Open the door to this dazzlingly elaborate installation, and heavy air instantly steams up your glasses, lush foliage drips moisture on your head, and tropical birds swoop madly across your path. The brilliant premise of Forest Canopy, on permanent view in the Woodland Park Zoo's Tropical Rain Forest building, is that the viewer is on a boardwalk high above the jungle floor. The site's design, with its nautical ropes and geodesic-dome ceiling of frosted glass, seems to slyly reference both Trader Vic's and Battlestar Galactica. But sit for any length of time on one of the sturdy benches, and the birds will soon let you know that the place is all theirs. The blurping-gurgling-buzzing ruckus they raise sounds more like a demented electronic choir than any received notion of birdsong. Canopy reveals its deep Dadaist sympathies with the addition of children, who troop through at random intervals to add their own commentary and non sequiturs to this rich and surprising cacophony. As one of them said when faced with a South American yellow-rumped cacique, "I want my nickname to be Manny."