The Common Swifts of Eurasia are similar to swallows in shape and behavior but are more closely related to hummingbirds than swallows. These aerodynamic birds are called “swifts” because of their fast and erratic flight. Because their feet are so week and small and they spend so much time in the air the ancient Greeks thought the birds had no feet. Their family name Apodidae comes from the Greek a, without and pous, foot.
The Peregrine Falcon is usually touted as the fastest flying bird, but that speed is measured in a dive. The Common Swift is perhaps the speediest bird in level flight at 69 miles per hour, although their normal speed is generally around 35 mph. They use their speed in a social display called “screaming parties” of 10-20 swifts during summer evenings; the purpose of this display is not clear but males and females have differently-pitched screams, so the vocalizations may have some role in the breeding cycle.
Common Swifts are champion speedsters, but there is more to their flying abilities. After about two months of nesting and raising young, they head to southern Africa and for ten months they rarely stop flying and then only for an hour or two; on migration and on their wintering grounds they spend 99 percent of their time in in the air. They eat, drink, sleep, and even mate as they depart from Europe in the fall until they return the following summer. Although they are fast, their long and thin wings are actually adapted for soaring. They maintain an altitude of 3000-6000 feet, occasionally 9000, with slow wingbeats and by flying into the wind to gain altitude. Their hemoglobin is adapted for delivering oxygen at low oxygen pressures and their red blood cells are relatively larger than those in most other bird families.
While in the northern climes, Common Swifts nest in tree cavities or crevices in rock cliffs, but as natural habitats have shrunk, the birds have adapted to use crevices in buildings such as under roof tiles and eaves. Nest material is caught on the wing, such as insect exoskeletons, spiderwebs, and butterfly wings, all glued into a nest with sticky saliva. Swifts may form long term pair bonds that last for years, returning to the same nesting site year after year, repairing the previous year’s nest which suffered from their absence of 40 weeks.
Young nestling swifts, dependent on the parents for sustenance, may endure a scarcity of food in bad weather as flying insects are scarce, but they have evolved an adaptation that gets them through this period: torpor. The young can drop their body temperature and survive for days without food and then recover and regain their lost weight when the weather improves. Most baby birds would simply perish.
The Common Swift’s breeding range is from western Europe to eastern Asia and from northern Scandinavia and Siberia to North Africa, China, and the Himalayas.