The Chimney Swift (Chaetura pelagica) is a small, sooty-gray bird often described as a “flying cigar” due to its streamlined shape and long, slender wings. This highly aerial species spends the majority of its life in flight, a behavior directly linked to its specialized diet. The Chimney Swift is an obligate aerial insectivore, meaning its entire food source consists exclusively of flying insects captured while on the wing.
The Core Diet: Aerial Insects
The Chimney Swift’s diet is composed entirely of small airborne invertebrates, often referred to as “aerial plankton.” Up to 95 percent of their food consists of flying insects, with the remainder being airborne spiders drifting on their threads. Research confirms swifts show a preference for certain prey, even when those insects are not the most abundant. Common prey includes true flies (Diptera), small beetles (Coleoptera), and true bugs (Hemiptera). They also consume winged ants, wasps, mayflies, stoneflies, and aphids, adapting their consumption to the seasonal availability of swarming insects.
Hunting and Feeding Behavior
Chimney Swifts capture their food exclusively while in flight, a behavior known as aerial foraging. They possess wide, gaping mouths that function like nets, scooping up small insects as they fly through the air. While they often forage high in the sky, they fly lower during damp weather, which causes insects to descend. When feeding young, adult swifts use saliva to compact captured insects into a small, sticky bolus. This bolus, a concentrated package of protein and fat, is then regurgitated to the nestlings, allowing parents to provision a large volume of food in a single trip.
Ecological Role as Insect Controllers
The specialized diet of the Chimney Swift gives them a significant role in regulating local insect populations. As obligate insectivores, they exert continuous pressure on the flying insect community throughout their breeding range. They are particularly effective at consuming nuisance species, including mosquitoes and gnats, providing a natural form of pest control. A single pair of adult swifts raising three young may consume the weight equivalent of 5,000 to 6,000 housefly-sized insects daily. This immense volume highlights their impact, as swifts also help suppress populations of agricultural pests, such as certain beetles.