Yes, most bird species will sit on their eggs constantly until they hatch in order to keep them warm and protected. The parent birds take turns incubating the eggs, only leaving the nest for brief periods to eat and drink. This constant brooding behavior is necessary for successful hatching.
What is egg incubation?
Incubation refers to the process by which certain birds, reptiles, amphibians, and invertebrates keep their eggs warm until they hatch. In birds, body heat is transferred from the parent bird to the embryo inside the egg, allowing it to develop. The temperature must be kept within a narrow range for the embryo to develop properly. Too low and the embryo will not develop; too high and the embryo will die.
Bird eggs have a specialized local area of heat production in the embryo called the heat-concentrating brood patch. It allows efficient transfer of warmth from the adult bird’s body to the egg during incubation. The eggs must be turned regularly to prevent the embryo from sticking to the inside of the shell. Both male and female parent birds assist with egg turning and incubation in most bird species.
Why do parent birds sit on their eggs?
Birds do not have the ability to regulate the temperature inside their eggs like mammals do in the womb. Bird embryos are ectotherms, meaning they rely on external heat to provide the proper incubation temperature. Parent birds must transfer their own body heat by sitting on top of the eggs in order to keep them within the optimal incubation temperature range.
If the eggs are not incubated, the embryos inside will quickly die from lack of warmth. Some key reasons parent birds must sit constantly on their eggs include:
Maintaining proper temperature
As mentioned, bird eggs must be kept at a temperature between 99-102°F for ideal incubation. Fluctuations above or below this narrow range can harm the developing embryo. The parent bird’s body heat keeps the temperature constant.
Allowing gas exchange
The porous shell of the egg allows oxygen to diffuse in and carbon dioxide to diffuse out. However, this gas exchange happens most efficiently when the bird is sitting on the eggs. Their body heat stimulates the flow of gases.
Preventing water loss
Like gases, water is exchanged through the porous eggshell throughout incubation. Sitting on the eggs creates higher humidity around them which reduces moisture loss. Too much water loss can be detrimental to the embryo’s development.
Protecting from predators
If left unattended, the eggs are vulnerable to predators and parasites looking for an easy meal. Birds sitting on the nest act as the first line of defense against anything trying to eat the eggs.
Shielding from temperature fluctuations
The weather can sometimes change rapidly, exposing the eggs to swings in temperature and humidity. An attentive parent sitting on the eggs acts as insulation to protect from these shifts.
When do birds start sitting on the eggs?
Birds typically begin sitting on their eggs as soon as the first one is laid. For species that create a complete clutch before incubating, full-time incubation generally begins after the last egg is laid. However, some species, including many songbirds, shorebirds, and seabirds, begin incubating right away.
Some reasons birds incubate from the first egg include:
Preventing embryos from sticking
If allowed to sit for too long before incubation, the developing embryo may start to adhere to the inside of the shell. Turning the eggs helps prevent this problem.
Ensuring all hatch together
In species that incubate from the first egg, the staggered hatch times allow the first few hatchlings to have a slight head start on growth and development before the others join them. This size hierarchy can help reduce sibling rivalry.
Synchronizing hatching with food
Birds like seabirds and migratory species that rely on seasonal food sources benefit from timing incubating from the first egg to line up the hatching with peak food availability.
How long do parent birds sit on the nest?
The total time parent birds must sit on the nest varies widely depending on the species. Some averages include:
Small songbirds
– Incubation period: 11-15 days
– Hours per day on nest: Approximately 75%
Parrots
– Incubation period: 3-4 weeks
– Hours per day on nest: Nearly 100%
Chickens
– Incubation period: 21 days
– Hours per day on nest: Almost constantly
Ducks
– Incubation period: 28 days
– Hours per day on nest: 80-90%
Emperor Penguins
– Incubation period: About 65 days
– Male on nest: Constantly 24/7 for ~115 days total!
In general, smaller birds have shorter incubation periods and may spend a bit less time on the nest per day because they lose heat faster than larger birds. The Emperor Penguin endures the longest single incubation shift of any bird species.
Do both the male and female bird sit on the nest?
In most bird species, both the male and female parent will take turns incubating the eggs. They trade off brooding duties, allowing each parent to take breaks to find food and exercise. However, in some species, only one sex takes on the bulk of nest sitting:
Female-only incubators
In bird species where the male plays no part in chick rearing, such as ostriches, ducks, and chickens, only the female bird sits on the nest. Females have specialized featherless brood patches for maximal heat transfer.
Male-only incubators
Male-only incubators include ostriches, Emperor Penguins, and emus where only males possess brood patches. Females deposit the eggs and leave nest care completely to the male.
Shared duties
In most songbirds, raptors, doves, owls, and other species, males and females share incubation duties equally. This provides each parent time off the nest to replenish energy reserves needed to care for the hatchlings.
Do parent birds ever leave the nest?
While parent birds spend most of their time sitting on the eggs during incubation, they do still periodically leave the nest for essential activities like:
Eating
Incubating adults need to eat regularly to maintain their own health and energy. For arduous incubators like Emperor Penguins, body reserves are built up before incubation starts.
Drinking
Sitting adults lose water over time and need to drink water to avoid dehydration. Most take quick sips nearby and return immediately.
Defecating
Adults will briefly rise off the eggs to defecate away from the nest to keep it clean. Some songbirds even eat the fecal sacs of their hatchlings to keep the nest sanitary.
Stretching
Remaining in one position on the eggs can be taxing. Brief activity breaks help muscles stay limber and prevent pressure sores.
Socializing
In colonial nesters, incubating parents may interact briefly with their neighbors to maintain social bonds.
Their time off the nest is kept as brief as possible. If the weather is poor or predators abound, they may not leave for extended periods. Most have adapted efficient incubating strategies to balance their duties.
What happens late in the incubation period?
As the hatching time approaches, the chick embryos become more active within their shells. Parent birds can feel them moving and may adjust position to distribute heat more evenly. If deprived of heat, unhatched chicks may begin cheeping from inside their shells. At this point disturbance of the nest can cause premature hatching.
Just prior to hatching, the chick will start pipping – using its egg tooth to break through the shell. It can take many hours of pipping and resting before the chick fully emerges. Once external piping occurs, the parents may help the chick by removing bits of broken shell.
As the hatching process finishes, the chicks are very vulnerable and need constant brooding to stay warm until their down dries and fluffs up. Parents are extremely protective during this period. The personal bond between parents and chicks begins forming right from the moment of hatching.
Conclusion
Incubation represents a huge investment of time and energy for parent birds. Their constant sitting on the nest is crucial for developing the embryos into healthy hatchlings. While an exhausting process, it also facilitates extraordinary bonds between avian parents and offspring that continue on after hatching. The payoff for the parents is the perpetuation of their genes and offspring that may one day reproduce and incubate their own clutch of eggs.