Bird eggs. Why do birds have different eggs?
The central part of the egg is occupied by the yolk. It consists of 5-6 alternating concentric layers of yellow and light colors, and the yellow color is much wider than the light color (up to 2.8 mm versus 0.25-0.40 mm). It is believed that every two adjacent layers (dark and light) are formed within one day. The center of the yolk consists of a light substance - latebra, which has the shape of a flask and is connected through a neck to the embryonic part of the egg (in an unfertilized egg - with a blastodisc, in a fertilized egg - with a germinal disc). The yolk is always oriented with the embryonic part upward, which has important adaptive significance during egg incubation. The substance of the yolk consists of balls, larger in its yellow layers (up to 0.15 mm in diameter).
The yolk is covered with an elastic vitelline membrane about 0.024 mm thick. The shape of the yolk is slightly oblong towards the poles of the egg and slightly flattened at the blastodisc. The color of the yolk ranges from pale yellow to dark orange. It contains essential nutrients.
Egg white consists of four fractions. Directly around the yolk there is a thin layer of internal dense, or hailstone, protein, from which hailstones (chalaza) stretch towards the poles of the egg. They are firmly attached on one side to the surface of the yolk, and on the other to the outer dense white and thus, as if by stretch marks, hold the yolk in the center of the egg. The hailstone protein is surrounded by a thicker layer of internal liquid protein, consisting of a semi-viscous homogeneous substance, similar in density to the yolk. The yolk, being suspended in this layer, is well protected from sudden movements inside the egg.
The inner liquid and dense protein, together with the yolk, are placed in the so-called protein sac, which is a thick layer of the outer dense protein.
The protein sac at the sharp and blunt poles of the egg is attached to the inner shell membrane. It contains many mucin fibers, which help maintain its shape and serve to protect the yolk.
Between the albumen sac and the subshell films (except for the poles) there is a fourth layer - the outer liquid protein, which is very similar in consistency to the inner liquid. The approximate volume of the mentioned layers in a chicken egg is, %: hailstone - 3; internal liquid - 17; protein sac - 57; external liquid - 23.
The protein is a later formation in the evolution of birds and has less structural stability than the yolk. It mainly has a protective function, being at the same time a reservoir of water.
The protein is surrounded by shell membranes. The inner (protein) shell covers the entire protein and is tightly fused to the outer shell. In the region of the obtuse pole, the commissure between them is weakened. After the egg is laid and cooled, the yolk and white slightly decrease in volume, at the blunt pole the shell membranes separate, and an air chamber forms between them. On average, the mass of the shell shells of chicken eggs is 0.36 g, which is approximately 0.6% of the mass of the egg, and their thickness is 0.06-0.07 mm.
The air chamber immediately after cooling of the egg has a diameter of less than 1 cm, then it increases depending on the storage period, temperature and humidity of the surrounding air. The size of the air chamber, other things being equal, is an indicator of the freshness of the eggs.
The egg is covered with a hard calcareous shell - a shell, which protects its contents from mechanical damage and is a difficult barrier to microbial infection and water evaporation. The thickness of the shell varies greatly, mainly due to the outer spongy layer. Chicken eggs have an average shell thickness of close to 0.35 mm. In thick-shelled eggs it is thicker at the sharp pole, and in eggs with a very thin shell it is thicker at the blunt pole. In the “equator” zone, the thickness of the shell is more constant and mainly characterizes the average for a given egg.
The shell is riddled with pores, the number of which in a chicken egg is usually more than 7 thousand, and per 1 cm 2 - more than 100. The pores vary significantly in size, which, taking into account their number, determines the rate of weight loss of the egg during storage and incubation.
The last, outermost shell of the egg - the cuticle, consisting mainly of mucin, covers the surface and pores of the shell with a thin layer (5-10 microns). The cuticle is tightly connected to the shell, but is quite easily washed off with hot water and is damaged by friction. The shell takes on a shiny appearance. By this sign you can judge the quality of the egg. However, some chickens lay eggs whose shells are practically devoid of cuticle.
Thus, the yolk is surrounded by four protein layers, two subshell films, a shell and a cuticle, i.e. eight shells, each of which performs its own specific function.
