by Patrick McShea
In urban, suburban, and even rural areas of southwestern Pennsylvania, the high-pitched twittering cries of circling Chimney Swifts create a soundtrack for summer days. The birds’ aerial maneuvers are a mix of rapid wing beats and dynamic glides, and much of the action relates to feeding. Chimney Swifts eat on the wing, using their unusually large mouths to capture up to 5,000 flying insects per day. (A summary of a Powdermill Aviation Research Center study of the birds’ diet preferences can be found here: Chimney Swift Research – Powdermill Nature Reserve.)
When observed overhead, passing swifts are frequently described as resembling “flying cigars,” a visual analogy attributable to the birds’ five-inch-long, tube-shaped bodies, comparatively long, narrow wings, and muted grey-brown plumage. Our region is part of the species’ summer range, an enormous portion of eastern North America stretching from the Gulf Coast to just north of the Great Lakes. In South America, an equally large region of the upper Amazon Basin in Peru, Ecuador, and Brazil supports the population during the winter.
The architectural reference in the species’ common name alludes to commensalism involving birds and people that dates to the European settlement of eastern North America. As a biology term, commensalism denotes situations in which one species obtains benefits from another, without harming or benefiting the provider. Historic records indicate that before colonial times the species now known to science as Chaetura pelagica used hollow trees for roosting and nesting. Accounts in New England of the species nesting in chimneys date to the 1670s, and along the Atlantic coastal plain the birds’ exclusive use of chimneys for nest sites was established by 1800.
Within hollow trees and chimneys, sheltered interior walls meet the birds’ requirements for nesting and roosting. Chimney Swifts are unable to perch. Instead, they cling to vertical surfaces with their feet, and use the stiff shafts that protrude from the ends of their tail feathers as a brace. For nests, swifts collect branch-end twigs with their feet, in-flight, then use their quick-drying adhesive saliva to construct a narrow platform with the tiny sticks on an interior chimney or tree cavity wall.
In his landmark 1940 publication, Birds of Western Pennsylvania, CMNH curator W.E. Clyde Todd summarized the species’ association with chimneys as “more than accidental and connotes a remarkable adaptation to the changed conditions brought about by civilization.” In the eight decades since, changes in the built environment of modern civilization have become less welcoming to Chimney Swifts.
The population of Chimney Swifts has declined over 70% since the 1960s. Although reductions in flying insect abundance, along with still undetermined threats during migration and on wintering grounds, appear to be critical factors in the decline, potential nest and roost sites have also decreased due to the widespread practice of capping viable chimneys and demolishing those no longer in use.
In 2013, the Audubon Society of Western Pennsylvania (ASWP) launched a regional initiative to publicize the species’ plight and address reductions in Chimney Swift nesting and roosting habitat. The 106-year-old conservation organization has since led a broad coalition of partners in an ongoing effort to construct, install, and monitor more than 150 Chimney Swift towers at appropriate locations in southwestern Pennsylvania. Although Chimney Swifts are known to fly and roost in large flocks during migration, the birds’ behaviors are far different during the breeding season. Only one pair will nest in a chimney or tower, and research indicates the same pair will return to the same nesting location in subsequent years.
The design of these sturdy towers, which mimic actual chimneys, is based upon construction plans detailed in the 2005 publication, Chimney Swift Towers: New Habitat for America’s Mysterious Birds, by Paul and Georgean Kyle. The couple are project directors of the Texas-based Driftwood Wildlife Association’s North American Chimney Swift Nest Site Research Project, an all-volunteer effort to expand public awareness about the beneficial nature and the plight of the species.
At sites where ASWP offers regular programming, five towers were constructed of stone to enable the structures to also function as entrance signs for the facilities. In Allegheny County’s seven parks, 12-feet high kiosk-style towers constructed of lumber, shingles, and other roofing materials are now familiar landscape features. Through a partnership with Allegheny County, the Allegheny County Parks Foundation, and the Peaceable Kingdom Fund of The Pittsburgh Foundation, a total of one hundred towers, most bearing colorful informational panels, have been installed to make these public properties more welcoming to Chimney Swifts.
Observations of Chimney Swift activity near any of the towers can contribute to the ongoing evaluation of this regional conservation initiative. Allegheny County Park Rangers have been monitoring towers within the parks where they serve, and towers elsewhere are monitored by ASWP staff and volunteers, however wider public participation is welcome. For more information about Chimney Swift conservation, including a map of tower locations and an online form for reporting observations, please visit the website of the Audubon Society of Western Pennsylvania.
Patrick McShea is an Educator at Carnegie Museum of Natural History.
Carnegie Museum of Natural History Blog Citation InformationBlog author: McShea, Patrick
Publication date: August 5, 2022