Bird – Reproduction Study Guide


Reproduction of birds is a key process through which birds create new individuals, perpetuate the species, and transmit their genes. Birds’ reproduction is not similar to other animals in a lot of aspects. Their anatomy itself is different where most males do not have external genital organs, and females reproduce with just a single ovary (usually the left ovary). The other aspects of aves reproduction include an increase in the size of sexual organs, hormone production, and other ethological parts like how birds mate, territorial behavior, and their exhibition of pairs.

Do Birds Reproduce Sexually or Asexually?

Are birds asexual? Asexual reproduction is not yet known in avian species, but a single bird can become reproductively active and lay an unfertilized egg in its lifetime as a captive. Birds reproducing an offspring starts by laying eggs.

Bird sexual reproduction

  • The process of how a bird gets pregnant begins with a bird finding its pair to mate.

  • A male bird generally presents signals like songs and calls to attract a female bird.

  • After a pair forms, it is the end of the courtship period and the copulation period.

  • Both male and female birds have a cloaca, the single exit and entry point for eggs, sperms, and waste matter.

  • The ways birds mate and their position while having sex vary from one species to another. But in most cases, the male bird balances on top of the female bird to copulate, and both males and females face in the same direction.

  • Then the female bird moves aside her tail to expose her cloaca, and the male will curl or arch his body to rub his cloaca against the female’s cloaca.

  • The rubbing (also known as cloacal kiss) lasts for less than one second, and the sperm is quickly transferred, and the mating is completed.

  • The sperm then travels through the oviduct and reaches the infundibulum, fertilizing the egg.

  • The hard-shelled egg develops inside the female bird.

  • The eggs are then incubated by the bird that provides heat to the eggs with the help of its brood patch. Incubation can be done by both male and female birds.

  • The incubation period can last from 10 to 80 days, depending on the species.

  • After the embryo has fully developed inside the egg, hatching occurs where the beak breaks the eggshell of the baby bird.

Reproduction in BirdsSource

Courtship in Birds

The courtship period in birds can last much longer than actual copulation. Birds try to charm their partner in many ways and signals, visual and auditory. In the courtship period, the male bird tries to showcase his strength and health to female birds to convince them that they are the best mate.

The courtship period can have many stages, which begin with claiming territory to wooing a prospective mate. Some of the signals and acts performed by birds to woo a partner are:

  • Intricate songs and calls.

  • Vibration of feathers

  • Drummings displays

  • Air sacks and spectacular flights.

  • Extravagant crests.

  • Dances

  • Aerobic flights.

  • Moving wings and tails.

  • Offering nests or nests sites and food.

Courtship in BirdsSource

Establishing Territory

Once birds form pairs, most of the species establish a territory where the bird defends against other species. The territory is chosen to protect from predators and with sufficient food resources. The birds build their nest and raise their young in this territory.

  • The size of the territory depends on the birds’ species, their size, and their needs. For instance, raptors need large territories, and passerines build small territories.

  • The pair forms a small territory around the nest. In some birds like seabirds form large colonies. The incubating bird defends the nest while the other partner looks for food.

  • In most species, the territory is defended by the male though there are some species where females also defend the territory.


  • Birds reproduce sexually where males and females go through a period of courtship and then copulation.

  • The transfer of sperm to the ova happens through the cloaca, which is present in both males and females.

  • In general, birds are monogamous, and both parents take care of their offspring together.


1. How do birds reproduce sexually?

During mating, the male bird goes on top of the female, facing the same direction. They have an entrance called cloaca which they rub against each other. From the cloaca, the male sperm passes onto the female ova, where it is fertilized. After fertilization, the egg comes out of the female cloaca.

2. Do birds have penises?

Most male birds do not possess a penis apart from some waterfowl like swans, ducks, ostriches, and geese. The embryo does develop a penis, but it disappears once the egg hatches. The gene called Bmp4 is responsible for the missing penises in birds. Due to this gene, the cells at the tip of the penises of birds die faster than they grow back.

3. How often does a bird reproduce?

In general, birds nest once a year but certain species such as American Robin can nest four or five times in a single breeding season.

4. How long is a bird pregnant before laying eggs?

The incubation period in birds varies hugely from species to species. The egg may be laid within a few days or take several months before eggs are ready to be laid.

5. Do birds reuse nests?

No matter how clean their nests are, most birds do not reuse their nests. A bird builds a new nest for each clutch in a new location, and building a new nest reduces parasites and lice that lay eggs in the nest materials.

6. Do birds lay unfertilized eggs?

Apart from domesticated chickens and other pet birds, none of the wild birds lay unfertilized eggs. The eggs laid by domesticated birds are infertile and do not hatch.

7. How long is the mating season for birds?

Most of the residential species of birds start mating in spring so that the breeding season falls between mid-June and September. They prefer this period for breeding so that their young ones are not exposed to too hot or cold climates.

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  1. Bird Reproduction. Accessed 3 Dec, 2021.

  2. How Do Birds Mate?. Accessed 3 Dec, 2021.

  3. Bird Reproduction. Accessed 3 Dec, 2021.

  4. Bird Reproduction. Accessed 3 Dec, 2021.


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