Take, for example, to compare a female and a male peacock. The female looks very much like a chicken - an unprepossessing grayish bird. However, what a good male he is - the brightest bright plumage.
Male birds are always more beautiful in their plumage than females, why did nature order this?
In nature, everything is thought out to the smallest detail, and it is not for nothing that male birds have such bright colors. Firstly, with their flashy plumage, males attract females for mating, and secondly, with the same plumage they scare off other males (in other words, their own potential competitors).
Why do females have such pale plumage?
Since females hatch chicks from laid eggs. And sitting in a nest on her own laid eggs, the female should be very invisible to possible predators. Females, while incubating eggs, actually connect with tree branches and do not have colorful plumage.
This is how nature has thought out everything down to the smallest detail (down to the feather). An unprepossessing female herself chooses a male for mating; she looks at the plumage and at the courage and strength of the male.
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Take, for example, to compare a female and a male peacock. The female looks very much like a chicken - an unprepossessing grayish bird. However, what a good male he is - the brightest bright plumage. Male birds are always more beautiful in their plumage than females, why did nature order this? In nature, everything is thought out to the smallest detail and it is not for nothing that male birds have such bright colors...
Many birds wear bright colors. Differently colored feathers form the most fantastic patterns, the colors of which shimmer, shine or cast in many shades.
Several coloring substances and internal structure(micro structure) of the pen. Dyes of the horny substance belong to two groups of compounds. Feathers are given all sorts of shades of brown by melanins - black or brown pigments, and from yellow to deep red - by carotenoids. Melanins are produced by the body itself, and birds obtain carotenoids from food. Therefore, the color of the plumage depends on nutrition. Melanins and carotenoids can be combined in the most incredible combinations. Many of our songbirds have a yellow-green to olive coloration obtained by mixing yellow with brown or black.
The most striking effect is created, however, not by dyes, but by so-called structural paints. White sunlight, as you probably know from physics, is made up of light waves of all the colors of the rainbow. When some of these waves are absorbed or reflected from a surface, the eye perceives it as colored. If the countless tiny particles of the surface completely reflect the light, we see a flawless white color. In snow, for example, the role of mini-mirrors (mini-reflectors) is played by ice crystals. On the feather, strongly dissected barbules and air-filled cells of the horny substance of the barbules and shaft reflect and absorb light. The blue color is given by the porous keratin layer inside the barbs. If they contain carotenoids, they develop a color palette from light yellow-green to deep purple. When the light hits the feathers, they sparkle like blue, green, red, purple, golden yellow gems.
As soon as the bird turns around, its color changes or its gloss disappears. This play of colors occurs on translucent thin layers of keratin, when light is reflected by both the upper and lower surfaces. Rainbow tints on the head and neck of a drake or in gasoline films on puddles are of the same nature. The colorful plumage of birds helps them hide from enemies, find their relatives and attract individuals of the opposite sex.
The inhabitants of tropical rain forests usually dress up in bright clothes. Unfortunately, for many bird species, their colorful plumage has served them poorly. In Cuba, for example, the tricolored macaw has disappeared. The Indians decorated themselves with flight and tail feathers and attached them to arrows. Females and males of parrots, petrels, loons, whirligigs, and swifts have the same plumage. Not in many species, especially during the mating season, it differs: the outfit of males is much brighter than that of their female friends. The well-known red-breasted bullfinches are males, and the modest brownish-gray ones are females.
It is not easy for enemies to spot a bittern painted to match the reeds and reeds: in case of danger, it stretches its neck vertically, lifts its head and, frozen in this position, becomes like a bunch of dry reed stems. If you touch it, it won't move. Coloring gives strength to feathers. Most white or very light birds, for example, gulls have black flight feathers or their ends. This edging wears much less than the white areas.
Common dipper - Cinclus cinclus
Appearance. A dark brown bird the size of a starling with very thick, non-wettable plumage. The throat, chest, and belly of Asian birds are also white; young are gray with a dark scaly pattern. Okay pl...
