weeden’s Tyrannulet.