Christine Barnes is a resident of Northfield and a volunteer at St. Marks National Wildlife Refuge, St. Marks, Florida. Phenology is the study of recurring plant and animal life cycles, the timing of natural events, and how they are influenced by seasonal and climate variations.

Phenology, then, has to do with Joe's Pond, when on that deliciously warm day in spring, the block finally drops through the ice and winter is officially over.

Phenology also has something to do with migration.

Observing migration - first, the Monarch butterflies southbound out of Vermont last fall, now their return from Mexico, across the Gulf; second, the concomitant procession of migrating birds through St. Marks NWR; third, the Whooping Cranes' northbound departure on a 1,200 mile route they saw only once from behind the wings of an ultralight - well, the whole process is truly awesome.

Why do these critters migrate? According to one source, climate, geography and competition are all factors. With climate, as the Earth warms rapidly, ornithologists note the northward creep of avian ranges. Geography: some researchers say that continental drift gradually pulled breeding and feeding grounds farther and farther away from each other, so birds had to travel to compensate. Competition - too many in one place for the food available, perhaps. Whatever the cause, whatever the mystery, we do not know all the answers. But this we know: it is a brutal process, and millions die.

Last year, we volunteered at a refuge in Texas near the Gulf Coast. It was late March, and the early birds were just beginning to arrive from Mexico, and Central and South America. There were few at first, but more each day, and then, the cold front snaked in on its icy belly, smack in the middle of the landfall for thousands of swallows. Barn Swallows, Cave, Northern Rough-winged, and Tree Swallows fell - across beaches, dunes, highways and parking lots. Many died immediately. Some were too weak to fly. For the strongest few, we opened heavy equipment garages so they could take refuge for the night. But the next day, the bitter cold persisted. More birds came in, and for three days, after a 500- mile journey across water, no insect stirred, no morsel to eat - just the raw challenge of survival. We stuffed live birds into our jackets to keep them warm. We breathed warm air onto their bare-bones, devoid of any residual fat for energy. They stacked high in corners of buildings for warmth, and the sacrificial bottom layers suffocated in the night. This ugly event is called a 'fallout', and the word is far too polite for the devastation we witnessed.

This year, while standing with a group of birders near the bay at the refuge, a Ruby-throated Hummingbird, bound for your feeder, no doubt, flew into the gathering as though tipsy - out of balance, unsteady and directionless, it nearly ran into the people nearby in its frantic search for nectar. We watched its struggle, and after a while, it flew drunkenly on down the levy, still diving to sip hungrily from every tiny blossom on the way.

On the refuge road, we stopped the car in the middle of a feathered feeding frenzy - swallows again. The road surface was collecting the sun's warmth, drawing insects, and we marveled at the dance around us as 50-60 swallows swarmed and swallowed whatever moved in front of them.

Some birds come into the refuge and stay for a few days to regain their strength. Just in: a few Eastern Kingbirds, Eastern Wood-Pewee, Great Crested Flycatchers, Barn and Northern Rough-winged Swallows, and hummers.

At home, of course, there are happy endings when the returning Red-wing Blackbirds' raucous "chuurrhhh" rises over the marsh from dawn to dusk; or the first Robin's song graces the yard; or when the jewels of the woodlands, the decorative, colorful warblers, flit among the branches. These are the lucky ones. We have no way of knowing how many perished over water along the way.

But here, on a soft, sweet, gentle mid-April day, the swallows dance and sway as though beribboned on a giant maypole in the sky. Monarchs drift along on seaside zephers and sip at the cup of the growing abundance of wildflowers. Perhaps the coming days will be forgiving, and the south wind will carry gently these voyageurs on their homeward journey.