Alpine jackdaw
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Little birds build little nests. The nests of small hummingbirds are the size of a walnut shell, and are made of the most delicate material - moss, fluff, feathers, cobwebs. Some...
In some bird species, males are brighter colored than females, in others, both sexes are brightly colored, and in others, both males and females are faded in color. Analysis of a large data set on passerine birds has shed light on the reasons for this diversity. It turned out that the brightness of plumage in both sexes is positively correlated with body size, nesting in the tropics and the absence of long-distance migrations. Polygyny (a male mating with many females) and the lack of male care for offspring correlate with the brightness of males, but these factors contribute even more to the dullness of females, which ultimately leads to strong sexual dimorphism in coloration. Cooperative care for offspring contributes to the development of bright plumage in females. The results obtained show that female beauty in birds is sometimes the result of the passive transfer to females of a trait that is useful only to males, but in many cases it also has its own adaptive significance associated with competition between females for social status and mating partners.
According to the theory of sexual selection, the correlation between reproductive success and the number of sexual partners is usually stronger for males than for females (see links at the end of the news). Therefore, the male is “interested” in impregnating as many females as possible, while the female, as a rule, has more important things to do than to pursue maximizing the number of partners. As a result, the female reproductive resource is in short supply, while the male reproductive resource is in excess. This gives rise to intense competition between males for females. Sexual selection driven by this competition leads to the development of adaptations that increase male attractiveness to females and menacingness to competitors. Often such traits are maintained by selection even if they reduce viability (see Handicap principle).
Therefore, it is not surprising that in many animals, including birds, males are brighter colored than females. Bright coloring (like song) performs two important signaling functions: it informs females that there is a good potential partner in front of them, and males that there is something in front of them. strong competitor, with whom it is better not to mess.
On the other hand, in many birds the females are also very brightly colored. The reasons for this are less obvious (read about a similar situation with women’s songs in the news, “Elements”, 03/25/2015).
One of possible reasons- passive transfer to females of a trait that is useful only to males. The fact is that the genetic determination of a sexually dimorphic trait is generally more complex than that of a monomorphic one. For example, in order for the color to become brighter in both sexes, some mutation in one of the genes that affects color may be sufficient. But for a new trait to appear only in males, this gene must still come under the control of a genetic switch (see Cis-regulatory elements), controlled, for example, by testosterone. This makes the evolution of sexual dimorphism difficult. In other words, selection acting on one of the sexes imposes certain restrictions on the possibilities of evolution of the other sex. The selection of males based on the brightness of their color can automatically “pull” along with them the brightness of the female plumage.
But this difficulty, of course, is surmountable, since we see in nature so many cases of sexual dimorphism in color. In addition, a bright women's outfit can have its own adaptive meaning. After all, females of many species also compete with each other for certain resources - from food and territory to social status and caring males. In this case, it may also be useful for them to demonstrate their unsurpassed advantages to rivals and gentlemen with the help of bright plumage.
To understand the reasons for the amazing diversity of bird outfits, biologists from New Zealand, Australia and Germany analyzed data on all 5,983 species of passerines (the passerine order includes 61% of the species diversity modern birds), depicted in the monumental summary Handbook of the Birds of the World.
The authors developed a universal method for quantitatively assessing the brightness of color, allowing for comparison of species that are dissimilar to each other (Fig. 2). As shown in Figure 2, what was actually assessed was not the brightness or catchiness, but the “masculinity” of the color, that is, how characteristic a particular color scheme is for males, but not for female passerines. When the authors then checked which colors turned out to be “masculine” and which were “feminine”, it turned out that everything was in agreement: the first group included bright, catchy colors, and the second was mainly represented by a modest yellowish-brown range.
Thus, for males and females of each species, one number was obtained, characterizing the brightness of the color. To find out what the brightness of the plumage of females and males depends on, these numbers were compared with each other and with the parameters of lifestyle, behavior, family and social organization birds.
