evolution's role in bird color patterns

[matthew809]

Take these birds for example:

My question is.... According to evolution, how did these birds get their very specific, detailed color schemes?

If evolution is true, then my guess would be that it's an arbitrary product of the bird brain via selective mating. I figure that the ancestors of these birds developed a very specific desire to mate only with other birds demonstrating a specific color pattern. Now of course this color pattern variation would be only very slightly offset from the norm... lets say the norm started as a solid gray color. Perhaps one bird was born with a slightly more bluish area of feathers at the tip of the wing, barely distinguishable from the rest of the gray. I imagine that this freak bird must have appeared so sexy to all the other birds, that they lost all desire to mate with any bird other than this bluish wing-tipped bird. So then, the next generation of these birds would all have an increased tendency for the bluish wing tip, and of course the necessarily-correlated desire only to mate with other bluish wing tipped birds. This extremely unlikely pattern of selective mating based on color patterns must have continued to the present day, with every successive generation of birds developing a slightly offset color pattern and correlated mating preferences.

I don't know much about birds or evolution, so I'm sure I must be wrong. So please educate me... according to evolution, how exactly did these birds get their color patterns?

 

[cosmictraveler]

The red of the Northern Cardinal comes from a class of pigments called carotenoids. Carotenoids are produced by plants, and are acquired by eating plants or by eating something that has eaten a plant. Carotenoids are responsible for the bright yellows seen in goldfinches and Yellow Warblers as well as the brilliant orangish yellow of the male Blackburnian Warbler. Carotenoids can interact with melanins to produce colors like the olive-green of the female Scarlet Tanager.

Please read about many other ways that they get their colors:


http://www.google.com/url?sa=t&sour...9r3KCQ&usg=AFQjCNFETPPGUPHUQ4TaNOsrT9PNLJHWNg

http://www.google.com/url?sa=t&sour...9r3KCQ&usg=AFQjCNG-SsLi4voUWBppPSH3byAUtKxvMg

 

[Pete]

Visual features that distinguish one species from another, or between males and females, are beneficial - they help in finding a compatible mate (same species, opposite sex).

And if sexual selection latches onto a feature, it can radically amplify small differences, sometimes to the point of ludicrousness: Fisherian runaway

 

[matthew809]

Visual features that distinguish one species from another, or between males and females, are beneficial - they help in finding a compatible mate (same species, opposite sex).

Back in the time when these hypothetical ancestors where all solid gray, wouldn't it have been more beneficial to keep the status quo, since it seemed to work fine for them up to that point?

And if sexual selection latches onto a feature, it can radically amplify small differences, sometimes to the point of ludicrousness: Fisherian runaway

To me, the fisherian runaway concept(if it's true) suggests that birds have a compulsive tendency to sexually focus on specific yet arbitrary color features of the opposite sex. While at the same time, and contradictorily, this idea suggests that birds have a compulsion to disregard these same formally appealing features when something different comes along. Once a more attractive bird appears in the community, will the other birds simply choose not to mate at all if it can't mate with that sexier bird? If so, then wouldn't this non-mating tendency based on nit-picky "racism" quickly bring the species to an end? Or, if the birds continue to mate with other normal birds (because they are in fact not really that nit-picky), then wouldn't the "sexier" offspring be just as likely to mate with the normal birds as they would with sexier birds. How could any one insignificant trait come to dominate the gene pool?

 

[Pete]

Back in the time when these hypothetical ancestors where all solid gray, wouldn't it have been more beneficial to keep the status quo, since it seemed to work fine for them up to that point?

Was there such a time?
And no... "working fine" doesn't mean "can't be better".
And even if it can't be better in a particular environment... the environment has a nasty habit of changing.

To me, the fisherian runaway concept(if it's true) suggests that birds have a compulsive tendency to sexually focus on specific yet arbitrary color features of the opposite sex.

No, that's not what it implies.

If I understand it correctly, it says that if some tendency to prefer some feature exists, then there will be selective pressure to amplify that tendency.

A simple example is that a tendency to prefer tail a little longer than the average will tend to be amplified over time to result in much longer tails.

Coloring and pattern preferences are obviously more complex, and the resulting sexual selection amplification is less predictable and potentially chaotic.

 

[Pete]

I should probably also point out that predator and prey interactions also impose selective pressures on visual patterns.

The resulting selection pressures are complex and dynamic, changing as predators, prey and the environment changes.

 

[spidergoat]

If all similar species of birds were grey, then they would wasted a lot of time mating with the wrong species. But the OP is correct, it's about sexual selection.

 

[Me-Ki-Gal]

Yeah we like the girls with wild hair the most . Big boobs too. Well not Me . I like little titties too and as far as the wild hair if you don't I can mess it up for you if you like

 

[matthew809]

Coloring and pattern preferences are obviously more complex, and the resulting sexual selection amplification is less predictable and potentially chaotic.

I should probably also point out that predator and prey interactions also impose selective pressures on visual patterns.

The resulting selection pressures are complex and dynamic, changing as predators, prey and the environment changes.

It's not enough to say that the evolutionary processes are complex. It must be proven that evolution is responsible for such remarkable patterns.

How is it that seemingly random sexual preferences of billions of birds over time could possibly result in such refined edges, thoughtful patterns, beauty, and balance?

