Bird Incubation Process: How Long Does It Take for Eggs to Hatch?

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Have you ever seen a bird sitting on its nest, waiting for its eggs to hatch? If so, you have witnessed incubation. Birds reproduce by laying eggs and incubating them until they hatch. The length of time needed for the bird incubation process varies from species to species. Factors like the ambient temperature, humidity, and predatory threats all affect the incubation process. How long does it take for eggs to hatch? With more than 10,000 different species of birds in the world, the answer to that question is not as simple as it might seem.

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Incubation begins sometime after a female bird lays a fertilized egg. Some bird species begin the incubation process after laying the first egg in their clutch. Others wait to begin incubating their eggs until after they have laid the second egg. And some species wait until they have laid all the eggs in the clutch before they begin incubation. All of these strategies can have their advantages and disadvantages. In general, though, bird eggs can be held a short time under the right conditions before beginning incubation.

If a bird begins incubating after laying the first egg, the eggs may hatch in sequence. Birds that begin incubating after the second egg will most likely end up with two hatchlings that are larger and stronger than the third or fourth. Birds that wait to begin incubating all the eggs simultaneously will likely end up with all the eggs hatching at about the same time, and hatchlings of similar size and strength.

Whatever incubation method a species uses probably works best for the survival of their offspring. For instance, ground-dwelling birds that must be on the move quickly after hatching are much better off hatching simultaneously than straggling along over the course of a few days. Birds that start a clutch in cold weather in exposed nests are more likely to start incubating right away, even though that means one or more of their offspring will be at a disadvantage by developing a day or two behind its siblings.

Incubation takes anywhere from about 11 days to nearly three months, depending on the species. Generally, smaller birds take less time to complete incubation and hatch their eggs than larger birds. However, there are exceptions to that rule. Here are the incubation periods for a few familiar groups of birds.

The largest group of birds, the passerines, belong to the order Passeriformes. More than half of the known bird species belong to this order. We most commonly refer to passerines as songbirds, and the group includes many of the smallest bird species. One might think that the smallest passerines would have the shortest incubation periods, but that is not the case. Hummingbirds average about 14 days, while some warblers and finches incubate their eggs only 11 days. Most passerines that live in temperate areas average about 12 to 15 days for incubation. Some species, including a few tropical flycatchers, incubate much longer, between 17 and 26 days.

Domestic poultry represent perhaps the most well studied bird species in terms of breeding and reproduction. Domestic chickens, bred from wild fowl centuries ago, average 21 days from the time their eggs are laid until they hatch. Many domestic chicken breeds have been selectively produced to eliminate broodiness. Broodiness refers to the tendency of a bird to attempt to raise a clutch of eggs. Some breeds today resist incubating their eggs to the extent that the only reliable way to continue hatching their eggs is to incubate the eggs artificially.

Turkeys average about 28 days to incubate their eggs. Ducks, with the exception of the Muscovy duck, also average about 28 days. Muscovy ducks take about a week longer. Geese incubate their eggs for around 28 to 33 days.

Wild ducks and geese have variable incubation periods. Mallard ducks, one of the most common and recognizable species, average 28 days. Other species of ducks and geese can take as little as 21 days or up to about 33 days to hatch their eggs.

The incubation periods of birds of prey vary by species. For instance, the Bald Eagle takes approximately 35 days to incubate their eggs, while the Golden Eagle incubate their offspring for 41 to 45 days. The Great Horned Owl and the Barred Owl average about 33 days to incubate their eggs, often sitting on the nest through frigid winter temperatures. Hawks can take anywhere from 21 to 42 days, depending on the species. Red-tailed Hawks average between 28 and 35 days for incubation, while American Kestrels take 26 to 32 days. Ospreys have one of the longest incubation periods among the hawk species, taking between 36 to 42 days to hatch their young.

The ratites include mostly large, flightless birds such as ostriches, emus, cassowaries, rheas, and kiwis. Ostriches average between 36 to 45 days for incubation. Rheas take about the same amount of time, averaging 36 to 44 days. Emus take longer to incubate their eggs, between about 46 to 56 days. Cassowaries take an average of 50 days, and the males are solely responsible for incubation.

