Exotic bird calls boom or squawk through the trees, now and again the undergrowth rustles with the movement of an unseen creature. We are drenched in sweat, dripping wet from head to toe; the baking sun casts searing heat into the occasional clearing but for the most part the lofty canopy traps intense humidity in the spaces below. Official signs warn of poisonous spiders, scorpions and snakes. The heavy air is full of the scents of foliage and damp earth. This is the Atlantic Forest, its million shades of green scaling every mountainside and sweeping with sumptuous colour to the very edge of the shore. The climb has been testing,…