Seriously.. small scope - something like a straight through Bushnell spacemaster or a Nikon fieldscope 60mm with no more than a 20x wide angle lens on a shoulder pod and you can't go wrong. Not used one in a rain forest.. but I do use that set up to ID high flying migrants which has to be as difficult!
You can track flying swifts without a problem and its as fast as bins!
I'm almost never without mine - hence the state of it! - Nearly as bad as my shoes :)
Last Cheshire Pied Wheatear (313) last Red Rocks Subalpine Warbler (260), last Garden Bonaparte's Gull (209), last Self-found Citrine Wagtail (294)