The spring migration of birds gears up and winds down rapidly -- just a matter of a few weeks. I really enjoy this time-traveling exhibit of modern art and know-how. Ambling in the cool dawn, enjoying a thrush serenade and feathered "rainbows," I recount the passing parade. Species richness triples abruptly from thirteen to forty-two between mid and late April, increasing to a peak of forty-seven in the first week of May, and declining to thirty-nine species this week. I can expect fifty-three species altogether, but I'll be lucky to find seven by late this month and in early June.

Seasonal migration is nature's cycle but not the decade-long decline of migrants that winter in the tropics. I first noticed this ominous pattern in the mid-1980s. Thankfully, the common trio of Swainson's thrush, least flycatcher, and Nashville warbler remains, but in declining numbers, and in the 1990s I rarely see bay-breasted, cerulean, or golden-winged warblers. Yet winter residents, also migrants, cycle up and down in numbers -- white-throated sparrows, dark-eyed juncos, and American goldfinches, for instance -- while permanent residents increase. Is my counting correct, or have I succumbed to the doomsday fever that infects many naturalists these days?

Unhappily, the trends are real according to my teachers. Screech owls cache birds in tree cavities for later eating and are unbiased census takers, because they follow the rules of natural predation and capture what is easiest and most abundant. Since the mid-1980s neotropical migrants in owl larders have declined steadily, while owl numbers have cycled. The concomitant cycling of stored winter residents and the increase in stashed permanent residents also parallel my visual census. Causes for the neotropical decline remain to be sorted out but include damage and destruction of all habitats -- tropical winter, temperate breeding, and stopover.