On Bonnie Brae in the Outer Sunset, two birds fervently guard their nest. Passing within ten feet once was a transgression. Passing twice was unforgivable.

Taking turns, they swooped at my head, screeching and scratching. Ducking, I turned onto Country Club Drive. They followed. In fact, they continued to follow for at least half a block until I received some advice from a neighbor.

Giving a knowing glance, he put down his trash bag and gestured with flailing arms. I followed suit, and the parents quit diving at least. But they followed for blocks, flitting from house to house, aggressively cawing and beating their wings.

If birds could learn lessons, I would have gone back to take the eggs.