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Birds are warm‑bloodedhomeothermywarm‑blooded vertebrates. They maintain a relatively constant body temperature, largely independent of the temperature of the surrounding environment. The high body temperature of the birds (41‑42°C) is the result of:

• a high rate of cell metabolism; to maintain this rate, birds eat large amounts of food and use large amounts of oxygen as well as convert a large part of the energy contained in food into heat;

• the presence of adipose tissue and feathers, which protect against heat loss;

• the ability of cooling down the body by evaporating water (panting) and behaving in a way which prevents overheating and chilling of the organism.

Thanks to the development of homeothermy, the birds were able to live in all types of ecosystems on all continents. Some of them, like penguins and petrels, inhabit even the Antarctic coastline.

Birds’ adaptations for flight

The most characteristic feature of birds are wings. The wings are covered with feathersfeathersfeathers, which give them a streamlined (aerodynamic) shape and increase their surface during flight.

The birds’ feathers are divided into down feathers and pennaceous feathers (vanned feathers) – coverts, remiges and rectrices. Down feathers together with the air between them form a layer that protects the bird from cold. Coverts cover the down and hinder the exchange of heat with the environment. Remiges overgrow the feathers and form their load‑bearing surface. Similarly to remiges, rectrices are arranged on the tail in a fan‑like fashion on the tail and are used to control the flight, maintain the balance and slow down the speed during landing.

Pennaceous feathers are composed of a shaft and a vane. The part of the shaft in the skin is the calamuscalamuscalamus; the remaining part, covered with a vane is the rachisrachisrachis. The vanevanevane is made up of barbs from which barbules equipped with hooklets go sideways. Hooklets overlap to form a light, compact and flexible surface of the vane.

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lustracja przedstawia w pionie pięć typów piór ptaka, różniących się budową. Od lewej sterówka. Składa się z dutki u dołu, stosiny wzdłuż i beżowo – brązowej chorągiewki. Chorągiewka ma taką sama szerokość po obu stronach stosiny. Następne pióro to lotka. Części pióra te same, ale chorągiewka jest węższa po jednej, a szersza po drugiej stronie stosiny. Obok powiększenie fragmentu stosiny i chorągiewki. Od walcowatej stosiny odchodzą grube promienie, od nich cienkie promyki z haczykami. Taka konstrukcja zapewnia trwałość chorągiewki. Kolejne dwa pióra: szaro – czarne i beżowe to pióra pokrywowe. Ostatnie w rzędzie jest pióro puchowe, które na dutce ma nitkowate promienie.

In order to the ability to fly, the birds must be light. Therefore their bones are pneumatisedpneumatised bonespneumatised – have spaces filled with air inside. The forelimbs of birds are in the form of feather‑covered wings. In order to the ability to fly, the birds need strong muscles to move their wings. They are attached to a wide keel on the sternum. The skull of the bird has no teeth which would burden the head during the flight.

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Ilustracja przedstawia szarego gołębia z uniesionymi skrzydłami. Głowa w lewo, na niej pomarańczowe oko i krótki dziób z otworem nosowym pod jaśniejszą skórą. Szyja krótka, mieni się kolorami piór pokrywowych. Po tułowiem czerwone kończyny tylne, pokryte łuskami, z pazurami na końcach czterech palców. W ogonie sterówki, w skrzydle lotki . Podpisy: głowa, oko, otwór nosowy, dziób, szyja, pióra pokrywowe, tułów, łuski, pazury, kończyna tylna, sterówki, ogon, lotki, skrzydło

Respiration

In birds, gas exchange takes place in lungs made up of a large number of thin tubes intertwined with each other. As a result, they have a large gas exchange surface. This is important because flying requires a great deal of energy, which is released in the presence of oxygen. Air is stored in air sacsair sacsair sacs. These are thick‑walled tanks filled with air and connected to the bronchi. They reduce the specific weight of the bird.

Lung ventilation can occur in two ways. During walking or resting, the air is pumped into the lungs thanks to the rhythmic movement of the chest, caused by the contraction of the intercostal muscles. During the flight, the chest is stiffened, as it provides support for the muscles moving the wings. When the bird raises its wings, the inhale takes place and the air enters the lungs and the air sacs through the airways. When the wings are lowered, the exhale takes place. Then the used air escapes from the lungs and the air stored in the air sacs is sucked into the lungs, oxygenating the blood. This mechanism is called double respirationdouble respirationdouble respiration, because oxygen‑rich air flows through the lungs of the bird twice, both when it is inhaled and when it is exhaled.

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Ilustracja przedstawia schematycznie dwubocznie symetryczny układ oddechowy ptaka. Ciemnoróżowa tchawica prowadzi do płuc w tym samym kolorze. Z płuc wyrastają w różnych kierunkach błękitne pęcherze, czyli worki powietrzne. Po obu stronach narysowano bladoróżowe kości ramieniowe, do których wrastają pęcherze powietrzne. Podpisano: tchawica, płuco, worek powietrzny, kość ramieniowa

Birds’ reproduction

Birds, like reptiles, are amniotes. The embryo of the bird develops from an embryonic disc which forms on the surface of the yolk constituting the source of food for the embryo. The egg yolk is kept in place by the protein structures known as strands. The highly hydrated protein protects the germ from drying out and absorbs shocks. The pores in the egg shell and the air chamberair chamberair chamber allow for gas exchange. The parchment membranes and the calcareous shell protect the egg from mechanical damages. As the embryo develops, the shell becomes thinner, as the calcium it contains is gradually built into the bone.

Bird nestlings are usually altricial species that hatch out unfledged, blind and dependent on their parents for a long time. If the nestling after hatching is covered with down feathers and has open eyes, can immediately leave the nest and follow its mother, it is called precocial species. This is the case in hens, ducks, ostriches.

Chaffinch occurs in agricultural and urbanized areas. It inhabits all types of forests, parks, cemeteries and even house gardens and parcels. It feeds on seeds of herbaceous plants, trees and shrubs, as well as fruits and grains and sometimes tree buds. It can also eat insects and arachnids from tree branches.

Eurasian eagle‑owl is the largest Polish owl. It hunts at night, guided by its hearing and eyesight. Feathers around the eyes and the beak create a facial disc, an antenna that concentrates sounds and guides them to the ear. Eurasian eagle‑owl has a massive silhouette, a large round head, orange eyes and characteristic clusters of feathers resembling ears. It inhabits vast primary forest areas. It hunts for medium sized birds and mammals, sometimes also insects.

The fastest bird is the peregrine falcon, which can reach speeds of up to 300 km/h when nose‑diving down. It is characterized by a large, bulky and strong silhouette with long, sharp‑ended wings and a massive head. It hunts for small vertebrates during the day, mainly birds and mammals. It inhabits all continents, most often river valleys, mountain areas and forests close to water reservoirs. It can also be found in urban areas.

Conclusion

• Birds are warm‑blooded vertebrates that can fly (or, as in the case of ostriches, their ancestors could) and inhabit all the world's ecosystems.

• The birds' adaptations to flight include, among others, covering with feathers, a forelimb transformed into a wing, the presence of a keel on sternum, a light skeleton, and the presence of air sacs.

• The shape of the bird's beak depends on the type of food it feeds and how it is obtained.

• The structure of the bird's hindlimbs depends on the bird's lifestyle and the inhabited environment.

• Double respiration in birds is due to the presence of air sacs.

• Birds are oviparous, characterised by internal fertilisation.

• Birds are amniotes, their young develop in eggs and are surrounded by foetal membranes which provide optimal conditions for their development.

Keywords

birds, pneumatised bones, double respiration

Glossary