While staying at Arenal, we saw many of these birds–the Montezuma Oropendula. They’re pretty big…the size of a large crow, maybe.

But the awesome thing about them is the sound they make. Most of the time they make a chipping sound, but then all of a sudden, they’ll roll their whole body forward with their tail up in the air, and make a sound that is exactly the sort of thing you hear when making it to the next level of a video game (hence my nickname for them). Cracked me up every single time I heard it.  This was the best sample of the sound that I could find, but it still doesn’t quite do it justice.
http://www.youtube.com/watch?v=LBMJjgAK8Zg