Some of the results obtained are shown in Fig. 3. Sophisticated statistical analysis, which took into account the structure of the phylogenetic tree and adjusted for relatedness, allowed us to reconstruct the most likely cause-and-effect relationships (Fig. 4).
1. There is a positive correlation between the brightness of male and female coloration, which cannot be completely attributed to the similar action of selection on both sexes. This means that the evolutionary genetic constraints discussed above, which lead to the passive transfer of traits beneficial to one sex (usually males) to the other (usually females), play a significant role in the evolution of coloration in passerines. This is illustrated by the thickest black arrow in Fig. 4.
2. There is a clear relationship between color brightness and body size. In larger species, both sexes are, on average, brighter in color. This can be explained by the fact that in passerines, an increase in body size reduces the chances of being eaten by a predator. Selection by predators promotes the development of camouflage coloration, while sexual (or, to use a broader term, social) selection works in the opposite direction, increasing the brightness of plumage. U small birds the first tendency outweighs, for large ones - the second.
3. Strong asymmetric sexual selection, acting predominantly on males (which is typical for polygynous species without paternal care for the offspring and with sharp dimorphism in size), contributes not only (and not even so much) to an increase in the brightness of the male outfit, but to a decrease in the brightness of the female one. As a result, sexual dimorphism in color reaches a maximum (Fig. 3d shows that in species with bright males and dull females, sexual selection is most intense). It is clear why asymmetrical sexual selection makes males bright. But why do females become faded? Two explanations can be proposed that are not mutually exclusive. Firstly, in such a situation, females, as a rule, simply have no need to be bright. Polygyny and purely female care for offspring make females such a “scarce commodity” that the task of attracting marriage partners ceases to exist for them: even the most drab and homely one will still have an excess of suitors. Competition between females for food and other resources in such species is also, as a rule, weakly expressed. Second, in this situation, the “evolutionary interests” of the two sexes (that is, the direction of selection acting on males and females) are so different that selection must support the formation of genetic switches that allow traits that are beneficial only to males not to express themselves in the female phenotype . Thus, asymmetrical sexual selection contributes to breaking the connection between male and female coloration, which was discussed above in point 1.
4. In species that breed in the tropics and do not migrate long distances, both males and females are often brightly colored. This may be due to the fact that tropical birds (and many other tropical animals) are characterized by more intense intraspecific competition. As a result, among tropical species the percentage of K-strategists is higher (see the Theory of r/K-selection): many of them have small clutches, both parents take part in caring for the offspring, and the relationship between spouses is long and cordial. In conditions of intense competition, bright coloration can perform useful signaling functions in both sexes.
5. Some birds form communities in which the chicks are cared for not only by their biological parents (cooperative breeding). In such communities, the reproductive success of both sexes strongly depends on social status and the ability to increase and maintain it, including through various signals. It was previously noted that female birds that practice cooperative care for their offspring sometimes even sing more actively than males (see: Female red-tailed buntings sing more actively and more variedly than males, “Elements”, 03/25/2015). Now we can add to this that in terms of the brightness of their plumage they are not inclined to be inferior to males. The most plausible explanation for this, again, is increased competition between females for social status, male attention and other enduring values.
Thus, the study largely clarified the evolutionary mechanisms behind the amazing diversity of male and female birds. It is characteristic that all the discovered facts fit perfectly into the theory of sexual selection and other classical evolutionary models.
Why are male birds brighter in color than females?
In order to understand why this happens, you must first understand why birds need color in the first place?
Many explanations have been given about this, but science has not yet fully exhausted this issue. The reason for the difficulty is that some birds have unusual, multi-colored plumage, while others do not. Some are like bright banners, while others are difficult to notice.
All we can do is try to find a few rules that are true for most birds. One of them is that birds with bright plumage spend most of their time in the treetops, in the air or on the water. Nondescript birds live on or near the ground.
