SO ENDS this first of two weekends on the sense of place as exhibited in migratory creatures. We live on a planet full of restless beasts, which have two homes, and long distances between them. On the face of it, it seems a perilous arrangement, or at least a wasteful one; many perish on these long journeys, both the young and the old. And as the beloved swallows prepare to migrate here in Spain, it is impossible not to wonder about their Herculean efforts.