Apus apus

The swift or common swift (Apus apus) is a species of apodiform bird in the family Apodidae typical of Eurasia and Africa.

Description

The Common Swift is a bird specially adapted for flight, with sickle wings, a short shallow forked tail, a very wide and large mouth topped with a small bill, very short legs with no opposable thumb, and small but extraordinarily prey claws. strong that allow it to cling to vertical surfaces. Its plumage is blackish with a small whitish or light gray patch on the throat, only visible at close range. The Common Swift has a body length of 16–17 cm, while its wingspan is 42–48 cm, which in flight gives its wings their characteristic broad crescent silhouette.

Taxonomy and etymology

The Common Swift was scientifically described by Carlos Linnaeus in 1758 in the tenth edition of his work Systema naturae, under the name Hirundo apus, which means "swallow no feet". In 1777 it was transferred as type species to the genus Apus by Giovanni Antonio Scopoli. Two subspecies are recognized:

• Apus apus - extends across Europe, North Africa and West Asia, reaching Lake Baikal, passes the inverno in southern Africa.
• Apus apus pekinensis - occupies Asia from Iran to Mongolia and China, spends winter in East Africa.

The etymology of its scientific name, Apus apus, comes from ancient Greek, where apous (άπους) means "without feet", in reference to its aerial habits. Its Spanish name "swift" comes from the corruption of its old name oncejo, due to confusion with the word "swift" which means "ligature, lasso". In turn, elevenjo came from sickle, alluding to the shape of its silhouette in flight.

Behavior

The victors spend most of the year flying without posing.

Since the very origins of zoology, what was confirmed at the end of the 1960s was suspected: that swifts spend most of their lives in the air: they eat, sleep and mate while flying. They only perch to lay eggs, incubate them and raise their chicks. They remain in uninterrupted flight for nine months a year. The young leave the nest one morning flying suddenly, without the need for prior learning, and never return to it. At night, these birds rise up to 2,000 m above sea level and sleep there, flying. During sleep, flapping is reduced from the usual ten movements per second to just seven. Due to their strange aerial habits, many things about the life of these birds are still unknown. They nest in high cliffs and vertical walls from which they resume flight. Due to their special wing morphology and their short legs, if they fall to the ground they experience great difficulty in taking flight, and they need to do so from a high place.

It is a migratory bird that in the middle of the boreal spring (austral autumn) appears throughout almost all of Europe, North Africa and Central Asia, while in the boreal winter (austral summer) it is found in southern Africa. In the field, it nests gregariously on slopes but is especially adapted to human settlements. It forms its nests under cornices and eaves of buildings and houses. It is usually faithful to its nesting place; it returns to it and they rebuild it when necessary.

Food

The Common Swift feeds on tiny flying insects, which it catches in its wide beak, which is constantly held open as it flies. It also collects on the fly the materials with which it builds the nest.

Playback

Eggs of Apus apus

Reproductive maturity is reached at two years of age. The swifts are monogamous in habit and have only one breeding period per year, in the areas of summer migration. Unlike the pale swifts, which have two clutches. During the nesting period, each breeding pair makes a single clutch of 2 to 3 eggs that oscillate between 3.2 and 4.2 grams. The incubation time is 19 to 21 days. The young leave the nest around 35 to 59 days after hatching. The juveniles leave the nest flying and permanently. The selection of the nest site depends on the availability of cavities in the walls and eaves of the roofs, as well as their distance from the ground.

The development of young nestlings is differential. The internal organs (liver, kidneys and intestines) are the first to reach their final weights. The skeletal and muscular systems follow in the process, and the flight plumage (t-shirts and rectrices) takes the longest and marks the end of the nesting period. Under good feeding and development conditions, the young swifts leave the nest with a slight overweight of 6-7 grams with respect to the adults. This reserve allows them to face the first difficulties of aerial life, since the abandonment of the nest is definitive.

Young bird, still unable to fly.

It is also interesting to note that the development of juveniles in the nest is largely related to ambient temperature. The entry of cold fronts or bad weather in the nesting areas considerably reduces the presence of flying insects. This leads to a temporary removal of the swifts towards areas of greater supply or specifically to the edges of the low pressure area. This evasive movement occurs above all in one-year-old individuals, since they have not yet nested and, therefore, they are not linked to a fixed location; but also includes nesting individuals. These movements can be hundreds of kilometers. Nestling juveniles under normal conditions can survive parental absence for four days or more, entering a torpor that reduces heart rate from 90 to 20 beats per minute and body temperature from 36-39°C to about 20°C..

Migration

Common Swifts are migratory birds. Their summer breeding range is from Portugal and Ireland in the west to China and Siberia in the east. They breed as far south as North Africa (in Morocco and Algeria), with a presence in the Middle East in Israel, Lebanon, and Syria, the Near East through Turkey, and across Europe as far north as Norway, Finland, and most of subarctic Russia. Swifts migrate to southern Africa by a variety of routes, ending up in Equatorial and Sub-equatorial Africa, excluding the Cape of Good Hope.

Subjects in a geolocator tracking study demonstrated that swifts that breed in Sweden spend the winter in the Congo region of Africa. Swifts spend 3–4 months in Africa and a similar time breeding; the rest are spent flying, returning to their nest or migrating.

The predominant direction of travel through Central Europe is from south to southwest, so the Alps and Pyrenees do not present a barrier. When the weather is bad, the swifts follow the rivers, because there they can find a better food supply. The population of western and central Europe crosses the Iberian Peninsula and the Maghreb. Swifts from Russia and South-Eastern Europe make a long journey through the eastern part of the Mediterranean. It is not clear where the two groups stand. The western group of swifts mainly follows the Atlantic coast of Africa to circumvent the Sahara and the eastern group follows the Nile River. Once they reach the savannah they converge to reach their winter feeding grounds. During the summer in Africa, there is a great abundance of insects for swifts, as the region is in the Intertropical Convergence Zone. Swifts have an almost uninterrupted presence in the sky.

During the spring some swifts, usually some of the sexually immature less than one year old, remain in Africa. Most fly north to their destinations in Europe and Asia. The birds use low pressure fronts during their spring migrations to exploit the flow of warm air from the southwest and, on the return trip, ride northeasterly winds on the back of the low pressure fronts.

Swifts return to Europe in the second half of April and first third of May, and tend to prefer to stay in lowlands and near water rather than high ground. In more northerly regions such as Scandinavia or Russia, the swifts arrive around June. The weather along the voyage has a huge influence on the date of arrival, so swifts may return to a region at different times year after year.