From Shell To Yolk To Bird, We Cover It All
Bird eggs are like gems in a jeweler's window; they have varying degrees of brightness, color, and cover. The biological aesthetic of these eggs is that they’re incubated outside the bird's body. But, what's in these eggs, and how do they become birds? Let's learn all about bird eggs...
Bird eggs house growing bird embryos and provide them with the essential nutrients needed for their survival. The egg's covering or "shell" protects the embryo from dehydration and predators. The shell is also semipermeable, allowing oxygen and carbon dioxide to pass through.
In the rest of this article, I'll cover the components of a bird's egg. I'll also illustrate the process involved before the egg becomes a bird. Keep reading to learn all about bird eggs!
The eggshell is the hard outer layer of a bird's egg that protects the interior components.
According to the University of Florida, the eggshell is 95 percent calcium carbonate and is semipermeable. It allows gas exchange between the embryo and the outside air. The shell also protects the embryo from dehydration and predators.
Other components of an eggshell include:
These components work together to give the eggshell its strength and color. The color can range from white to blue, green to brown.
The next layer is the membrane, which comprises two thin layers. The inner layer is called the chalaza, and the outer layer is called the serosa. These layers are covered in the next section as they're part of a bird egg's interior.
Inside a bird's egg are the yolk, chalazae, and albumen. These are the components that ensure optimum conditions for the development of an embryo. They nourish, protect, and provide structure to the growing embryo.
Let's look at each part of a bird's egg interior and its functions.The Yolk
The yolk is the yellow part of the egg and is the primary food source for the developing embryo. It is full of protein, fat, and vitamins essential for growth. Furthermore, it contains lecithin, which helps keep the egg's yolk and albumen from mixing.
Some of the vitamins and nutrients in the egg yolk are:
Chalazae are two thick strands of protein that attach the yolk to the egg's shell. These strands project from the central part of the vitelline membrane and attach to the albumen.
According to Science Direct, egg Chalazae provides the balance needed to sustain the yolk in a steady position in the egg.
Chalazae contain fibers of lysozyme, a protein that has antibacterial properties. This helps protect the embryo from harmful bacteria.
The albumen is the white part of the egg and makes up about 60% of the total weight of an egg. It consists of water, protein, and minerals. The primary purpose of the albumen is to protect the embryo.
The albumen has two layers; the thin inner layer and the thick outer layer. The chalazae are attached to the thin inner layer. The thick outer layer comprises albumin proteins coiled into a spiral shape. This spiral shape gives the egg its strength.
As the embryo develops, the albumen provides it with water and protein. It also helps regulate the temperature inside the egg.
This is an extraembryonic epithelium that lines the entire inner surface of the eggshell. It's a thin, transparent membrane that helps protect the embryo.
The serosa comprises two layers; an inner layer called the chorion and an outer layer called the allantois.
The chorion helps to attach the embryo to the shell and provides nutrients to the developing embryo. The allantois stores waste products from the embryo and helps regulate the temperature inside the egg.
A bird's egg goes through four main stages of development to become a bird; formation, cleavage, gastrulation, and organogenesis. These stages take place inside the egg before it hatches.
Now that you know the parts of a bird's egg, you may be wondering how they play into the formation of a bird. The question lingering in your mind might be, "How do fluids and nutrients turn into a bird?"
The first stage of development is formation, which is when the egg is created. This stage starts with the hen's ovary releasing an egg cell. The egg cell then travels down the oviduct, where the sperm from the male bird fertilize it.
Once fertilized, the egg cell starts to divide and grow through DNA replication as it travels down the oviduct. The egg is then covered in membranes, albumen, and shell layers.
The formation process takes about 48 to 50 hours.
The next stage is cleavage, which is when the egg cell divides into many smaller cells. This process happens very quickly in the blastodisc and results in a ball of cells called a blastoderm.
The blastoderm divides into five to six cells interconnected by tight junctions. These are then ready to move to the gastrulation process.
During gastrulation, the blastoderm cells rearrange themselves into three layers of cells. These layers are:
According to PennState Extension, the ectoderm will become the bird's nervous system, beak, skin, and feathers. The mesoderm becomes the bird's muscles, skeleton, and circulatory system, while the endoderm develops into the bird's digestive and respiratory systems.
This process takes 24 to 48 hours.
The last stage is organogenesis, which is when the cells in each layer start to differentiate and grow into the organs they will become. It takes place during the incubation period.
At this stage, cell differences become more pronounced. The ectoderm cells will become neurons and begin to form the brain and spinal cord. The mesoderm cells start differentiating into muscle, bone, and blood cells. Finally, the endoderm cells develop into the lining of the digestive tract and respiratory system, forming a complete bird ready for hatching.
Depending on the bird species, this process takes between 10 days and 3 weeks.
These other pages of ours will answer the following questions in depth...be sure to check them out!
- Can Birds Have Eggs Without Having A Male?
- How Often Do Birds Lay Eggs?
- How Are Birds Eggs Fertilized?
Bird eggs are different in color, size, shape, and pattern. These differences are based on the habitat in which the bird nests. For instance, robin eggs are light blue because they are typically found in open habitats.
According to Illinois State University, bird egg color variation is mainly meant for camouflage purposes. Once laid, bird eggs are exposed to predators, making them vulnerable. Thus, the egg's color helps to hide the egg from predators, keeping it safe until the baby bird is ready to hatch.
Most cavity-nesting birds lay white eggs since the egg color doesn't need to provide camouflage in this type of environment. Birds that nest on the ground lay pigmented eggs to recognize parasitism by other bird species.
The size of the egg is mainly based on the bird's size. For example, a hummingbird's egg is about the size of a pea, whereas an ostrich's egg is about 15 times larger.
Finally, the shape and pattern of the eggshell are determined by the bird's habitat. In most cases, birds that nest in trees have oval-shaped eggs, while those that nest in holes have rounder eggs. The patterns on the eggshell help camouflage the egg and can be different colors, such as brown, green, or blue.
Bird eggs portray a complex and intricate design that has taken millions of years to perfect. The different colors, sizes, shapes, and patterns of bird eggs are based on the nesting environment. In most cases, the egg is designed to ensure the safety and well-being of the embryo.
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About the Author...
Richard Worden, a dedicated bird lover for over 20 years, I love to share my in-depth knowledge and passion for birds. Read more About Me and my expertise in this field.