For the Birds – Chimney Swifts
One of our most distinctive breeding birds is the Chimney Swift. Swifts are wonderfully agile fliers with long, curved wings. They have short, tapered tails leading some authors to refer to them as flying cigars. Swifts have a distinctive stiff-winged flight. The wings of a swift appear to beat alternately but actually beat in unison like all other birds.
Chimney Swifts spend most of their time during the day in flight, hawking insects. Swifts have amazingly large mouths that serve them well in capturing insects on the wing. Their method of feeding brings to mind the feeding of swallows but swifts and swallows are not closely related. Believe it or not, swifts’ closest relatives are hummingbirds.
Chimney Swifts give away their presence by their near constant twittering. You can hear a recording of these sounds at: swift vocalizations.
The genus to which the Chimney Swift belongs is Chaetura. Chaetura means “bristle tail” and refers to distinctive hair-like bristle feathers that occur at the base of the tail. The function of these bristles is not known.
Chimney Swifts generally return to central Maine in early May. Their twittering is nearly incessant then as courtship begins. Initially, four to seven swifts fly together in an oval or circular path. Then, three birds will fly together with one acting as the leader, flying ahead of the other two. Finally, two birds will court each other by flying very close together with one bird slightly lower than the second.
Faithfulness to a mate varies. In one study in Ohio, one female had the same mate for nine consecutive years. In that same study, another female had seven different mates over the nine-year period.
Before human habitations dotted the eastern landscape, Chimney Swifts nested in hollow trees and in caves. Now, virtually all Chimney Swifts nest in house chimneys. We have pretty good evidence that Chimney Swifts were widely distributed but uncommon before Europeans settled across eastern North America. The chimneys present in virtually every colonist’s house allowed for an increase in the Chimney Swift population. This information strongly suggests that nesting sites limited the population before houses began to dot the landscape.
Both mom and dad contribute to the construction of the nest inside a chimney. The nests are semicircular cups made of twigs, attached to a vertical portion of the chimney. The swifts gather the twigs on the wing with their feet and usually transfer the twigs to their bill to carry them back to the nesting site. The twigs are glued together with the sticky saliva that the birds produce from their hyperactive salivary glands. After the nest is built, the parents’ salivary glands shrink rapidly.
A Chimney Swift nest usually has four eggs; some nests may have as many as six eggs. Both the female and the male incubate the eggs; hatching takes place 18 to 21 days after incubation commences.
Occasionally, an unmated helper will assist a pair in raising the young. The importance of the third “parent” on fledging success is not known. In most bird species in which cooperative breeding occurs, the helpers are related to the papers but we don’t know if that is the case for Chimney Swifts.
By the way, the Asian delicacy, bird nest soup, is made of the nests of cave swiftlets. The swiftlet’s nest is made of pure hardened saliva.
Both parents feed the young. Sometimes, unmated individuals will assist a pair in feeding their young. Chimney Swifts are diligent parents, sometimes foraging at night to obtain food for their hungry young. Chimney Swifts raise only one brood per year.
As Chimney Swifts prepare to migrate, they often spend the night in large communal roosts. It is truly a spectacle to see 100 or more Chimney Swifts at dusk funneling into a chimney.
Swifts have an unusual arrangement of their toes, a clear adaptation to perching on vertical surfaces. A swift can point all four of its toes upward to maximize its ability to cling to a vertical surface. Ornithologists refer to such digits as pamprodactyl toes.
However, gravity is a force that is difficult to resist and sometimes swifts fall down chimneys into a homeowner’s fireplace or woodstove. If the swift is capable of flight, the bird will fly around and eventually perch on a vertical surface like curtains or even the wall. You can then slowly approach the perched swift with a coffee can, trash basket or other small container and cover the swift. Slip a piece of cardboard over the opening of the container. Take the swift outside and let it go.
[Column originally published on August 24, 2007]