title: Annual 10-Month Aerial Life Phase in the Common Swift Apus apus.
abstract: The common swift (Apus apus) is adapted to an aerial lifestyle, where food and nest material are captured in the air. Observations have prompted scientists to hypothesize that swifts stay airborne for their entire non-breeding period [1, 2], including migration into sub-Saharan Africa [3-5]. It is mainly juvenile common swifts that occasionally roost in trees or buildings before autumn migration when weather is bad [1, 6]. In contrast, the North American chimney swift (Chaetura pelagica) and Vaux's swift (C. vauxi) regularly settle to roost in places like chimneys and buildings during migration and winter [7, 8]. Observations of common swifts during the winter months are scarce, and roost sites have never been found in sub-Saharan Africa. In the breeding season, non-breeding individuals usually spend the night airborne [9], whereas adult nesting birds roost in the nest [1]. We equipped common swifts with a micro data logger with an accelerometer to record flight activity (years 1-2) and with a light-level sensor for geolocation (year 2). Our data show that swifts are airborne for >99% of the time during their 10-month non-breeding period; some individuals never settled, but occasional events of flight inactivity occurred in most individuals. Apparent flight activity was lower during the daytime than during the nighttime, most likely due to prolonged gliding episodes during the daytime when soaring in thermals. Our data also revealed that twilight ascents, previously observed during the summer [10], occur throughout the year. The results have important implications for understanding physiological adaptations to endure prolonged periods of flight, including the need to sleep while airborne.
authors.affiliation: Department of Biology, Centre for Animal Movement Research, Lund University, Ecology Building, 22362 Lund, Sweden. Electronic address: anders.hedenstrom@biol.lu.se.
authors.forename: Anders
authors.initials: A
authors.lastname: Hedenström
authors.affiliation: Department of Biology, Centre for Animal Movement Research, Lund University, Ecology Building, 22362 Lund, Sweden.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Norevik
authors.affiliation: Department of Biology, Centre for Animal Movement Research, Lund University, Ecology Building, 22362 Lund, Sweden.
authors.forename: Kajsa
authors.initials: K
authors.lastname: Warfvinge
authors.affiliation: Department of Biology, Centre for Animal Movement Research, Lund University, Ecology Building, 22362 Lund, Sweden.
authors.forename: Arne
authors.initials: A
authors.lastname: Andersson
authors.affiliation: Department of Biology, Centre for Animal Movement Research, Lund University, Ecology Building, 22362 Lund, Sweden.
authors.forename: Johan
authors.initials: J
authors.lastname: Bäckman
authors.affiliation: Department of Biology, Centre for Animal Movement Research, Lund University, Ecology Building, 22362 Lund, Sweden.
authors.forename: Susanne
authors.initials: S
authors.lastname: Åkesson
mesh_terms: D061725:Accelerometry; D000222:Adaptation, Physiological; D000349:Africa; D000818:Animals; D001717:Birds / Q000502:physiology*; D002940:Circadian Rhythm; D005426:Flight, Animal; D000071421:Life History Traits; D012621:Seasons
keywords: Apus apus; accelerometry; aerial life; common swift; dusk ascent; endurance flight; flight activity; geolocation; roost; sleep