Swifts are among the most aerial of all birds. When not on the nest, they spend virtually all of their time in the air. Swifts from Europe and China migrate to Africa where they rarely touch down.
Few swifts now nest in natural habitats in Europe and Britain; they have adapted overwhelmingly and very successfully to human architecture.
The short stocky humerus or upper wing bone provides the strength required to beat their wings quickly and strongly. An early ancestor of the swifts and the hummingbirds, the 52 million year old Eocypselus rowei, shows the strong upper wing bone that allows the flight characteristics of each.
Swifts are the fastest birds in level flight, attaining almost 70 miles per hour. Normal flight speeds are 30 to 40 miles per hour. At a speed of 30 mph, a swift would cover 225,00 miles in a year.
Swifts fly at night and are able to sleep in one half of their brain at a time.
Swifts mate in the air - the only bird to do so. Nest materials are acquired in flight; therefore only materials light enough to be lofted high into the air are used. The fine materials are held together with the bird's saliva.
The high concentration of saliva in some nests make them an attractive basis for soup, especially popular in Asia. Sales of swift nests account for 5 percent of the GDP of Indonesia - $4 billion per year. In order to generate these volumes, concrete nesting houses are built.
In Italy, towers are built for swifts from which a portion of the chicks are harvested for food. In medieval times, sparrow pots were used to provide nests for both sparrows and swifts, the pots having access holes for taking chicks.
Swifts gather 300 - 1000 insects at a time, returning to the nest with a ball of insects in their throat. The insects caught are large in variety, including thrips, flies, aphids, beetles, spiders, moths and mayflies. It appears that they are able to distinguish between hornets and hoverflies.
Very wet periods cause insects to stay low, starving the swifts. During such periods, they sometimes form temporary roosts, gathering in protected areas in buildings. Prolonged wet periods may cause the birds to return to Africa early.
Swifts are parasitized by a specific insect called the swift lousefly (Crataerina pallida). The pupae of this large insect are often found on chicks, but do not appear to have a significant effect on their growth.
Much of the book is devoted to the author's travels visiting swift nesting areas throughout Europe and Britain. She highlights those persons that have worked hard to assist the swifts by installing nest boxes and sound systems to attract them to the boxes.