The Chimney Swift (Chaetura pelagica) is a small, sooty-gray bird often described as a “cigar with wings” due to its distinctive shape and rapid flight style. Unlike most birds, swifts cannot perch upright on branches and instead cling to vertical surfaces, historically inside hollow trees, but now primarily within urban chimneys. They spend almost their entire lives airborne, feeding, drinking, and even bathing in flight. This highly aerial existence means their vocalizations are a primary way they communicate with one another across open sky. Understanding the unique acoustic quality of its calls is the simplest way to identify this fascinating urban resident.
Description of the Chittering Call
The primary sound produced by the Chimney Swift is a distinctive, high-pitched vocalization often referred to as a “chittering” or “twittering” call. This sound is not a song but a social contact call, consisting of a rapid-fire series of short, sharp notes delivered in quick succession. Its acoustic quality is dry and clicking, sometimes sounding almost metallic or buzzy, like an insect’s rolling twitter. The notes are high-frequency chips, and the speed at which they are strung together gives the call its unique, staccato texture.
The pace of the call is extremely fast, making it sound like a continuous stream of sound rather than individual chirps. A typical call sequence lasts about three seconds, though it is repeated frequently, especially when the birds are flying in groups. This constant vocalization acts as an aerial locator, helping swifts maintain group cohesion while they pursue airborne insects.
When a single swift calls, the sound is clear and sharp, but when multiple birds are flying together, the combined effect is a continuous, loud, undulating chatter. Analyzing the rate of the chip notes suggests they provide information about a bird’s location, helping to coordinate the movements of the group without the notes overlapping.
How Location and Activity Change the Noise
The context of the swift’s activity significantly alters the perceived volume and character of its vocalizations. While foraging high in the sky, the chittering call is constant but attenuated by distance, blending into the general background noise of the urban environment. These flight calls are typically a steady stream of communication aimed at maintaining contact and synchronizing aerial maneuvers.
The sound changes dramatically when the swifts are near or inside a chimney, which acts as a powerful resonating chamber. When a large group of swifts gathers to enter a communal roost at dusk, the collective chittering intensifies into a loud, swirling, almost deafening din just before they funnel down the flue.
Within the chimney, the activity of a nesting pair also produces unique sounds. Adult swifts feeding young cause constant, loud chirping that can be heard clearly from inside the house, especially when the nestlings are older. The movement of the birds clinging to the vertical walls can also generate a distinctive, dry rustling sound. If disturbed while roosting, they may slap their wings against their bodies or the flue wall, creating a sudden, loud booming noise intended to startle a potential predator.
Identifying Swift Sounds Versus Other Animals
Distinguishing the Chimney Swift’s vocalizations from other house-dwelling pests relies on both the quality and the timing of the noise. The swift’s call is a dry, clicking chatter, which is markedly different from the sounds of mammals that might inhabit a chimney or attic. Squirrels and raccoons typically produce a combination of heavy thumping, scraping, and gnawing sounds, along with heavier, more guttural vocalizations or squeals.
The swift’s chittering is often confused with the clicks of bats, but key differences exist. Bat vocalizations are high-frequency clicks, primarily used for echolocation, and are usually much quieter and often inaudible to the human ear indoors. Furthermore, swifts are diurnal, meaning their loud, continuous chattering is heard most frequently during the day, whereas bat activity, and consequently their vocalizations, are concentrated around dusk and dawn.
The swift’s rapid-fire chitter is also distinct from the calls of other cavity-nesting birds, such as House Sparrows or European Starlings, which have more typical, varied chirps, whistles, and squawks. If the sound is a persistent, mechanical-sounding chatter emanating from inside the flue during daylight hours, the culprit is almost certainly the Chimney Swift.