There are different bird classifications,which are put various signs. One of them is the degree of development of newborn chicks and the features of their further growth. According to this criterion of systematization, two large groups stand out: brood birds, examples of which will be given in our article, and nesting. Let us consider them in more detail.
All representatives of this class multiply,laying eggs, after hatching them. After a certain time, the chicks hatch from the eggs. Breeding birds are characterized by the fact that their newborn chicks are almost immediately ready for independent life. The body of the nestlings is completely covered with down. It warms and protects the young organism from unfavorable environmental conditions, and especially from sharp daily temperature changes. This allows such birds to immediately leave the nest and not freeze.
Eggs from which appear brood birds,are quite large in size and contain a large supply of valuable nutrients. The embryo uses them in order to reach a considerable degree of development in the shell and move to an independent life almost immediately after hatching. The females have to incubate eggs for a long time - sometimes more than three weeks. Immediately after hatching chicks are able to see and hear well. Their muscular system is fully functioning, which means that they move independently. This is extremely important for protection from unexpected predators. After a few hours, the kids already know how to run fast and fly a little. And after a couple of weeks can independently find food.
Nesting birds hatch absolutelyhelpless chicks. They are born with bare skin, plumage, sight and hearing are absent. Examples of nesting birds are sparrows, woodpeckers, cuckoos, pigeons, etc. After birth, they can not keep on their feet, thermoregulation is not yet formed. For these reasons, these chicks stay in the nest for a certain time, needing the care of their parents who feed and heat them.
There is also an intermediate group, representativeswhich combines the features of both nesting and breeding birds. For example, owl chicks appear blind and develop under the supervision of their parents, but are completely covered with plumage. But gulls for a long time remain in the nests, despite the fact that they hatch and sighted and pubescent.
Breeding birds, whose representativessufficiently diverse, are waterfowl or live on land. They do not build their nests high on the trees. They are distinguished by their large body size and large mass. Therefore, chickens can at first slightly flutter, gradually completely feathering. Waterfowl brooders first have weakly developed wings, most of the time devoting to the formation of swimming skills.
And now let's take a closer look at the main groups of this group.
Breeding birds include all species of the orderthe cranes. They are characterized by a long neck and the same beak and legs. Thanks to the presence of loops in the trachea, they emit characteristic sounds resembling a pipe. Being brood, the cranes build nests right on the ground. These are fairly large birds, up to a meter and a half. The span of their wings can reach two meters. The most common species of this order are the gray, steppe and crowned cranes.
Waterfowl brood birds (examples are swan,duck and mallard) belong to the group of geese. Their characteristic feature is the presence of a wide and flattened beak. Inside its upper part there are horny plates, which serve to filter out food particles from water.
The saying "go out dry" existsthanks to an anseriform bird. It's all about having a coccygeal gland, the secret of which they lubricate their plumage. As a result, it becomes waterproof. Ants are an important object of the fishery, because they have tasty, nutritious meat and fat, which has medicinal properties. It should be said about warm feathers and down that are used for filling blankets and pillows, as well as getting knitted products.
Thus, brood birds are more viable than nest birds and are of great economic importance for humans.