Chimney swifts (Chaetura pelagica) are called that for good reason. These birds fly with great speed and roost and build nests in chimneys. Or at least they used to until the 1960s, when chimneys began to be capped or lined with metal, making them too smooth or inaccessible for chimney swift roosting sites.
Why do chimney swifts live in old chimneys? It’s because their feet are built differently. Most birds have three toes that point forward and one that points backward. This helps birds grasp branches and hop along the ground. In chimney swifts, that backward-pointing toe swings forward. Their four forward-facing hook-like claws help them cling vertically to rough surfaces like brick walls and hollow trees. The short toes cannot grasp a branch like other birds. It’s also why these swifts cannot walk or hop on land very well. Their stiff tail feathers with projecting spines act like a diagonal brace to hold the clinging birds in place.
Where did these birds live before there were chimneys? According to artist and ornithologist John James Audubon, who in 1834 called the bird a chimney swallow:
Since our country has furnished thousands of convenient places for this Swallow to breed in, free from storms, snakes, or quadrupeds, it has abandoned, with a judgment worthy of remark, its former abodes in the hollows of trees, and taken possession of the chimneys, which emit no smoke in the summer season.
In Roger Tory Peterson’s 1934 seminal work, “A Field Guide to Birds,” he writes that the chimney swift “has been described as a ‘cigar with wings,’ and the description has continued even to this day, when cigar shapes have changed significantly. In the 1930s and earlier, cigars were mostly hand-rolled. The most popular cigar, the Perfecto, was thick in the middle and tapered to points at both ends — the same shape as a chimney swift. Since today’s cigars are mostly tube-shaped, a more accurate modern description of these birds might be “a blimp with wings.”
When baby swifts hatch they are the size of a fingernail and live in a tiny nest with a huge drop off. But the little birds are good at clinging and climbing. Soon they climb to the top of the chimney, where they wait for mom and dad to feed them.
Chimney swift nests, which can withstand all except the strongest of storms, are shaped like a half basket. Swifts need lots of saliva to glue a nest together, so during breeding season the saliva glands under their tongues enlarge. While on the wing, they break off dead twigs from trees and carry the twigs back to the nesting site, which they glue to a wall with their saliva. According to Audubon: “They throw their body suddenly against the twig, grapple it with their feet, and by an instantaneous jerk, snap it off short, and proceed with it to the place intended for the nest.”
When these birds are not perching, they are flying, sometimes at 60 miles per hour. They conduct most of their lives on the wing, catching and eating one-third of their body weight in insects each day. That’s 1,000 insects per day (even more when they have hungry youngsters to feed).
The history of chimney swift populations has been a tumultuous one. Chimney swifts used to nest in caves and hollow trees found in old-growth forests. In the early history of our nation, swifts adapted to human encroachment by building nests in chimneys as forests were razed for farmlands. This change in behavior helped chimney swifts thrive for a long time.
Suitable chimneys, though, are declining and have been for some time. Up to 1875 or a little later chimney swifts continued to breed abundantly in our immediate neighborhood, and very commonly in many other parts of Cambridge. Ornithologist William Brewster, whose boyhood home was at Brattle and Sparks Street (now the Holy Trinity Armenian Church), wrote: One of the pleasantest recollections of my youth is that of Chimney Swifts careering in swarms, with joyous, twittering cries, over and around our house. Although they have not yet deserted this city, we no longer see them here in any numbers, at least in early summer.
According to the North American Breeding Bird Survey, between 1966 and 2023, the chimney swift population declined by 74 percent across the country.
Brewster continues, “In my opinion, it has not been due to the spread and increase of the human population as much as to the change in landscape,” especially as older houses were replaced replaced by houses with narrow, smoothly lined chimney flues. He notes that in the farming country to the west of Cambridge, as well as about the village centers of Arlington, Belmont and Watertown, where chimneys of ancient pattern still abound, the swifts continue to reappear every season in nearly, if not quite their former, numbers.
But, according to a study in Canada, the biggest threat to chimney swift populations today is not lack of suitable nesting sites but rather a lack of insects to eat. Other birds that catch insects on the wing (swallows, flycatchers) are experiencing a similar population crash. We can help chimney swifts and other insect-eating birds by helping insect populations. Planting native species to help native insects thrive and avoiding the use of pesticides that kill insects would be a great start.
A stronger
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