The excretory system includes two kidneys, which remove waste products from the blood and form urine. Birds do not have a bladder, and the water passes through the ureters directly into the cloaca, where most of the water is absorbed back into the body.
The reproductive system consists of the gonads, or sex glands, and the tubes extending from them. Male gonads are a pair of testes in which male reproductive cells (gametes) - sperm are formed.
The female gonads, the ovaries, form female gametes - eggs. Most birds have only one ovary, the left one. Compared to a microscopic sperm, an egg is huge.
Fertilization in birds is internal. Sperm enter the female's cloaca during copulation and swim up the oviduct. Fertilization, i.e. the fusion of male and female gametes occurs at its upper end before the egg is covered with protein, soft membranes and shell.
Brood- these are birds whose chicks are able to see, hear, run and feed independently almost immediately after hatching from the egg. They need parental care, but do not stay in the nest for a long time, like chicks. One parent or both birds accompany the chicks until they fly.
U chicks In birds, the clutch is usually smaller than in brood birds; the number of eggs in it is determined by how many chicks the parents can feed. In broods, the number of clutches depends on how many eggs the hen can fit under her. The nest of representatives of the nestling group is usually more complex and massive than that of the brood group, well camouflaged and insulated with soft material. Such a structure camouflages the chicks from prying eyes and protects them from bad weather.
U nesting the opposite is true - their chicks hatch naked, blind and helpless. In the first days they need constant heating, and their parents bring them food until they leave the nest and even longer. Such chicks leave their home without really knowing how to fly. At this time they are called fledglings. Chick birds include all songbirds, or passerines, as well as swifts, rakshas, woodpeckers, cuckoos and others.
By habitat There are four groups of birds:
- Forest birds They differ from other groups in that they have rather small legs, as well as medium-sized heads. Their neck is not visible, their eyes are on the sides.
- Birds of the coasts of reservoirs and swamps has a very long neck and long legs. They need them to get food in the swamps.
- Birds of open spaces They are adapted to migration and therefore have very strong wings. Their bones weigh less than those of other types of birds.
- The last group are waterfowl who live near or in bodies of water. These birds are distinguished by a fairly powerful beak, which helps them feed on fish.
There are five groups of birds in total. nesting sites. The main difference is only in the type of nest in which these birds live:
- Crown-nesting birds they build their nests, as the name suggests, in the crown of trees (orioles, zabliki).
- Bush birds they place their nests near or in the bushes themselves (wren, robin).
- Ground-nesting decide to place their nest directly on the ground (larks, pipits, buntings, waders).
- Hollow-nesting birds live directly in hollows (woodpeckers, tits, pikas, flycatchers).
- And the last group of birds, burrowers(shore swallows, bee-eaters, kingfishers), live in burrows, underground.
- Go to the section table of contents: * Bird reproduction, mating behavior
Bird eggs
Birds reproduce by laying eggs. There are a huge number of variations in size, color, shell structure, etc. and so on.
The bird lays an egg in about a day. This process includes the time from the release of the egg from the ovary, the formation of the egg membrane and the actual laying of a fully formed egg. Unlike oviparous reptiles, a bird usually lays only one egg at a time. However, a chicken from the American city of Mandham set a kind of record - she laid 421 eggs in 223 days.
Eggshells contain a lot of calcium salts, which birds try to include in excess in their diet. Therefore, for example, female penguins, in preparation for laying eggs, swallow a large number of mussel shells and other mollusks. In this way, the penguins receive additional calcium, which is necessary for the construction of the shell, which makes it stronger. Such eggs have a better chance of not breaking if accidentally hit by stones, ice or other hard surfaces.
The eggs of many birds, while still in the oviduct, just before laying, are coated with special dyes. This or that color of the eggs makes them less noticeable against the background of the nest and the surrounding area. That is why, in birds nesting in hollows and other closed places, eggs are usually monochromatic - white and bluish. But in birds that build open nests, eggs often have a special characteristic pattern and color, serving as a protective coloring and playing a protective role. Therefore, in some species the surface of the egg is covered with specks, sometimes forming a rim around the blunt end, while in others the entire surface is covered with colored streaks or blurry spots.
