To my suprise, Camp 41 actually had a pool, a small dam across a clean, clear stream—and in the middle of the rainforest as I plunged my head under the surface, the water—at first—was almost shockingly cool! The INPA-Smithsonian team runs courses here for young biologists from across the continent.

Usually there’s a generator to re-charge batteries for the laptops, though today it wouldn’t work, and just one lantern lit the simple but well-maintained camp site. You radio back to base twice a day to report all’s well, or call up supplies to be added to the next two-and-half hour trip out, but it’s really just a place to rest after 14 hour days of sweating through the forest, studying dung-beetles, bats, frogs, trees, ants.

And it was here, after a refreshing drink prepared from exotic juices by the mateiros, that an early night for all was interrupted by those amazing howling sounds.