In Scotland, a herd of sheep managed by a single border collie can cover the entire side of a sweeping hillside or be a small group in the garden of a highland farm. The collie takes either assignment with equal diligence, and marshals the sheep in his charge with persistence and focus. He does this without barking, nipping or threatening, but rather with care and love.

If one in the herd lags behind to taste a delicate piece of grass on the edge of the field or watch a passing hedgehog, the…