And those JR's can jump VERY high, too. I've heard folks in my neck of the woods (literally) making squirrel-hunting dogs out of them.
Our 7 year old Chihuahua loves to chase them, too. She learned to stay quiet and not bark when headed for them. My stepson's Yorkie can't keep his yapper shut and has this puzzled look when he misses one by a good yard and I tell him "...if you'd stay quiet like Chica maybe you'd snag one". Nine months later and it still hasn't dawned on him....he might be "a little slow on the uptake", ya know?