Do Birds Get Pregnant? | Learn How Birds Reproduce

Do Birds Get Pregnant? 

Fertilization occurs internally in birds, however, the development of the embryo occurs outside the female bird, once the egg has been laid. Pregnancy is the process of young developing in the uterus and since chicks develop inside the egg rather than in the mother’s uterus, birds do not become pregnant. 

Instead, once a fertilized egg has been laid, birds will sit on the clutch to incubate the eggs until they hatch. This article discusses the process that underlies reproduction in birds.

How Do Birds Mate and Reproduce?

How Do Birds Mate and Reproduce
Image of a Dunnock’s swelled cloaca prior to copulation
Credit: Arend Vermazeren

Do Birds Have Sex? 

Birds, like mammals, do have sex in order for the females to lay eggs. However, unlike mammals, male birds do not have a penis and female birds do not have a vagina, making the act of intercourse slightly different from what we may imagine. 

Instead of these mammalian sex organs, both male and female birds have what is known as the cloaca. As a pair of birds get ready to copulate, sex hormones cause the cloaca of both parties to swell and protrude. The birds then briefly press their cloacas together in an act sometimes called a “cloacal kiss.” 

Copulation is very short, only lasting a few seconds, but this is more than enough time for males to transfer their sperm into the female’s cloaca. 

Bird Reproductive Organs – Cloaca

Instead of a penis and a vagina, both male and female birds have a cloaca (Koh-ay-Kah). The cloaca is a single posterior opening that is linked to an internal chamber. It’s located at the rear of the bird’s body, just under the base of the tail, and is covered by feathers on the lower abdomen. 

The cloaca acts as an exit for a number of internal systems, being the reproductive, digestive, and excretory tracts. This means that gametes, eggs, feces, and urine all leave via the cloaca. The black and white color of bird excrement is therefore due to the fact waste products are excreted simultaneously. 

The black parts of bird excrement are the digestive waste whilst the white parts are the urates. In males, sperm gets discharged from the testes through the cloaca. In females, eggs are laid through the cloaca, and sperm is received into it.  

How are Bird Eggs Fertilized? 

Unlike mammals, female birds only have one ovary. The right ovary stops developing once the female hatches, but the left ovary continues to develop until the female reaches maturity. It’s thought this is to reduce the weight of birds which is beneficial for flight. 

Prior to ovulation, the follicular sac will rupture, releasing an ova into the oviduct. If copulation then takes place, sperm will be transferred into the female’s cloaca from the male and travel to the ova to fertilize it. Some female birds can store sperm for several days or even weeks before the egg is fertilized. The ova will continue its journey through the oviduct, irrespective of whether it has been fertilized or not. 

An unfertilized egg will still be laid, but no embryo will develop. These are the eggs that we consume. When it reaches the magnum, the next section of the female reproductive tract, estrogen stimulates the magnum to produce albumin (the white of the egg). Then, the egg will move into the isthmus, which is where the membrane that sits underneath the eggshell is produced. Next, the egg moves into the uterus where the eggshell is calcified. The egg will then remain in the vagina until it’s ready to be laid. 

How Long is a Bird Pregnant Before Laying Eggs?

How Long is a Bird Pregnant Before Laying Eggs
Image of a Pied Wagtail sitting on its nest with its offspring
Credit: benjamint444

Do Birds Build Their Nest Before They Get Pregnant?

Whether birds build their nests before or after they copulate depends on the species. In fact, some avian species don’t build nests at all! A lot of bird species begin building their nests after mating and fertilization have occurred. This is because nest building can be a lengthy and energy-intensive process, so it would be a waste of resources to build nests that they are not going to use. 

However, this is not true for all birds as for some species, nest building is a key part of courtship and actually finding a mate. Male bowerbirds and male weaver birds build elaborate nests in hopes of attracting a mate. Bowerbirds will go one step further and decorate their nests with twigs and brightly colored objects in an attempt to attract a female. 

Nest building is a sexually selected trait, with the quality of a nest indicating high parental quality and parental investment. Moreover, whether it’s the male or the female that builds the nest is also species dependent. It’s predominantly females that build the nests, as seen in the titmouse species. However, some species including sparrows, doves, and sunbirds have been observed building nests together. 

Many birds will only use their nest for one breeding season and then build a new one to raise their next brood. However, a few species including the Golden Eagle and Osprey will continue to reuse their nests year after year. Conversely, some species avoid this energy-consuming task altogether. 

Cuckoo birds are brood parasites and will lay their eggs in another bird’s nest. Once they hatch, cuckoo chicks will push the host young out of the nest. Some species do not use nests at all, such as Emperor penguins who lay their eggs directly onto the icy ground. 

How Long Do Birds Incubate Eggs Before They Hatch?

The incubation period varies depending on the species of bird that laid the clutch. However, on average, incubation periods last between 10 and 30 days. Incubation is the act of keeping eggs warm, usually via the mother sitting on them, in order for embryos to properly develop inside the egg. 

Generally, smaller species have a shorter incubation period compared to larger species. Songbird species do not begin the incubation process until all their eggs have been laid. This is to ensure synchronous embryonic development and hatching, which makes parental care easier. 

The warbling white-eye has the shortest incubation period out of all the avian species, being around only 9-10 days. European starlings incubate their eggs for around 12 days whilst the pileated woodpecker incubation period lasts around 18 days. Canada geese have a long incubation period of 28 days.

Do Male Birds Help Raise Chicks?

Parental care strategies vary throughout different avian species. Yet, the majority of bird species, around 81% exhibit biparental care. Roughly 8% show maternal care and only 1% show paternal care. The remaining 9% of species demonstrate cooperative breeding.

Parental care behaviors in birds include nest building, provisioning offspring with food, and defending their nest and chicks from predators.

Are Birds Monogamous?

The majority of bird species, around 90%, are monogamous. This means they only have one sexual partner at a time. This contrasts with mammal species as only 5% show monogamy and the rest show polygamy. 

Polygamy means having more than one sexual partner at a time. This is because it’s evolutionarily advantageous for birds to partake in biparental care. Parental investment in bird species is large, and often one parent will incubate the eggs whilst the other parent collects food. Once the chicks have fledged the nest, the mating pair will either stay together or find a new partner. 

A large number of avian species do mate for life, including black vultures, swans, and the aptly named love birds. However, although it’s a small number, some birds do show polygamous behavior. These species include salt marsh sparrows, wild turkeys, and house wrens. 

Solved: Do Birds Get Pregnant? 

Birds copulate through an act known as “cloaca kissing”. Although fertilization is internal, embryonic development is external. Once females have laid their fertilized eggs, they will be incubated until they are ready to hatch and eventually fledge the nest. 

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