How Are Birds’ Eggs Fertilized? Everything You Should Know!


Written by

Clinton Atkins



George Dukes

how are birds' eggs fertilized

Birds are well-known as egg-laying species, but do you know the answer to, “How are birds’ eggs fertilized?

Like mammals, bird reproduction begins when an egg (or ovum) comes into contact with sperm and is fertilized. Once fertilized, the ovum becomes the nucleus of the egg, which consists of the yolk and a protective outer shell.

However, domesticated birds, such as chickens and ducks, can lay eggs without sperm. Those are the eggs you usually buy in stores or supermarkets.

Typical Mating Behavior and Alternative Reproductive Strategies


Because the structure of most birds does not serve as a spermatic tube, their reproductive behavior is different from that of mammals and reptiles.

While the mating action of mammals and reptiles takes place over a long period of time, this act in birds is short-lived. However, while mammals and reptiles need a break between mating sessions, birds can mate several times a day.

Most birds have lost their internal organs during evolution, but about 3% of the males of the living species still have developed penises. Examples include swans, ostriches, ducks, and geese. The rest of the birds, such as eagles, penguins, or seagulls, do not have penises. Chickens can also have, but they are all small and short tubes so they can’t get in. In that case, what would they do?

At this point, the male’s semen will become a “cloacal kiss”. The mating position and posture of birds can vary from species to species, but it is most common for males to balance on top of females. At this point, both will face the same side and the female will move her tail to the side so that the male can easily rub against the cloaca.

Bird Egg Development

Birds have two ovaries since they are embryos. With the exception of the Australian brown kiwi and a few raptors, adult birds usually develop only the left ovary, with the right ovary regressing.

An ovum, or egg, from a follicle developing on the surface of an ovary breaks off and enters the end of a fallopian tube (like a woman’s fallopian tube). When these cells enter the fallopian tube, the yolk sac, the “nutrient” source for the developing embryo, is covered with a coating.

Then, the ovum inside the yolk will be covered with an albumen layer, which we often call the egg white, followed by a thin membrane, and finally the hard outer shell. The hard shell contains calcium and minerals that are added while the egg is in the uterus, before it enters the cloaca and exits the bird’s body.

Cloaca is the only posterior opening for the digestive, reproductive, and urinary organs of birds. It is located under the tail and is covered with fur on the lower abdomen. Birds pass eggs out of the body through this opening vent.

In order for the eggs to be pushed out easily, their sharper end should face the vent. If the eggs are not in this position or the eggs are oversized, the bird may have difficulty laying eggs and may require veterinarian intervention. In particular, parrots take two to three days for eggs to travel from the ovary to the fallopian tube and out the vent.

Egg Fertilization Process


Do birds have internal or external fertilization? What happens to a fertilized bird egg? Before being ejected, the egg is fertilized inside, so an egg that has already been laid cannot be fertilized anymore. Bird egg fertilization process takes place very early in the fallopian tube, before the egg white and yolk cover the ovum, that is, while the cells of the ovum are dividing.

Fertilization occurs when a male and female mate with each other before the ovum is released into the fallopian tube. The male sperm can survive in the fallopian tube for a few days to meet the egg of the female.

In the case of sperm in the fallopian tube at the time of division of the ovum, the sperm will penetrate into the ovum immediately to fertilize the egg. The sperm then travels through the rest of the fallopian tube.

At a glance, there is no obvious difference between an unfertilized egg and a fertilized egg. When the female incubates the eggs in her nest and we see the chicks being born, we know the egg has been fertilized from the inside.

Artificial Insemination

In some special cases, there can be reluctant mating between birds and this can cause unwanted problems for the farmer. Veterinarians can intervene by artificial insemination. They will collect sperm and transfer it into the cloaca of the female. This process is highly specialized, so farmers should not try to do it themselves.

Verification of Fertilization

As mentioned above, although it is difficult to tell if an egg is fertilized or not with the naked eye, we still have a way to know. You can check if an egg has been fertilized by placing the egg under a bright light and looking for blood vessels that are present for the life of an embryo.

Occasionally, the embryo may be a shadow or small black dot. You should be using lights that give off less heat to avoid affecting the growth of young birds.

Note: Many bird lovers find it interesting to observe the unique behaviors of birds. However, if you see them mating, it is best to keep your distance because getting too close can frighten them and make them leave. This can hurt their relationship.


Are bird eggs fertilized before or after they are laid? Now you have the answer! Whenever a bird is ready to mate, its reproductive parts, the testes and ovaries, expand and generate sperm and eggs.

Male birds keep sperm in their cloaca until the partner is available, and females accept that material in their cloaca before it goes further into their body to fertilize their eggs and initiate egg development.

I hope you find this post on how are birds’ eggs fertilized useful and interesting. If you have any questions or more information about bird egg fertilization, don’t hesitate to leave us a comment!

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