I think chirping is one of the sounds that we don't really know exactly why they do it. I have also heard that it is usually a distressed noise; however, I have had five pigs that have chirped (that I am aware of anyway) and none have appeared to be in any distress at all when doing so.
I've had two that simply seemed to love to chirp and did so quite often. One would chirp whenever the urge hit her. The other made a habit of singing to the entire herd in the middle of the night.
It seems like, from the reaction of all the other piggies that it may be a traditional sign of danger or distress - speaking from an evolutionary standpoint, as they tend to freeze and look on guard when a piggie chirps; however, with my pigs that chirpped on a regular basis, the rest of the herd reacted a little differently, sometimes getting excited, popcorning, etc.
I suppose I'm of the opinion that it is a noise that is not a common part of their collective vocabularies anymore and perhaps, for this reason, it can mean different things in different situations and circumstances, and even dependent upon the piggie.
I'm very interested in seeing your video.