Another rule, but with many exceptions, is that the upper parts of birds are darker than the lower parts.
These facts have led science to suggest that plumage color plays a protective role, so that birds are as invisible as possible to their enemies. This is called "protective painting". The color of snipes perfectly camouflages them in the grass of the marshes where they live. The coloring of woodcocks is very similar to fallen leaves.
But since colors protect birds, who needs it more - the male or the female? Of course, it is a female, since she incubates the eggs in the nest. Therefore, nature gave it a more inconspicuous color in order to better protect it from enemies.
Another reason for the bright plumage of males is that it helps attract a mate during mating season. Then the color of the males becomes the brightest. Even birds, as you can see, have love at first sight!
In some bird species, males are brighter colored than females, in others, both sexes are brightly colored, and in others, both males and females are faded in color. Analysis of a large data set on passerine birds has shed light on the reasons for this diversity. It turned out that the brightness of plumage in both sexes is positively correlated with body size, nesting in the tropics and the absence of long-distance migrations. Polygyny (a male mating with many females) and the lack of male care for offspring correlate with the brightness of males, but these factors contribute even more to the dullness of females, which ultimately leads to strong sexual dimorphism in coloration. Cooperative care for offspring contributes to the development of bright plumage in females. The results obtained show that female beauty in birds is sometimes the result of the passive transfer to females of a trait that is useful only to males, but in many cases it also has its own adaptive significance associated with competition between females for social status and mating partners.
According to the theory of sexual selection, the correlation between reproductive success and the number of sexual partners is usually stronger for males than for females (see links at the end of the news). Therefore, the male is “interested” in impregnating as many females as possible, while the female, as a rule, has more important things to do than to pursue maximizing the number of partners. As a result, the female reproductive resource is in short supply, while the male reproductive resource is in excess. This gives rise to intense competition between males for females. Sexual selection driven by this competition leads to the development of adaptations that increase male attractiveness to females and menacingness to competitors. Often such traits are maintained by selection even if they reduce viability (see Handicap principle).
Therefore, it is not surprising that in many animals, including birds, males are brighter colored than females. Bright coloring (like song) performs two important signaling functions: it informs females that they have a good potential partner, and males that they have a strong competitor with whom it is better not to get involved.
One of the possible reasons is the passive transfer to females of a trait that is useful only to males. The fact is that the genetic determination of a sexually dimorphic trait is generally more complex than that of a monomorphic one. For example, in order for the color to become brighter in both sexes, some mutation in one of the genes that affects color may be sufficient. But for a new trait to appear only in males, this gene must still come under the control of a genetic switch (see Cis-regulatory elements), controlled, for example, by testosterone. This makes the evolution of sexual dimorphism difficult. In other words, selection acting on one of the sexes imposes certain restrictions on the possibilities of evolution of the other sex. The selection of males based on the brightness of their color can automatically “pull” along with them the brightness of the female plumage.
But this difficulty, of course, is surmountable, since we see in nature so many cases of sexual dimorphism in color. In addition, a bright women's outfit can have its own adaptive meaning. After all, females of many species also compete with each other for certain resources - from food and territory to social status and caring males. In this case, it may also be useful for them to demonstrate their unsurpassed advantages to rivals and gentlemen with the help of bright plumage.
To get to the bottom of the amazing variety of bird patterns, biologists from New Zealand, Australia and Germany analyzed data on all 5,983 species of passerines (the order Passeriformes includes 61% of the species diversity of modern birds) depicted in the monumental Handbook of the Birds of the World.
The authors developed a universal method for quantitatively assessing the brightness of color, allowing for comparison of species that are dissimilar to each other (Fig. 2). As shown in Figure 2, what was actually assessed was not the brightness or catchiness, but the “masculinity” of the color, that is, how characteristic a particular color scheme is for males, but not for female passerines. When the authors then checked which colors turned out to be “masculine” and which were “feminine”, it turned out that everything was in agreement: the first group included bright, catchy colors, and the second was mainly represented by a modest yellowish-brown range.
