October arrived and the chimney swifts left, as they always do. I thought they had gone much earlier, because they disappeared when the late summer drought was at its peak. Their diet is small insects like mosquitoes, which became scarce during the drought; so the swifts had to leave the cozy environs of Emmitsburg and go to places with lakes, swamps or rivers. The September rains brought back the mosquitoes, and soon the skies over our town were full of swifts again. But all creatures must be able to read the signs of nature if they are to survive. Shorter days and cooler nights mean winter will come, and swifts keep track of such things. I saw several of them on Sept. 28; the next day they were gone, on a flight that will take them to South America. They will find chimneys, hollow trees or rocky cliffs to roost in at night until they get to the Gulf Coast; then they will fly across the Caribbean, repeatedly soaring to great heights and then sleeping lightly as they glide slowly downward, waking before they reach the sea surface. Their journey will take them to the eastern edge of Peru, at the base of the Andes Mountains, where they will spend the southern-hemisphere summer. If time and chance favor both them and me, I will see them again next April.

Chimney swifts are among the commonest, least known and oddest of our local birds. They are about five inches long, with sickle-shaped wings that spread to nearly a foot; Roger Tory Peterson, the dean of bird watchers in America, said they look like a cigar with wings. They are a dusky gray color, but few people get close enough to discern it. If you look, you can see them darting about the sky catching insects on any summer day; but they typically fly high in the air and most people don't look up there. Those who do usually mistake them for swallows, which also dart about catching insects, but in fact the two birds are not related. Swallows typically fly much lower and commonly perch on telephone wires and fences; swifts have such small, weak feet and legs that they cannot perch or walk.

Swifts were among the few animals that benefited from the colonization of America. Originally they lived in crevasses among rocky cliffs or in hollow trees, and they were not very common in this part of the country. When Europeans came, forests with hollow trees were replaced by cities and towns with chimneys, and swifts simply traded one kind of dark, hollow place for the other. It was an easy transition; the swifts have sharp claws which they use to cling to vertical surfaces, and stiff, spiny tail feathers which they use to prop themselves up when clinging, so the rough brick surfaces of chimneys were ideal for them. This new habitat also fit their life cycle; most houses had separate chimneys for heating and cooking, and the heating grates were not in use in the summer when the swifts were here.

Even their name is odd. They were named Chaetura pelagica by the great Swedish biologist, Linnaeus, who worked in the mid-1700s when little was known about bird migration. Chaetura comes from the Greek word, chaeta, which means spine, and that is a logical reference to the spiny tail feathers. However, pelagica means "from the sea," which makes no sense until you recall the old European folktale that each autumn the swallows flew out to sea and dived into the water, sinking to the bottom and spending the winter hibernating in the mud. Linnaeus knew the difference between swifts and swallows, but bird migration was not understood in those days, so he assumed swifts also hibernated at the bottom of the sea. It was only around the time of his death that biologists thought of putting numbered bands on birds' legs and thus proving that they migrated hundreds of miles to southern areas in the winter.

Chimney swifts build nests of small twigs which they fasten to the inside of a chimney with a glue-like secretion from their saliva. (In China, the nests of a related species of swift are used to make bird's nest soup.) They usually produce 4 or 5 eggs, which take 18 days to hatch; it is another four weeks before the young birds are ready to fly. To leave the nest, they have to hitch themselves upwards with their claws and tail spines until they reach the top of the chimney, and launch themselves into the air by jumping off. Once airborne, they have to keep flying, because they are unable to perch and take a rest. If they run into something or fall to the ground, they are unable to walk or hop on horizontal surfaces; their only hope is to flop about until they reach a tree, and then crawl up far enough to re-launch themselves before a cat sees them. So they spend the day following their parents, learning to catch insects. When evening comes, they go back to the chimney and begin to fly in a circle like the vortex of a whirlpool; then, as if poured through a funnel, they dive down the chimney head-first. Somehow they must get turned around and grab onto the bricks; then they can inch themselves toward the nest. It has always amazed me that any of them survive.

For many years, swifts have raised their families in the chimney of the old house where we used to live, as well as several of the adjacent buildings, and I have enjoyed sitting on my porch at dusk on summer evenings and watching them go through their re-entry ritual. But it seems that there have been fewer of them in recent years. In new houses, chimneys often are absent; if present, they are lined with glazed fire-brick or metal, which the swifts cannot cling to. Even old chimneys often are capped with mesh to keep birds out. It seems that for the past few centuries we unknowingly provided a habitat for these peculiar birds; and now, as lifestyles change and construction methods modernize, we are unknowingly taking that habitat away. It is not a trivial or sentimental matter; each swift eats several thousands of mosquitoes every day, and in addition to their irritating bites, mosquitoes transmit to us a variety of old and new diseases. As we become more aware of the dangers of chemical pesticides, the decline in numbers of chimney swifts is a problem we need to be concerned about. We're in this together; time and chance happeneth to us all.