And the surface of the egg can be either rough or smooth, matte or shiny. And the shape of the eggs of most birds resembles chicken eggs, but there are many exceptions. So in kingfishers they are almost spherical, in hummingbirds they are elongated and blunt at both ends, and in waders they are very pointed at one end.
And the color of eggs of various birds covers almost the entire spectrum. Even chickens have green eggs! Japanese breeders have developed a new breed of chickens that lay soft green eggs. It is believed that such an effect is determined by the specific properties of the spleen of these birds. It turned out that green eggs contain more B vitamins and iron.
On the outside, the eggshell is covered with a thin soluble film that has bactericidal properties and protects the egg from the penetration of microbes. Therefore, bird eggs: chicken, quail and others intended for storage, in order not to damage this protective film, should not be washed in water.
Most birds lay a very specific number of eggs during one breeding cycle: from 1-3 to 10-20, and sometimes more eggs. Therefore, in birds like the California condor, which lay one egg every two years, each pair adds only “half an individual” to the population per year, and species with 2-3 large clutches of eggs per year can increase it by 20-30 or more individuals.
Incubation is the most important period in egg development. In some species, both partners can participate in the incubation of eggs, in others only one of them, the male or female. A bird that incubates its eggs usually develops one or two brood patches, patches of skin located on the underside of the chest that are devoid of feathers. The skin of the brood spot, intensively supplied with blood, is in direct contact with the eggs and transfers parental warmth to them. The incubation period, ending with the hatching of the chicks, lasts from 11–12 days in small passerines to approximately 82 days in the wandering albatross.
Brightly colored males, as a rule, do not sit on eggs if the nest is open. The exception is the Red-breasted Grosbeak, which not only incubates, but also sings. In many partners who alternate incubating eggs, the brooding instinct is so strong that at times one bird pushes the other off the nest to take its place. If only one partner is incubating, he will periodically leave the nest to feed and bathe.
Only the male incubates the eggs of the ostrich (Struthio). In this case, several females lay eggs at once, and the male rolls them into the nest, incubates them and actively protects them. There are usually from 15-20 eggs in a nest, up to 50-60.
The round or elongated shape of the egg depends on whether the bird likes to fly.
Bird eggs are difficult to confuse with something else, but their appearance is still very diverse. And if everything is more or less clear with coloring - the color of the shell makes the eggs invisible, and, moreover, without parents - then with the form there is no such clarity.
And the shape of eggs in different species can differ quite greatly, for example, in waders, the eggs at one end narrow quite strongly, so that they look like a pear, in owls, the eggs are spherical and resemble tennis balls, and in hummingbirds they are bean-shaped. All eggs have the same function - to protect and nourish the chick during its embryonic development; This means that the variety of forms arose for some extraneous reason.
Mary Stoddart ( Mary Stoddard) from Princeton University and Lakshminarayanan Mahadevan ( Lakshminarayanan Mahadevan) from Harvard, together with colleagues from other research centers, analyzed the geometric shape of almost 50,000 eggs belonging to 1,400 species of birds. The researchers even developed a special program that could be used to accurately determine how different an egg is from a perfect ball.
Eggs, as we said, are very different, very elongated, not very elongated, with a pointed end, etc., and various geometric features are combined with each other in different ways. However, as it turned out, there are no eggs in the world that are short and pointed - that is, not a single bird lays eggs that look like a balloon.
The shape of the egg actually depends not on the shell itself, but on the soft membrane - the subshell membrane, which initially contains the entire contents of the egg; the shell appears later, when the egg has already formed. The membrane has thicker and less thick sections, somewhere it stretches more, somewhere weaker - all in order to be strong enough to withstand the pressure from inside the egg as it grows and swells in the bird's genital tract. As calculations have shown, a variety of geometric shapes are suitable for this. However, in theory, it turned out that one of such solutions could well be the shape of a balloon, meanwhile, as we said, there are no such eggs in nature.
Then the researchers tried to compare the eggs with the behavior of birds. Among the thousands of species that were chosen for analysis, it was possible to identify several groups with eggs of similar shape. However, there was no relationship between the shape and type of nest, or the choice of nesting site, or the number of eggs in a clutch (although both have often been put forward in the past as explanations for the variety of egg geometry). The coincidence was found in another way: it turned out that the shape of the eggs often corresponds to the parameters of the wing, the ratio of its length and width.
