Taiwan will not
be a downer for birding. Easy places to reach: Yangming Shan: you can see Crested Serpent Eagles on fairly clear deays from the areas around Xiao Yu Keng (the fumorole) and higher. I have also spotted Formosan blue magpies up there on several occasions, and also in the hills of Neihu (Wu Chi Shan -5-finger mountain; sorry, I don't know pinyin or whatever you call it).
Danshui: walk along the boardwalk between Hongshulin and Danshui Stations: spoonbills hang out in there, and black drongos are commonly found on the telephone wires. On campus at Tamkang University in Danshui I commonly hear then see -with some effort (it pays to know what they sound like and then you try and locate them): Muller's barbets, Crested serpent eagles, black drongos, other species.
Actually, Muller's barbets and Japanese white eyes -both pretty birds- can be found in many places in Taipei, even downtown. Here is a video with a good look at a Muller's barbet and it's call (in this video, the one you see is communicating with another): http://www.youtube.com/watch?v=rXfAokTrRH4
I live south of Taipei up on the Linkou/Gueishan plateau, and in the community where I live I see all of the birds listed (minus the spoonbill) plus the very rare Malayan Night Heron, of which there are 2 or 3 that live in the forested hills on the edge of the area. Malayan Night Herons are not
to be confused with the common Night Heron, which can be easily found staring into the murky waters of the Keelung (Jilong) or Danshui Rivers every day.
I would say trying Yangming Shan on a weekday morning/afternoon, and also Wulai, getting off at the Cheng Kung stop and walking down to the river for a look. Your guests will be delighted with the birdlife in Taiwan.