Reproduction in birds

The formation of couples

In temperate zones, the breeding period takes place in spring. The mating is preceded by a set of special events: the courtship.

The male, adorned with a new plumage, often special (wedding plumage), seeks to captivate the female by the display of his finery, dances, fights with other males and, most often, by his song whose qualities are developed at this time. Often, the male also makes small gifts to his beautiful. When the couple is constituted, it can last until the end of the summer, but rarely beyond.

The reproductive system

In the female, the ovary appears as a cluster of reproductive cells that mature successively. The mature egg is collected by a large pinna and descends into the tube, or oviduct, where it can be fertilized.

In the male, the mating organ, or penis, is absent except in exceptional cases. In the majority of cases, during mating, the spermatozoa arrive in the male's cloaca through the vas deferens and are released into the female's cloaca. They then go up into the oviduct to meet the egg. Fertilization is thus internal. 

The couple will then look for a hidden or inaccessible place where the female can lay her eggs. Most birds build a nest on a branch fork in a tree or shrub, but some lay their eggs in a hole in a tree (Chickadee), in a building wall or under a roof (House Sparrow, Black Swift). Finally the swallows elaborate cups in mud under a ceiling or a windowsill.

The laying of eggs
 

Many birds lay eggs only once a year but some species lay several times a year, as soon as the young are raised (2 clutches in most of the Chickadees and the Redstart, up to 3 clutches in the Blackbird).

The eggs are laid in the morning, and are laid at least one day apart. In order for all the eggs to hatch at the same time, the female does not begin incubation until all the eggs have been laid. Only raptors start incubating from the first egg, the chicks will not be the same age, the youngest will die first if there is not enough food.

Brooding

The eggs must remain most of the time at a constant temperature close to the bird's body temperature. The incubating adult turns them regularly to distribute the heat inside. The ventral part of its body, which covers the eggs, loses its feathers to guarantee the transmission of a maximum of heat. This incubation period starts only when all the eggs are laid. Its duration varies in the small birds between 10 and 15 days (13 or 14 days in the titmouse and in the thrushes).

The brooding is practiced either by the female alone, or alternately by the male and the female and sometimes by the male alone. While the female broods, the male brings her food and often the charm of his song.
 

Feeding of the young

There are two kinds of behavior of the young after hatching:
 

• Nesting species whose young are born with down and can leave the nest and feed on their own as soon as they hatch, such as the Meadow Quail.

• Nesting species whose chicks are born naked and blind and are dependent on their parents for some time. The parents then do not cease to feed them. For example, in the great tit, the feeding time is 17 hours per day during which the parents bring 30 to 50 insects per hour to their young. These pass from a weight of birth of approximately 1,3 grams to that of 18 grams in less than 15 days.