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Waiting for the train at the Central Street Metra platform on any warm late spring or summer morning, I can entertain myself by trying to count the small, dark birds with long stiff wings performing aerial dynamics. High in the sky, banking and turning, alternating rapid wingbeats and glides, chattering, mouths open, they are catching insects. These are chimney swifts (Chaetura pelagica), known to Audubon as Chimney Swallows or American Swifts.

Individual chimney swifts can catch more than 1,000 insects a day. They spend virtually all day on the wing, occasionally coming down to earth. With their weak feet, they are unable to perch like song birds. They may dip briefly in the water for a bath or drink or to snatch an insect on the fly, their bills barely touching the surface. They may flutter at leafy branches to flush insects, or pick insects off leaves, or skim insects above recently mowed lawns. Their favorite meals include caddisflies, mayflies, house flies, beetles, wasps, bees, ants and true bugs.

At night, they finally come to roost, using the spiny projections from their tails and their strong, sharp claws to cling to rough vertical surfaces, usually inside a chimney or tightly tucked into a crevice, where they are protected from the rain and dramatic changes in temperature. Poet Mark Jarman writes, “To them, there are two worlds – / The soot-thick shaft and the silky bowl of sky.” 

Male and female chimney swifts look alike. They are small, sooty grey to black above, with slightly paler throat and chest. Their long narrow, pointed, wings extend well beyond their short tails.

Chimney swifts are gregarious birds of the western hemisphere, breeding in southern Canada from mid-Saskatchewan to Newfoundland and throughout the eastern part of the United States. Until 1944, their wintering grounds were unknown. Over many years, numerous bird banders attached numbered metal bands to the legs of thousands of individuals and sent them off, hoping their recovery would end the mystery. On Aug. 1, 1944, Ben Coffey, Jr., stationed at Fort Sill, Okla., was astonished to received notice that his hope had been realized. Thirteen chimney swifts had been recovered in Peru, five of which he had banded over the years, The bands had been turned in to the American Embassy at Lima in December, 1943, by a student at the Library School of the National Library, who had received them from a friend who had, in turn, received them from “the Indians,” who had reportedly killed them. Coffey surmised that the birds had been roosting in one or more hollow trees and that the Indians had “built a smudge fire in the base, thus suffocating them and causing them to come down en masse. …” He suspected the “bands may have been accumulated over a period of several years, perhaps delivered to and held in awe by some chieftain or ‘medicine man’ and finally brought in to the settlements.”

This discovery confirmed that chimney swifts are long-distance migrants. They migrate during the day, collecting in the southern U.S. in huge variable flocks that can number more than 10,000, crossing the Gulf of Mexico and Central America until they arrive at the upper reaches of the Amazon in Peru, northern Chile or northwestern Brazil. They return by roughly the same route in spring. They are faithful not only to their mate, for life, but also to their same breeding spot in the previous year’s chimney.

Chimney swifts breed at two years, occasionally younger. They court in the air in good weather. Courtship includes a complex choreography of different chases: “Trio-flying” (one female and two males); loose groups of from four to seven birds flying at great heights with specific leaders and followers; loud “chittering”; and “V-ing,” a bonding flight between a pair, the rear bird first abruptly snapping its wings upward into a V-shape.

Nesting is a family affair, and they keep their distance from other pairs. Both sexes choose the nest site and build the nest, a half-saucer constructed of dead twigs collected by the birds while in flight, then glued together and onto the wall with the birds’ saliva. They protect it fiercely. Clutch size averages four eggs. Both sexes take turns incubating them for an average of 20 days. Young are about 29 days old when they take their first flight. As fledglings, they may return to the next for a week, after which they are on their own. About 200 unmated birds may roost for the night in a single chimney.

Before Europeans arrived and began building structures with chimneys, swifts roosted and nested in large-diameter hollow trees, particularly sycamores, and probably caves. Swifts were noticed switching to chimneys as early as 1672 in Maine. Inside, they may cluster several deep, their heads under the above bird’s wing.

Since the 1960s, researchers have noted a decline in chimney swifts, largely attributed to newer chimneys with smooth interior walls and the demolition of old or abandoned buildings that provided rough surfaces. Writers advocate education of homeowners and chimney sweeps to leave nests in place despite the cacophony associated with nesting (there is only one nest per chimney), plus the construction of artificial nesting towers, in order to conserve this species.

Thousands of swifts may funnel to roost in a single chimney on an August evening as they gather for fall migration. To watch is to witness one of the enthralling wonders of the natural world. Anyone who has noticed an Evanston chimney that draws roosting swifts is urged to contact the RoundTable.