Vertebrate Zoology - V. M. Konstantinov 2011

Chordates
Terrestrial, or Tetrapod, Vertebrates — Vertebrates with Embryonic Membranes
Class Aves — Subclass Neornithes — Superorder Neognathae — Order Apodiformes

The order Apodiformes comprises 420–430 species grouped into two suborders: swifts (Apodidae) and hummingbirds (Trochili). Their shared characteristics include long, sharp wings and the fast, highly maneuverable flight associated with them. They also possess distinctive features in their Skeletal Structure and Internal Organs. The chicks are small to very small in size, with a body mass ranging from 1.6 to 200 g.

Swifts bear a superficial resemblance to swallows, with which they share much in common regarding their lifestyle (see Fig. 148). However, as comparative anatomy demonstrates, they are systematically distant, and their external similarity is the result of convergence rather than close relatedness. Swifts feed on small insects caught on the wing. They are incapable of moving along the ground because their legs are very short and all four toes point forward. The beak is very small, whereas the gape of the Mouth is exceptionally large, extending past the level of the eyes. The wings are long and sickle-shaped. They spend the vast majority of their time in the air hunting for insects. They drink and even bathe while in flight. The flight speed of certain species reaches 120–170 km/h. Their body Temperature is not as constant as that of most other birds; during sudden cold snaps, swifts enter a state of torpor, or short-term hibernation.

About 60 species are known. In Russia, the common swift (Apus apus) is the most widely distributed. In Europe, this species clearly gravitates toward towns and villages, nesting in buildings. It less frequently nests in forests, within tree hollows. In Eastern Siberia, it nests almost exclusively in forests. It brings food to its chicks in the form of a bolus of insects glued together with saliva, approximately 35 times a day.

In Southeast Asia, on the islands of the Malay Archipelago and Polynesia, swiftlets of the genus Collocalia are widespread. They typically nest in caves, often very long ones, in large colonies. The species of swiftlets that nest deep inside caves, where light never penetrates, possess the capacity for echolocation to navigate their surroundings. Some species build their nests entirely from saliva that hardens in the air. These are the so-called "bird's nests," which are considered a culinary delicacy by the local population. Other species utilize not only saliva but also small plant particles such as bark fragments, fibers, and tiny Lichens to construct their nests. Nest building is a very protracted process, taking about 40 days.

Hummingbirds form a distinct group comprising small and minuscule birds. Large hummingbirds are the size of a swallow, while the smallest are no larger than a bumblebee, with a body mass of 3–7 g. Their plumage is usually very bright and iridescent. They fly at high speeds and beat their wings so rapidly that the wing outline becomes invisible to the human eye. The wingbeat frequency can reach 20–25 beats per second, and in some species, 50–80 beats per second. In correlation with this immense muscular effort, The Heart is exceptionally large—three times the size of The Stomach. Body temperature is variable; in a perching bird, it drops from 40–43°C to 35–38°C, and during nighttime drops in temperature, it falls as low as 10–15°C. In this state, the birds enter torpor.

They inhabit forests and large shrubs. They feed on floral nectar, small insects, and spiders found within flowers. Unlike the nectarivorous birds of the Eastern Hemisphere, when feeding they do not perch on the plant; instead, they remain airborne, operating their wings in a highly unique manner and hovering in a single spot. In most species, the bill is long and often slightly curved, adapted for sucking nectar. They nest on branches. The nest is built, and a clutch of two eggs is incubated, exclusively by the female for 14–19 days. The chicks hatch helpless and are fed by the female, who introduces nectar into their Esophagus using her long bill. Many hummingbird species pollinate plants by transferring pollen that adheres to their heads. The total number of species is approximately 300. They are distributed throughout North and South America; along the western coast of the latter, their range extends northward to southern Alaska. Vagrant rufous hummingbirds (Selasphorus rufus) have occasionally been recorded in Chukotka.