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Bird Reproduction

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Is this pair of birds actually a "couple"?

Yes. Birds do actually pair up each mating season, if not for life. And the male better be prepared to treat his female properly. There is actually an elaborate process in which the female chooses her mate.

Bird Reproduction

Reproduction in birds may be quite complicated and lengthy. Birds reproduce sexually and have separate sexes and internal fertilization, so males and females must mate for fertilization to occur. Mating is generally preceded by courtship. In most species, parents also take care of their eggs and hatchlings.

Courtship and Mating

Courtship is behavior that is intended to attract a mate. It may involve singing specific courtship songs or putting on some type of visual display. For example, a bird may spread out and display its tail feathers or do a ritualized mating “dance.” Typically, males perform the courtship behavior, and females choose a mate from among competing males.

During mating, a male bird presses his cloaca against his mate’s cloaca and passes sperm from his cloaca to hers. After fertilization, eggs pass out of the female’s body, exiting through the opening in the cloaca.

Nesting and Incubation

Eggs are usually laid in a nest. The nest may be little more than a small depression in the ground, or it may be very elaborate, like the weaver bird nest in Figure below . Eggs that are laid on the ground may be camouflaged to look like their surroundings (also shown in Figure below ). Otherwise, eggs are usually white or pastel colors such as pale blue or pink.

Variation in Bird Nests. A weaver bird uses grasses to weave an elaborate nest (left). The eggs of a ground-nesting gull are camouflaged to blend in with the nesting materials (right).

After birds lay their eggs, they generally keep the eggs warm with their body heat while the embryos inside continue to develop. This is called incubation, or brooding . In most species, parents stay together for at least the length of the breeding season. In some species, they stay together for life. By staying together, the males as well as females can incubate the eggs and later care for the hatchlings . Birds are the only nonhuman vertebrates with this level of male parental involvement.

Hatchlings

Image copyright Vishnevskiy Vasily, 2011

Ground-nesting birds, such as ducks and chickens, have hatchlings that are able to run around and feed themselves almost as soon as they break through the eggshell. Being on the ground makes them vulnerable to predators, so they need to be relatively mature when they hatch in order to escape. In contrast, birds that nest off the ground—in trees, bushes, or buildings—have hatchlings that are naked and helpless. The parents must protect and feed the immature offspring for weeks or even months. However, this gives the offspring more time to learn from the parents before they leave the nest and go out on their own.

Summary

  • Birds reproduce sexually and have internal fertilization.
  • Mating is generally preceded by courtship.
  • Birds' amniotic eggs have hard shells and are laid in a nest. The eggs are usually incubated until they hatch.
  • Most species have a relatively long period of parental care.

Review

1. What is courtship? What is its purpose?

2. Contrast hatchling maturity in birds that are ground-nesting and those that nest off the ground. What is the adaptive significance of the differences?

Practice

Use these resources to answer the questions that follow.

  1. How does bird reproduction begin?
  2. Does a bird egg have to be fertilized?
  3. Describe the fertilization process in birds.
  1. Why do male birds need an extravagant display?
  2. Describe how some male birds put themselves on display.

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