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The charm of Chimney swifts

Nature's Notebook

Hearing a cacophonous sound from inside your chimney this summer? While I can’t promise it’s not a poltergeist, I can offer an alternative explanation: Chimney swifts.

This bizarre bird is native to Eastern North America and cousin to three other swift species that are found out West: White-throated, Vaux’s, and Black swifts. Despite their similarities to swallows at first blush, Chimney swifts (and their relatives) are members of a completely different family and thus bear no close relation. In fact, swifts are the only members of their family (Apodidae), informing us that they bear no immediate relation to any other bird species worldwide.

Chimney swifts (Chaetura pelagica) are cavity nesting birds that adapted to using brick or stone chimneys for rearing their young since European colonization in the 1700s. They historically relied on snags and dead trees for rearing their young, which were plentiful enough to sustain the species when our Eastern forests were abundant and continuous. But once European colonists arrived, instead of experiencing population declines because of habitat destruction, Chimney swifts thrived in the advent of breeding structures that they likely didn’t have to compete with other animals over.

This in and of itself is interesting, as many animal species fail to adapt to such drastic changes in their environments in so short a time.

When we observe their features up close, we’re privy to a couple of adaptations that make these birds well-suited for dark spaces.

Let’s start with the most obvious: their sooty feather coloration. Imagine being a hungry racoon and hoping to find a quick snack near the opening of a chimney. Good luck! These birds are diurnal and thus brood their young in chimneys by night, so natural selection has fine-tuned their camouflage to render them virtually invisible in the dark.

Next, we might notice how large their eyes are in comparison to their small heads. This feature is also a nod to the birds’ proclivity for darkness, the large eye possessing an increased capacity for absorbing light in environments where light is scarce.

Lastly, when we look at the feet, we would notice the odd arrangement of toes: all four facing forward. The muscles in swifts’ feet are so underdeveloped that they’re physically unable to perch horizontally, and thus must always maneuver about vertically when not in flight.

Unfortunately, we’re seeing a decline in these magnificent bird’s population throughout the Eastern U.S.

Pesticides taint the insect prey that adult birds rely on to feed their young, and the reduction of viable brick or stone chimneys the birds require for nesting are perhaps the two greatest threats.

Climate change, however, threatens to stress local populations even further by increasing the frequency of rainstorms and their intensity, in addition to raising summer temperatures and humidity levels. The latter is of special concern because of how Chimney swifts’ nests are constructed and adhered inside the chimney.

During the breeding season, the salivary glands inside the birds’ mouths double in size, allowing the bird to secrete enough saliva to hold their humble nest of twig pieces (broken off in mid-air by their beaks) together against the interior wall. Heavy rainfall and humidity dissolve this salivary adhesive and the nestlings fall into the fireplace as a result. This is very dangerous for them, as the parent birds will discontinue feeding and brooding them.

At the Sharon Audubon Center, the wildlife rehabilitation clinic specializes in treating these birds when the nestlings find themselves in the scenario described above.

This year, we have admitted 40-plus Chimney swift nestlings from Connecticut and the surrounding states of New York and Massachusetts. We will release all viable subadults into a ‘staging’ colony in mid-August when a large flock begins to assemble in preparation for migration to the Amazon River basin, so stay tuned for a listing of our annual “Swift Night Out!” program on our website and social media pages.

In the meantime, you can help these birds by uncapping your chimney and providing breeding habitat for them, by refraining from using lawn chemicals such as pesticides (let the birds eat the bugs for you!), and by advocating for clean energy policies at the local, state and federal levels. Lastly, you can always call our facility at 860-364-0520 should you find nestling chimney swifts that need help.

Bethany Sheffer is Volunteer Coordinator & Naturalist at the Sharon Audubon Center.

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