The length and width of the wing determine the flight pattern - in other words, the geometry of the eggs depended on how the bird flies. Those who fly well and spend a lot of time in the air (like albatrosses and hummingbirds) have elongated and asymmetrical eggs; if birds take to the air reluctantly, spend a lot of time on the ground or fly short distances from bush to bush and from tree to tree (such as African pittas and trogons), then their eggs will be more rounded. To calmly lay a rounded egg, we need a wide oviduct and a wide pelvis, but if we want to fly quickly and maneuver in flight, the body must be light and elongated, and a wide pelvis is not at all appropriate here. (Presumably, the same applies to birds that swim and dive a lot - they also need a narrow, streamlined body shape.)
That is, various combinations of elongation and pointedness are all the results of attempts to combine the need for a narrow oviduct with the need to supply the egg with a sufficient amount of nutrients. The combination of a spherical shape with a sharp end (like the notorious balloon) turns out to be meaningless - the pointedness gives an advantage only if the egg is also elongated; if the bird flies little and therefore can afford spherical eggs, then the sharp end will simply be unprofitable because it will reduce the volume of the egg.
Original taken from pystelgga in Bird's eggs
As they say, a precious egg for Christ’s Day. With Easter approaching, it's time to talk a little about what distinguishes the reproductive processes in birds from similar processes in mammals, namely eggs.
All birds lay eggs. There are no exceptions. The size of the egg depends on the size of the bird, and the shape depends on its living conditions. If it lays eggs in a hole, they are round; in the nest - oval; if it nests on rock ledges, it is oblong. Coloration also varies greatly because the eggs must be invisible to surrounding predators. If a bird builds a nest in which the eggs are not visible, then they may be white; if it nests on the ground, then the eggs can be grayish, variegated, green, etc., to match the color of grass or stones. The thickness of the eggshell also depends on the nesting conditions. Interestingly, eggs breathe through many microscopic pores in the shell.
The largest eggs, as is known, are laid by the female African ostrich: weight up to 2 kg, length - 15-20 cm; the smallest are dwarf hummingbirds: weight less than 0.4 g, length up to 1 cm. There are exceptions to the rules: the relatively small kiwi bird (5 kg) lays eggs the size of 1/4 of its body. (In the small gray kiwi, the yolk content in the egg is 65% (while in other birds it is no more than 35-40%). Thanks to this amount of yolk, a newly hatched chick can go without food for up to 10 days). The weight of a standard chicken egg is 47-50 grams; goose - 160-200 g; turkey - 75-90; quail - 12-15 g.
This is what the eggs of the inhabitants of our forests look like: 
And these are plover eggs:
Blackbird eggs: 
Tinamou bird eggs from the South American tropics: 
(By the way, the weight of a tinamu’s heart is only 0.002 of its body weight, which is why these birds are extremely reluctant to fly).
Lapwing eggs: 
This is a product consisting of chicken protein and yolk. Due to their rich composition, they are also called a treasure in a shell: they contain vitamins A, B, E, K, D (in terms of content they are second only to fish), as well as calcium, phosphorus, iron, manganese, iodine and amino acids. The product is high in calories (an egg weighing 50 g contains about 75 kcal), so nutritionists advise starting the day with it in order to enjoy the feeling of fullness longer. Also, eggs must be in the diet of children and athletes, especially bodybuilders, because they are a source of protein.
Opinions vary regarding how many eggs should be in the diet, but most nutritionists agree that it is undesirable to eat more than 10 eggs. in Week.
Goose
Goose eggs have appeared in the human diet since the domestication of geese. This dates back to the Neolithic era - about 10 thousand years BC. Goose eggs belong to dietary products, the nutritional value of which is several times higher than chicken eggs. The egg is quite large - weighing about 200 g with a white shell. Goose eggs have a fairly dense shell, so to prepare hard-boiled eggs, you need to boil them for 15 minutes in salted water, covered, over medium heat. Also, goose eggs are quite dirty and should be washed under running water before use. In terms of fat content, eggs are significantly inferior to duck eggs. Depending on the bird's diet, the taste of the eggs also changes. The more fresh grass they have in their diet, the more delicate their taste.
