A quadrocopter would probably be a better bet for hovering/stability

http://www.quadrocopter.us/

I don't know how well those fly at ~650ft (he was consistently around this altitude in later videos). Perhaps a traditional RC helicopter might work as well, but the noise would probably be a problem (I think he has electric planes).

However, if you just want to get rid of the pigs, not kill them, I could imagine that you could do pretty well herding them with a loud RC helicopter... perhaps even herd them into a trap or kill-zone.

Fair point. I am not 100% sure how high these fly; but you can put together an open-source arducopter for a lot cheaper than in that link (about $300 or so) and they can be programmed/automated.

So if you could get them high enough for the noise not to be a big issue, and to give them a reasonable coverage with the camera, you can easily put a few of these up in a network on autpilot (with way points) and just watch several screens at once.

The stability is normally poor, even with a tethered balloon, depending on wind conditions.

It also appears, from the guy's videos, that he has a large area of ground to cover, and with the limited optics and image resolutions he's working with, a tethered balloon wouldn't be very functional.

He should just stick with his plane idea.