Reading back over field notes, I am amazed at the surprises I've forgotten. Each day offers so much. For instance, this evening in 1976 brought rain, then sleet, and finally snow to the tune of thunder and lightning, all in one hour. Overnight, the air temperature dropped forty-five degrees to freezing. Two inches of snow covered the ground by dawn; and our two yellow-billed cuckoos, the latest ever summer resident birds, were gone. Did they die or migrate? They'd been seduced to stay late by abundant berries and warm, Indian summer weather.

Such singular events are noteworthy, but it is repeated patterns or changes in them, verified over years, that are the critical messages to remember. Ordinarily, the theater's directors dismiss actors such as late-lingering cuckoos because they don't perform properly in altered scenes. Occasionally, though, those actors survive and reproduce genes that allow their offspring to act in new scenes such as warmer environments. New parts for seasoned actors or their replacements result from natural selection, which can keep things on track or redirect the play.