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As ratites go, the kiwis are by far the smallest. Kiwis lie the largest eggs of any known birds, proportional to their size. A female kiwi’s egg can average up to 15 percent of her body weight, so it is little wonder that she typically lays only one. The male then tends the egg through the incubation period, which can last from 74 to 90 days.

Most birds incubate their eggs by sitting on their nest and using their own bodies to keep their eggs at a near constant temperature. That temperature, for most species, is around the same as that of the human body, 98.6°F. Incubation temperatures typically hover a little below the body temperature of the parent bird. The temperature of the incubating eggs must be held within a tight range. Temperatures above about 104°F will damage or even destroy the developing egg, while temperatures below about 80.6°F are likely to cause incosistent development.

Most birds use something called the brood patch, or incubation patch, to incubate their eggs. In preparation for incubation, birds form a highly vascularized patch or patches on their underside. The feathers covering this patch fall out, or are plucked out in some species. This naked patch of skin, rich with blood vessels, provides a surface for contact with the eggs. The bird can sense the temperature in the eggs and adjust the blood flow to the brood patch, raising or lowering the temperature of their own skin to keep the eggs safe.

Not all birds develop brood patches. In many species, only the female incubates the eggs, so the males of those species do not develop brood patches at all. In species where the male is solely responsible for incubation, the females do not develop a brood patch. When both species take turns incubating their eggs, they may both develop brood patches, unless they use other means to keep their offspring warm.

Some birds, such as pelicans and penguins, use the skin on their webbed feet in place of a brood patch. They transfer body heat through their feet to their single egg. Some others, such as the megapodes of Australia, create compost heaps that generate steady heat to keep their eggs warm.

Birds must move their eggs around regularly in order to keep the membranes inside from sticking to the inner wall of the shell. Many birds turn their eggs throughout the day. Some species turn their eggs every few minutes, while others only turn them once every hour or so. Some birds build suspended nests that swing or sway in the breeze. These birds do not need to turn their eggs often, because the movement of the nest takes care of that for them.

At the end of incubation, baby birds emerge from their shells. These baby birds usually use something called an egg tooth to crack the egg from the inside before slowly pushing their way out.

Some birds are precocial, which means they hatch with a covering of soft feathers and are up and moving soon after they emerge. Some precocial ground-dwelling birds may follow their parent away from the nest on their first day.

Other birds are altricial, which means that they are relatively helpless upon hatching, usually naked and with their eyes still closed. The incubation period for altricial birds is often shorter than that of precocial birds. This makes sense, because precocial birds are more developed upon hatching than their altricial counterparts.

Observing how birds incubate their eggs can be a fascinating and fun experience. One of the most popular webcams ever, the OKC Owl Cam, featured a Great Horned Owl family that nested outside the window of a human family near Oklahoma City. Alessondra, the little girl who discovered the owls outside her window, became a celebrity at the age of five. Over several consecutive years, the OKC Owl Cam owls had millions of viewers. As the birds returned to their nesting place winter after winter, people all over the world were able to watch as the female incubated the eggs and the male provided her with food.

The mother owl sat on the nest day and night, rarely leaving to stretch her wings and give viewers a look at her eggs. She persisted through good weather and bad, enduring rain, snow, and ice, until her owlets emerged. and clear weather. And then her audience watched a few weeks more, as she raised her offspring until they were ready to fledge. All the time, the male stayed close by, periodically appearing out of the darkness with a rabbit or a rat to feed his mate and their young.

The OKC Owl Cam no longer streams live, although the family maintains an archival site with plenty of videos. However, many other bird cams do currently stream live video, some with audio, during nesting seasons. These are great tools for learning more about the incubation process, and experiencing how long it takes for eggs of various species to hatch.

Artificial incubation is another way to learn about incubation in a hands-on way. You can order incubators online or at farm stores, and you can purchase chicken eggs of many different breeds directly from a hatchery or a local farmer. The incubator does the work of maintaining a constant temperature, but required labor includes turning and checking the eggs regularly.

School children sometimes raise eggs in an artificial incubator in the classroom to learn more about the reproductive process of birds. Incubation provides an excellent opportunity for scientific observation. If incubating eggs at home, make sure you have a good plan for what to do with the chickens once they hatch. If you plan to keep them and raise backyard chickens, remember that the incubation period is only about 21 days, so maybe get your coop finished before you start incubating the eggs.

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