If you've ever watched a swirl of small birds chittering over a city or seen them pour into a brick chimney at dusk, you've met the Chimney Swift. Nicknamed the "flying cigar" for its stubby, tapered shape, it's an aerial insectivore and long-distance migrant that spends almost its entire day on the wing. They nest by clinging vertically inside hollow trees or, far more often today, chimneys. Work to protect the Chimney Swift focuses on building nesting towers and educating homeowners who may host their nests. As a family, swifts are the supreme aerialists of the bird world — their Old World cousin the Common Swift is so committed to flight that it spends an extreme portion of its life airborne, landing only to reproduce.
But the Chimney Swift is in trouble: the 2025 State of the Birds report lists it as an "Orange Alert" Tipping Point species, having lost more than 50% of its population over the past 50 years with declines accelerating in the last decade. A prime suspect is the collapse of flying insect populations, their primary food source.
Pinning down exactly how insect scarcity shapes a swift's daily life is hard because aerial foraging unfolds high in open airspace where birds and bugs are both difficult to watch. To study their response to fluctuating insect availability, researchers tagged Little Swifts (pictured above), a compact relative of the Chimney and Common Swifts, and used radar to measure how many insects were aloft each day. On days with abundant insects, the swifts flew shorter distances, visiting their colony more often and arriving earlier. The birds were able to optimize foraging when food was readily available, allowing them to spend more time at their nests to improve reproductive success.