Do Birds Sleep When They Fly?

Some birds spend most of their time in flight. They feed and reproduce in the air, but what about the night? The majority of birds sleep perched or on the ground, except for a species that would sleep by gliding at 1.5 km high, in the sky.

Common Swift (Apus apus) sitting on a branch

A considerable portion of bird species experience nocturnal rest, akin to human sleep patterns. However, there exist nocturnal species like the eider duck and the Eurasian eagle-owl, and certain species exhibit sleep during both night and day. For the remaining species, once the sun descends, avian slumber commences. Yet, the question of their sleeping locations remains shrouded in partial understanding. At twilight, one can observe starlings assembling to locate a communal nest, where they do not sleep while in flight. Much like the majority of their avian counterparts, they seek out sleep sites akin to their nesting locations.

The Common Swift: A Bird That Would Sleep While Flying

Considerable variability arises in the location and manner of sleep, largely contingent upon the specific species under consideration. Many aspects of avian sleep still remain enigmatic. Presently, we lack definitive evidence to assert that particular species engage in airborne sleep. Nonetheless, compelling suspicions encircle the common swift. This diminutive avian, known for its migratory nature, departs from equatorial Africa as winter concludes and traverses a significant span of Eurasia until summer’s conclusion.

The swift dedicates the majority of its lifespan to flight. Its legs are of such small proportions that it cannot launch from the ground. Indeed, its only intermissions occur during nesting periods, where egg incubation transpires. High altitudes serve as its perching spots due to the swift’s mode of initiating flight—plunging and capitalizing on gravity’s pull to commence flight. Juveniles, upon departing the nest, sustain approximately two years of uninterrupted flight, eschewing landings altogether.

Though definitive evidence remains elusive regarding the swift’s in-flight slumber, the concept finds widespread acceptance. Nocturnal radar observations confirm their activity; during nighttime hours, the birds congregate and appear to ‘sleep’ while circling in the air, capitalizing on temperature inversions for gliding.