Will be excibiting this next week. Its really simple, but sort of neat
I use a servo for the movement. It uses a pully system with fishing rod cable. The "sensorbird" has a small stretch sensor within it.
Its pretty robust - I had a bunch of random people try it, and nobody broke it and everyone immedeatly was able to use it. And its fun.
(and pointless, but thats sort of the beauty of it, i guess.)
its a conductive polymere. its the same stuff I use in a bunch of my other projects, like here: Building Stuff: ShadowCoat v 0.02
(at the bottom of my blog there is a tag cloud, there should be one pointing to "stretch sensor" and you'll be able to find a lot more info there, if you are curious.
glad you guys like it. I am building an upgraded version today - introducing additional birds and some randomness in the flapping - i hope to get a more organic feel by doing so...