Pigeon
Pigeon eggs are quite small, 4 cm long. Almost all types of pigeons have white eggs without speckles, with a pearlescent, shiny tint, but in some breeds the eggs are light brown or cream in color. Pigeon eggs have very fragile shells, making them difficult to transport and requiring careful handling.
Turkey
These eggs are the closest in consumer properties to chicken eggs. The average turkey egg weighs 70-75 g. The shell is quite dense, usually white with a creamy tint and small lighter specks. The size and color of eggs directly depends on the age of the bird; the younger it is, the smaller the eggs and the lighter the shell.
Chicken
A chicken lays an egg on average every 24-26 hours. White eggs are laid by white chickens, and brown eggs are laid by red or dark chickens. In terms of nutritional value, white and brown eggs are no different. The size of the eggs depends on the age, weight and breed of the chickens. More mature hens lay larger eggs. Stress factors also affect the size of eggs: increased temperature, limited space, poor chicken nutrition, etc.
Quail
A quail egg is considered a dietary product necessary in the diet for the normal development of a child’s body, for recovery in the postoperative period and for various diseases. The egg has a fairly thin, light-colored shell with characteristic dark spots. The weight of one quail egg ranges from 10 to 12 g.
Quail eggs and their beneficial properties have been known to mankind since the times of Ancient Egypt. The Japanese conducted research into the properties of quail eggs in modern society, and the publication of scientific articles on the benefits of this type of egg made quail eggs world famous.
Ostrich
Ostrich eggs have a high commercial value and are not among the main products of ostrich farming and, practically, all are sent for incubation. In the diet, unfertilized eggs are used - table eggs, eggs obtained from young females, early or late eggs. Ostrich eggs are in no way inferior to chicken eggs and are prepared in a similar way. One ostrich egg holds 25-40 chicken eggs and weighs from 450 g to 1800 g; its resemblance to porcelain allows the shell to be used in artistic products by painting and engraving it. The world's largest ostrich egg, weighing 2.35 kg and with a diameter of 18.67 cm, was registered in China.
Duck
Duck eggs are the most high-calorie waterfowl eggs, which contain a large amount of fat and at the same time they have a specific smell and taste. The weight of an average duck egg is 90 g, which is 1.5-2 times more than a chicken egg. The shell of eggs is dense, and its color can vary from white to bluish-green. In some countries, duck eggs are considered a very expensive delicacy. This is how canned duck eggs are prepared in Japan. In China they are stored for a hundred days, but for this they use an aqueous solution to which green tea, potash, salt and burnt oak bark are added. In the Philippines, duck eggs are cooked when the chick inside is already fully formed (beak, plumage, skeleton). The dish is called "balut".
Pheasant
Pheasant eggs are literally a storehouse of all kinds of useful substances and various vitamins. They are small in size, about half the size of chicken eggs. Pheasant eggs can be colored sand, dark gray, gray, light gray, greenish gray, light green, green and almost marsh colors, and can be plain or speckled.
Guinea fowl
Refers to dietary products that have low cholesterol and hypoallergenic properties. The guinea fowl egg is pear-shaped, yellowish-brown in color and has a very dense shell. That is why they are easy to transport and there is less chance of salmonella infection. Eggs retain their beneficial properties and freshness for quite a long time (up to six months) at a temperature of 0-10°C. The average guinea fowl egg weighs 45-48 g. In most European countries, more guinea fowl are bred than chickens.
Turtle
A very nutritious and rare product that is considered a special delicacy. This type of egg is round in shape, white in color and has a soft leathery shell. The mass of the egg is 30-35 g. The yolk has a color from pale to bright yellow, and in size and taste is very close to chicken. The protein, in turn, has a gelatinous structure and is completely transparent. For European countries, turtle eggs are exotic and considered a great delicacy. In eastern countries, this product is an everyday food.
emu
Emu eggs are healthy, just like chicken eggs. They don't even differ in their cooking methods. The weight of one egg is from 450 g. up to 1800g, which is equal to approximately 25-40 chicken eggs. The largest egg with a diameter of 18.67 cm and a weight of 2350 g. was registered in China. The shell of an emu egg is very dense and durable, despite this it is quite easy to break. It is dark green, almost black, and the eggs themselves have a rich yolk and translucent white.
