How Do Birds Mate?

Quick answer: Most birds mate by pressing their cloacae together in a quick “cloacal kiss,” which transfers sperm. Before this, birds often court with songs, dances, or gifts, and most species lay eggs after mating.

Most birds mate with a very quick “cloacal kiss”: the male balances on the female’s back and the two press their cloacas together for a second or two so sperm can pass from male to female. Only about 3% of bird species, such as ducks, geese and ostriches, have a phallus. Before mating, many birds put on amazing courtship displays to win a partner.

Courtship: Winning a Mate

Birds are famous for their spectacular courtship displays. A pair of birds may spend days or weeks courting, even though the mating itself lasts only seconds. Courtship helps birds recognize members of their own species, and it lets females choose a healthy, strong mate who will help them raise chicks with the best chance of survival.

Charles Darwin was fascinated by bird courtship. Watching it helped him develop his ideas about how females choosing mates can shape the way a species looks and behaves over many generations.

Most bird courtship involves some mix of song, dance and showy feathers.

Songs

Males of many bird species sing to attract a female and warn other males to stay out of their territory. Rival males may try to outsing each other, and scientists think this competition helped make some bird songs so long and complex.

Dances and Flying Displays

Male birds-of-paradise from New Guinea hop, bow and spread their incredible feathers to show off to females. Some falcons perform high-speed chases and dives in the sky, and male hummingbirds zoom up high and swoop down in steep dives right in front of a female.

The male lyrebird of Australia clears a small mound of earth to use as a stage. There he sings, copies the calls of other birds and throws his long, lacy tail feathers over his head while he dances.

Feathers and Decorations

The peacock’s huge, shimmering tail is one of the best-known examples of feathers that evolved mainly to attract a mate. He spreads it into a fan and shakes it to make the eyespots shimmer.

The male bowerbird builds a structure called a bower out of sticks and decorates it with carefully chosen objects such as flowers, berries, shells, stones and even bits of colored plastic. Females visit several bowers before choosing a mate.

Bird Anatomy: The Cloaca

Most birds do not have external reproductive organs. Instead, both males and females have a single opening under the tail called the cloaca (say klo-AY-ka), from a Latin word meaning “sewer.” The cloaca is used for getting rid of waste, for mating and, in females, for laying eggs. It is usually hidden by feathers.

Birds are not the only animals with a cloaca. It is also found in reptiles, amphibians and elasmobranch fish such as sharks and rays.

From the outside, the cloacas of male and female birds look almost the same. During the mating season, the cloaca swells, and males store sperm in small swellings near the cloaca, ready for mating.

How Do Birds Mate?

Mating in birds works quite differently from mating in mammals. Here is what usually happens:

• The female crouches and moves her tail to one side to show she is ready.
• The male hops onto her back, balancing carefully, often flapping his wings to stay steady.
• He curves his tail down under hers so their cloacas touch.
• In that brief “cloacal kiss,” sperm passes from the male into the female.

The whole thing is usually over in a second or two. Because only some of the sperm reaches the eggs, a pair often mates many times during the breeding season to make sure the eggs are fertilized. The female can also store sperm inside her body for days or even weeks.

Birds With a Phallus

About 97% of bird species have no phallus at all. The other 3% include ducks, geese and swans, along with ostriches, emus and some other flightless birds, and the ground-dwelling tinamous of Central and South America.

In these birds, the phallus is filled by lymph fluid rather than blood, and it is only used for a very short time during mating. Many of these birds mate on water or on the ground.

Why did most birds lose this organ? Scientists are still studying the question. One old idea was that it made flying harder, but that does not explain why ducks, swans and geese fly long distances on migration. Research on chicken embryos shows that the organ starts to grow and then stops early in development, but the reason for this evolutionary change is still a mystery.

From Mating to Eggs

Birds do not have a pregnancy like mammals. Soon after mating, a fertilized egg begins its trip through the female’s body, where the white, shell membranes and shell are added. This takes about a day in many birds, so females of many species lay one egg a day until the clutch is complete.

At first, the embryo inside is just a tiny cluster of cells. It develops into a chick only after the egg is laid and kept warm by a parent sitting on it. The incubation period ranges from under two weeks in many small songbirds to around two months in some large seabirds.

What to Do If You See Birds Mating

If you spot birds courting or mating, enjoy watching from a distance. Getting too close may scare them away, interrupt their courtship or even cause them to leave a good territory for a worse one.

Once a pair starts nesting, you may get the chance to watch a bird family grow. Use binoculars, keep your distance from the nest and never touch the eggs or chicks. That way the parents can raise their young in peace.