About us: We own the Wild Birds Unlimited nature shop in East Lansing, Michigan,
a store that provides a wide variety of supplies to help you enjoy the birdwatching hobby.

This blog was created to answer frequently asked questions & to share nature stories and photographs.
To contribute, email me at bloubird@gmail.com.

Wednesday, February 16, 2011

How Do Birds Lay Eggs?

Bird courtship is generally the male’s responsibility and usually entails singing but can also consist of many other activities like drumming or dancing.

During breeding season, the male's testes which lie within their body at the end of each kidney become several hundred times larger than normal to produce sperm which moves to the cloaca where it is stored until insemination (the act of sex). In bird anatomy, a cloaca is the posterior opening that serves as the only opening from which they excrete both urine and feces, unlike mammals, which possess two separate orifices for evacuation.

The female bird's ovaries are also enlarged during breeding season to produce the ovum. The ovum is a single cell that we recognize as the yolk of an egg. The female bird unfans her tail, moves it to one side while the male climbs up onto her back or gets close to her. Their cloacas are pressed together and the sperm moves from the male to the female. This act is called a cloacal kiss.

The ovum is fertilized in the female bird's oviduct by a sperm cell from the male bird. The oviduct is a tube that transports the egg from the ovary to the cloaca and where the white of the egg and shell are formed. In most birds, the ovary releases an ovum at daily intervals during the breeding season until a complete clutch of eggs is laid. Once fertilized, the ovum becomes the nucleus of the egg. The egg will be laid by the female into her nest, incubated, and then the baby bird will hatch.

Sperm is stored by the female for at least a week, in some species over a hundred days. Then as each ovum from the ovary moves into the oviduct, it gets fertilized with the stored sperm, producing a clutch of eggs, all with the sperm from that one cloacal kiss.

There are a few species of birds where the males do possess a retractable penis that can be pulled back into the bird. These birds include ostriches, cassowaries, kiwis, swans, geese, and ducks. Since waterfowl sometimes make love while in the lake or pond, the penis helps ensure that the sperm is not washed away by the water.

And, although it is not necessary to copulate frequently since the sperm is stored within the female, remember those hormones are still making the birds excited. Many pairs of birds will mate numerous times within a few days.