Thus, for males and females of each species, one number was obtained, characterizing the brightness of the color. To find out what the brightness of the plumage of females and males depends on, these numbers were compared with each other and with the parameters of the lifestyle, behavior, family and social organization of birds.
Some of the results obtained are shown in Fig. 3. Sophisticated statistical analysis, which took into account the structure of the phylogenetic tree and adjusted for relatedness, allowed us to reconstruct the most likely cause-and-effect relationships (Fig. 4).
1. There is a positive correlation between the brightness of male and female coloration, which cannot be completely attributed to the similar action of selection on both sexes. This means that the evolutionary genetic constraints discussed above, which lead to the passive transfer of traits beneficial to one sex (usually males) to the other (usually females), play a significant role in the evolution of coloration in passerines. This is illustrated by the thickest black arrow in Fig. 4.
2. There is a clear relationship between color brightness and body size. In larger species, both sexes are, on average, brighter in color. This can be explained by the fact that in passerines, an increase in body size reduces the chances of being eaten by a predator. Selection by predators promotes the development of camouflage coloration, while sexual (or, to use a broader term, social) selection works in the opposite direction, increasing the brightness of plumage. In small birds the first tendency outweighs, in large birds the second tendency outweighs.
3. Strong asymmetric sexual selection, acting predominantly on males (which is typical for polygynous species without paternal care for the offspring and with sharp dimorphism in size), contributes not only (and not even so much) to an increase in the brightness of the male attire, but to a decrease in the brightness of the female. As a result, sexual dimorphism in color reaches a maximum (Fig. 3d shows that in species with bright males and dull females, sexual selection is most intense). It is clear why asymmetrical sexual selection makes males bright. But why do females become faded? Two explanations can be proposed that are not mutually exclusive. Firstly, in such a situation, females, as a rule, simply have no need to be bright. Polygyny and purely female care for offspring make females such a “scarce commodity” that the task of attracting marriage partners ceases to exist for them: even the most drab and homely one will still have an excess of suitors. Competition between females for food and other resources in such species is also, as a rule, weakly expressed. Second, in this situation, the “evolutionary interests” of the two sexes (that is, the direction of selection acting on males and females) are so different that selection must support the formation of genetic switches that allow traits that are beneficial only to males not to express themselves in the female phenotype . Thus, asymmetrical sexual selection contributes to breaking the connection between male and female coloration, which was discussed above in point 1.
4. In species that breed in the tropics and do not migrate long distances, both males and females are often brightly colored. This may be due to the fact that tropical birds (and many other tropical animals) are characterized by more intense intraspecific competition. As a result, among tropical species there is a higher percentage of K-strategists (see Theory of r/K-selection): many of them have small clutches, both parents take part in caring for the offspring, and the relationship between spouses is long and cordial. In conditions of intense competition, bright coloration can perform useful signaling functions in both sexes.
5. Some birds form communities in which the chicks are cared for not only by their biological parents (joint care of offspring, Cooperative breeding). In such communities, the reproductive success of both sexes strongly depends on social status and the ability to increase and maintain it, including with the help of various signals. It was previously noted that female birds that practice cooperative care for their offspring sometimes even sing more actively than males. Now we can add to this that in terms of the brightness of their plumage they are not inclined to be inferior to males. The most plausible explanation for this, again, is increased competition between females for social status, male attention and other enduring values.
Thus, the study largely clarified the evolutionary mechanisms behind the amazing diversity of male and female birds. It is characteristic that all the discovered facts fit perfectly into the theory of sexual selection and other classical evolutionary models.
Source: James Dale, Cody J. Dey, Kaspar Delhey, Bart Kempenaers & Mihai Valcu. The effects of life history and sexual selection on male and female plumage coloration // Nature. Published online 04 November 2015.
Alexander Markov
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