Chimney swifts (Chaetura pelagica) are small birds that are known for their chattering, twittering vocalizations. These vocalizations serve several important purposes for the birds.
Chimney swifts are migratory birds that breed in eastern North America and winter in South America. They get their name from their habit of roosting and nesting in chimneys. Chimney swifts are very social birds and fly and roost together in large flocks called kettles. Their noisy chattering is most noticeable when they form these large flocks.
Social Communication
One of the main reasons chimney swifts make noise is for social communication. Their constant twittering helps the birds stay in contact with each other when flying in large flocks. The noise lets them coordinate their flying patterns and maneuver as a cohesive unit. This likely provides safety benefits as the flock can work together to confuse or evade predators.
In addition to coordinating movement, the vocalizations are thought to convey information between individuals. Scientists who have studied swift calls believe they can indicate a bird’s location, movements, and intent. The variations in pitch and rhythm likely have meaning to other chimney swifts.
Defending Nests
Another reason chimney swifts are noisy is to defend their nests. Chimney swifts build nests on vertical chimney surfaces using twigs that they break off trees and glue into place with their saliva. These nests are highly prized and swifts will aggressively defend them from intruders.
When approaching their nest chimneys, swifts will make loud rattling and twittering sounds. These vocalizations serve to ward off predators and warn away other swifts from entering occupied chimneys. The calls announce that the nest is occupied. Swifts have been known to grapple intruders with their feet if they persist in entering the chimney.
Attracting Mates
The vocalizations of chimney swifts also play an important role in courtship and mating. Male swifts will perform courtship flights where they ascend rapidly twittering, and then dive down making a sharp chip noise. This display advertises the male’s fitness. Receptive females will respond with tweeting noises.
Once pairs form, the male and female swift with mate repeatedly giving a repeated twitter call. This helps strengthen the pair bond. The mating calls continue throughout the breeding season to maintain the bond and coordinate breeding activities.
Begging Calls by Nestlings
The sounds of chimney swifts extend beyond just the adults of the species. Once the females lay eggs and nestlings hatch, the young birds themselves join in the chorus of swift noises. Nestling chimney swifts will make loud begging calls when adults return to the nest with food.
These begging calls serve to stimulate the adult birds to regurgitate food for the chicks. The hunger cries help guide the adults to distribute the food properly amongst all the nestlings in a clutch. The begging calls are thought to be either less intense or absent if the nestlings are not hungry.
Echo Location in Dark Places
Another possible reason chimney swifts twitter so much is for echo location purposes. As the name suggests, chimney swifts spend a lot of time in dark chimneys. When inside these dark roosting and nesting spots, the birds cannot see very well. However, the echoes from their vocalizations may help them orient themselves.
The twitters and chip notes bounce off the chimney walls and return audible information about the swifts’ surroundings. This echolocation allows them to maneuver and find proper perching spots inside chimneys where they cannot see very well. Swifts that lose their ability to make sounds are less able to successfully use chimneys.
Startle Sounds and Alarm Calls
Chimney swifts also make noise when startled or sensing threats. They produce a brief sharp note when responding to loud noises or other disturbance events. These startle and alarm calls communicate danger to other nearby swifts.
Predators like hawks, owls, and raccoons sometimes try to snatch adult swifts out of the air or raid their nests. When approached by predators, swifts make alarm calls to scare off the threat and warn others. These alarm calls prompt swifts to swarm aggressively to mob the intruder.
Weather Calls
Scientists have noted that chimney swifts also make more excited twittering noises right before storms. It is theorized that they can detect drops in barometric pressure and use special vocalizations to communicate about impending weather changes.
These weather calls likely help alert the flock to seek safe shelter. Swifts nesting in chimneys are vulnerable to downpours that can flood their chimney homes. The rain calls prompt them to take cover.
Night Roosting Coordination
Roosting chimney swifts make a communal racket as they swarm into their nighttime chimney dwelling spots. This noisy settling-in process helps coordinate the flock as they jostle for positions inside the crowded chimney confines. The vocalizations allow the swifts to avoid crashing into each other in the dark, cramped space.
Once they all settle into a resting position by clinging vertically to the chimney walls, the swifts become much quieter. But if they get disturbed by a predator or storm at night, the busy chatter will again erupt as they take flight and seek new shelter.
Migration Communication
One of the noisiest times for chimney swifts is during migration seasons. In the fall, large flocks congregate together to migrate south and they chatter excitedly. Their high-pitched twittering helps keep the flock organized as they travel enormous distances to wintering grounds.
In spring, the swifts make the long migration north again. Males arrive first at the breeding sites and vocalize to establish nesting territories and attract females. The spring migration noise lets other swifts know good nesting chimneys are occupied.
Other Possible Reasons for Noise
There are a few other theories for why chimney swifts are so noisy:
- Making noise strengthens social bonds between flock mates
- Vocalizations communicate information about good feeding areas
- The sounds help swifts gauge the size of their flock
- Noise is just part of being a highly social, colony-nesting species
Overall, it appears chimney swifts are simply very vocal, social birds. Making constant noise allows them to coordinate their communal lifestyle in dark chimneys where they can’t always see each other well. The chatter serves essential communication functions that increase their safety and breeding success.
Conclusion
Chimney swifts make a lot of noise because their vocalizations play vital roles in their ability to thrive as a species. The twittering facilitates social interactions, mating, predator defense, navigation, parent-offspring interactions, and more. Swifts are highly auditory animals and their chatter is key to their success living in large, tight-knit colonies that require extensive coordination.