I've been to the zoo twice now. This video is a mixture of clips from both occasions. The high pitch sound is the "Semi" (Cicadas) which constantly make noise during the hottest month of summer. It's like a constant high pitch static noise at a high volume ALL THE TIME.
Some things I really enjoyed at the zoo are the polar bear, the lesser panda and its babies, and the rabbit roundup at the end of the video.
And some pics!