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Biologia del falciot negre



The common swift (Apus apus) is a member of the Apodidae family, with 92 species that are distributed throughout the world, though most are tropical. They spend nine month in Africa, arriving for the breeding season to the south of Europe in April. Common swifts reach more northern latitudes in the first and second week of May. There are other three species that breed in Europe, although in the southern Mediterranean area; pallid swift (Apus pallidus), alpine swift (Apus melba) and white-rumped swift (Apus caffer).

Common swifts are long-lived birds that spend almost their entire life on the air, gathering their food and material for nesting in flight. They drink by skimming over the surface of still water. They do not show evident sexually dimorphic characters, they mate both in flight and on the nest, and may even pass the nights without roosting. Swifts are altricial birds, which do not exhibit post-fledging care and breed once per season.

They have long wings, with a body shape adapted to rapid and efficient flight. Swifts with a wing span of 40 cm need the ability to brake suddenly and fold their wings before entering nest holes of less than 8 cm. Swifts never foot on the ground except by accident, this aerial life limit their choice of nesting sites to places above the ground with a clear drop to allow a fast take off. Even though their long wings and short legs, they can take off from flat surfaces. They have characteristic sticky saliva used for building nest. They salivary glands are greatly enlarged in the breeding season. Swift saliva have an essential function in shaping and lubricating the food balls that they give to the young, also transferring beneficial flora to the chicks and establishing their immune competence in the first days.

Swifts are dependent on food captured in the air, being abundance or scarcity of insects important in the breeding success. Warm temperature, sunny and little rain conditions (fine weather), increases insect abundance and it is favourable to this success. Cold, rainy or windy weather conditions (poor weather) are detrimental as they encounter great difficulties in finding enough food as insects are scarce.


Normally swifts pairs previous years’ mate, although they arrive in different days. Even the two members do not arrive together, they rejoin because return to the same nest of previous years. This may suggests that pairs are separated out of the breeding season. It has been recorded from on data from a colony controlled for longer than 20 years, pairs being together longer than 10 years.

Some authors denoted that swifts breed in their second year; however others observed that pairs did not breed successfully before third or four years of age.


Eggs are white, like those of other hole-nesting birds. Swifts usually lay two or three eggs, with remarkably differences depending of the latitudes related to the average number of young that parents can rise. The most frequent incubation period is 20 days, laid with some degree of asynchrony, from two to three days.

Both parents share incubation. It has been observed that eggs and hatched naked chicks can be left unattended in cold conditions for long periods meanwhile both parents are out collecting food. Swifts are the only birds that nest in cool regions which can leave eggs unincubated and young unattended for long periods without harm. Although the cold temperature, it has been denoted that eggs hatch normally. The ability of the developing embryo to cool for some hours have an important advantage for an species breeding in areas of unpredictable summers, although this ability is unusual among birds.

Swifts as altricial species are blind, naked and helpless at hatching. Parents care for the chicks until they fledge.By the second week after hatching, both parents are much of the time on hunting, leaving the nestlings unattended. Nestlings have a particular thermoregulation and usually from four days old they may not be warmed by their parents even during the night, despite the temperature, assuming also certain effect of mutual warming between siblings.

In almost all latitudes it is described an average nestling period of 42.5 days, being 37 days in fine weather and the longest 56 days in poor weather, suggesting that poor weather may considerably prolong the nestling period.

Many authors sustain that swifts have particular adaptations related to the scarcity of food, the so-called facultative lethargy. Swift nestlings have evolved to revert their metabolism to a cold-blooded condition, using their fat stores for vital functions. Other birds are known to have these facultative hypothermic responses, for example the common poorwill (Phalaenoptilus nuttallii) during hibernation and many hummingbirds’ species during cold nights. One researcher, Koskimies, conducted physiological studies related to this adaptation to the poor weather and concluded with several affirmations: a swift chick is able to survive up to 12 days without being fed, being same capacity in adults much lower; the fat accumulated along nesting period is used for vital functions being able to use more than 50% of its body weight along the fasting period; the feathers continue growing along this fasting period and finally that the chick can enter a torpor status with its metabolism decreased to environment temperature and its fluctuations. It has been recorded that nestling temperature may drop to 21ºC at night (41ºC normal adult temperature), and recover it during the day even without food. ALso recorded in extremely unfavourable years, adult swifts in hypothermia state during the night, which seems to reduce the energy loss and increase survival in years of extreme food scarcity.




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Ultrich Tigges, expert reconegut, ha creat un lloc on els recursos són quasi il.limitats!