High Pitched Yelp / FWEEP
This is a cry of distress. With our three parakeets, if one of them gets separated from the other two it will begin to yelp. This is sort of a "Lost! Lost!" cry, and the other parakeets will all out to it to help it find its way back home again. In fact, sometimes if Bob leaves the room after being in there for a while, the other parakeets will assume he's "lost" and start yelping for him, to help him get back to the safe home. He has to go back and tell them he's OK, that he's just going to be away for a little while, and they settle down. We call this their "FWEEP!"