June 2001 - Volume 62, Issue 6
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In this issue
What's Cheeping In Your Chimney
Chimney swifts adapted to settlement by nesting in our smokestacks
As a child, did you worry about things that go bump in the night? Many people, even adults, either enjoy or worry about things that go "cheep" in their chimneys this time of year.
They may have seen dark animals darting around their chimney and dropping down the shaft at dusk. Some people, hearing a raucous chattering emitting from their fireplace, grab the phone and call the Conservation Department to report bats in their chimney.
The "culprits" behind the racket in the chimney are not bats, however, but birds with a unique lifestyle. They are known by several aliases, including chimney sweep, chimney bat and chimney swallow. The correct name for this species is chimney swift. The rapid flight of the birds and their propensity to nest in chimneys account for this name.
Unless you look inside your chimney, the only way you are likely to see a chimney swift is as a flying silhouette. Their color is sooty gray. They have short, stout bodies and long, pointed wings shaped like scythes. This is why they are also called "flying cigars" and "bow and arrow."
Swifts are only about five inches long and weigh less than one ounce, but their wingspan reaches up to 12 inches.
Their tiny feet and legs serve only as grappling hooks. Chimney swifts are unable to perch horizontally like other birds. Instead, they land only on rough, vertical surfaces like the inside of a chimney or hollow tree. Their tail feathers are stiff and pointed and serve as struts, similar to the tail of a woodpecker. While vertical shafts like chimneys are death traps for other birds, they are as easy to navigate for a chimney swift as tree branches are for a flitting cardinal.
More than any other birds in Missouri, chimney swifts are designed to live in the air. They do almost everything on the wing, including all of their feeding, courting, drinking, bathing, collecting twigs for nesting and even mating. In fact, they stop flying only for night roosting and nesting. European swifts, which are related to our chimney swift, have even been known to spend the night aloft.
Chimney swifts fly with stiff, shallow wingbeats broken by short glides, often accompanied by twittering chatter. They perform tight turns with wings held up in a "V." Short, massive wing bones and long wing feathers account for their stiff, erratic wing movements. However, this apparent awkwardness does not detract from their agility. The sharp, abrupt turns performed by chimney swifts would create enough G-force to test the endurance of the best aerobatic pilots.
Though some banded chimney swifts have lived longer than 10 years, their average life span is believed to be about four years. Some researchers have estimated that swifts may fly more than 500 miles a day during the nesting season. Chimney swifts also annually travel to Peru for the winter and return the following spring. One banded chimney swift that lived for nine years is believed to have logged 1,350,000 flight miles during its lifetime.
The chimney swift is found throughout the eastern United States and is the only North American swift regularly found east of the Rocky Mountains. They historically nested in large, hollow trees, especially those with their tops blown off by wind or lightning.
As intensive logging removed large snag trees from the forests, chimney swifts had to find an alternate nesting structure to survive. They found it in the chimneys adorning the houses that cropped up as settlers pressed westward. Because they were not used during the nesting season, chimneys proved to be excellent substitutes for dead trees. Chimneys also allowed swifts to expand their range into areas that were formerly unsuitable due to lack of trees.
Today some swift pairs still raise their families in natural snags. However, their primary nesting sites are chimneys.
Recent trends in heating methods, chimney construction and maintenance have again severely reduced the availability of nesting sites for swifts. Modern homes today rely much less on wood heat, and a large percentage of homes have no chimneys. Chimney caps also block swifts from many chimneys. In addition, many chimneys are now constructed with metal liners that lack the rough surfaces swifts need for roosting or attaching their nests. As a result, chimney swift numbers have been declining throughout much of their range and in most parts of Missouri since 1966.
Although some natural nest sites still exist, the survival of chimney swifts will likely depend on the continued availability of chimneys.
Chimney swifts are versatile in their habitat use as long as nest sites are available. In wooded areas, they forage for insects above the tree canopy. They also inhabit largely open areas that have scattered woods or tree lines. Chimney swifts are equally at home in urban areas, and they're easy for any homeowner or landowner to attract.
Chimney swifts only eat insects and other invertebrates they catch while flying. These include beetles, flies, ants, termites, mosquitoes, moths and even spiders that are blown aloft. The swift's bill is tiny, but its mouth is wide and extends to the eyes, serving as a basket for scooping small prey from the air.
When they return to Missouri from Peru, chimney swifts look for suitable nesting sites in which to raise their single brood for the year. They need vertical shafts with an inside diameter of at least 11 inches. They seem to prefer shafts with a height or depth of at least eight feet. They attach their nests to the side of the shaft usually a few feet from the bottom.
Using their sticky saliva as glue, swifts construct a small nest of small twigs gathered in flight. The nest resembles a half saucer. Both sexes participate in nest building. Nests are about four inches across at the wall and protrude only two or three inches. Unlike some birds, swifts do not line the nest with soft materials.
Once the nest is completed, the female lays three to six (usually four or five) white eggs. The male assists with incubation, and sometimes a third bird, called a "helper," also assists with incubation and young rearing.
Hatching occurs after about 19 days. Compared with other birds of similar size, young swifts spend a long time in the nest. Their eyes do not open until they are 14 days old. Once they are 19 days old, the young begin to leave the nest and cling to the walls of the nesting shaft.
At this time, they become very vocal in begging for food when the adults arrive. They also exercise their wings in preparation for the daunting job of flying straight up. Young swifts leave the nest after 28 to 30 days.
Adult chimney swifts do not feed individual insects to the nestlings. Considering the small size of most of their prey, the parent swifts would quickly become exhausted trying to satisfy the appetites of their young. Instead, the parents collect a large ball, or bolus, of insects in a special pouch in their throat. The bolus of one Alpine swift in Europe was found to contain 600 insects. They regurgitate this ball to feed one young bird. In this way, they gorge young swifts a few times each day rather than feed them continuously the way other birds do.
After young birds have left their nests, they can often be seen flying with their parents, exchanging a characteristic stream of chatter.
Family groups combine to form large flocks in preparation for their southern migration. Some of these flocks number in the thousands and roost in large, industrial chimneys. At dusk, the flock clusters above the roost chimney in a swirling mass before dropping into the chimney. One September flock containing 10,000 swifts was observed entering a chimney in Pennsylvania. The author has also observed a flock of more than 50 birds entering a typical residential chimney. A flock may use the roost for a few nights before continuing its migration to Peru.
By the middle of October the swifts have vacated Missouri.
About This Article
Authors
Norman Murray is the natural history supervisor of the Conservation Department’s West Central region. He works out of the Clinton office, but he lives in Gerster with his wife, Sheila, and two sons. He enjoys turkey hunting and improving the wildlife habitat on his property. One of his biggest passions is prairie restoration.
Photos
Click to Enlarge
Swifts still nest in snag trees when available, but they're apparently comfortable in chimneys.
Swifts cling vertically rather than perching. The inside surfaces of hollow trees are natural roosting sites.