It seems more likely that such precise color patterns would be lost over time and generations, rather than further detail and definition be gained. At the very most, one might expect to find chaotic color patterns with no overall visual appeal- at least not to humans.

 

[spidergoat]

The reason is that color, combined with behavior, illustrate to a potential mate the fitness of the bearer. The symmetry of it is generated by the innate bi-lateral symmetry of most vertebrates.

 

[origin]

It's not enough to say that the evolutionary processes are complex. It must be proven that evolution is responsible for such remarkable patterns.

Really? What other mechanism could account for it? Seems pretty simple actually.

How is it that seemingly random sexual preferences of billions of birds over time could possibly result in such refined edges, thoughtful patterns, beauty, and balance?

You find these patterns beautiful? I guess mrs. bird does too. Ever notice how the females are generally more drab - it would make a lot of sense in an evolutionary aspect for the female who sits on a nest to be more drab.

It seems more likely that such precise color patterns would be lost over time and generations, rather than further detail and definition be gained. At the very most, one might expect to find chaotic color patterns with no overall visual appeal- at least not to humans.

That doesn't make sense to me. If the color makes it more likely that the males and females find each other and it is not a handicap (increased predation for instance) then the vivid colors are a great survival technique.

 

[Fraggle Rocker]

My question is.... According to evolution, how did these birds get their very specific, detailed color schemes?

Looks clearly like camouflage to me. Camouflage can accomplish either or both of two things:

• Make a predator difficult to spot so it can sneak up on its prey.
• Make prey difficult to spot so it can hide from its predators.

Without looking up this particular species, my guess is that its splashy multi-colored pattern is rain forest camouflage, blending in with a riot of colorful foliage, where a solid blob of grey plumage might actually be conspicuous. Furthermore, if in this particular case it is prey camouflage, the way that can work is that even if a predator spots it, it has a hard time figuring out where the various body parts are--which red stripe is part of the bird and which is a nearby leaf or flower--so its attack may be mis-aimed and it may end up spitting out a mouthful of feathers and leaves.

If evolution is true, then my guess would be that it's an arbitrary product of the bird brain via selective mating.

As an (amateur) aviculturist, I can assure you that in most species the majority of a bird's mating decisions are based on a courtship ritual, rather than anatomy and coloration. Many ground-dwelling birds do an actual mating dance so mating is a talent contest.

In many other species the ritual is an attempt to show how fantastically good the individual will be as a mate and/or as a parent. In some species the males build elaborate, well-decorated nests and the female takes a tour and chooses the one that looks like the largest, safest, most comfortable place to raise chicks, as well as having a few tchotchkes integrated into the construction for visual appeal. In psittacine species (the parrot order, including macaws, cockatoos, Amazons, budgies, parakeets, conures, etc.), in which both parents usually share the childrearing duties, the typical courtship ritual involves regurgitating food, to show how adept each one will be at feeding the chicks. If you've ever owned a parrot, he's probably done this for you, since you're the closest thing he's got to a mate.

I figure that the ancestors of these birds developed a very specific desire to mate only with other birds demonstrating a specific color pattern.

In many species of birds the appearance may vary as much between one individual and another as it does between two cats, so clearly this is not always a primary factor in courtship. Geographically separated populations may, of course, develop their own gene pool with a signature coloration, yet when circumstances bring them together again they do not hesitate to interbreed.

This can even happen hundreds of thousands of years later when the two populations have evolved into distinct species. When the European occupiers cut down the forest along the Mississippi River that separated the eastern Rose-Breasted Grosbeak from the western Black-Headed Grosbeak, and replaced it with farms and orchards that kindly provided a steady source of foods that both species love, inter-species dating soon became commonplace, and today hybrid grosbeaks can be found all the way on the other side of the Rocky Mountains in California. Apparently, although their physical appearance changed so dramatically that a human might not even realize that the two birds are closely related species, they still use the same courtship rituals.

Now of course this color pattern variation would be only very slightly offset from the norm... lets say the norm started as a solid gray color. . . .

I'll skip over the rest of your hypothesis since it does not seem to be consistent with the empirical evidence. Consider it peer-reviewed and respectfully rejected.

There is, however one visual aspect to bird courtship which answers a question that has puzzled humans forever, with an explanation that we could not possibly have figured out until quite recently.

The question is about dimorphism. Very few birds are dimorphic. Peacocks, the Eclectus parrot, all in all an almost insignificant number of species. The males and females of all the other species are identical in appearance.

Whoops, we were wrong about that, and the reason is that we don't see the way birds do. Like many animals, it was recently discovered that their eyes have ultraviolet color receptors. Their feathers have ultraviolet pigmentation, which allows them to distinguish males from females as easily as we can tell a Ferrari from a Toyota!

I don't know much about birds or evolution, so I'm sure I must be wrong. So please educate me... according to evolution, how exactly did these birds get their color patterns?

We all appreciate your respectful demeanor and I've done my best to reply in kind. I have not answered your question about how they got their color patterns, but I have at least narrowed down the possible hypotheses by eliminating this one.

Bear in mind that in many species of organisms--perhaps most--coloration is controlled by a small number of genes. Because of this it can change rather quickly compared to many other characteristics. This is why two tribes of Indo-Europeans who sauntered off into regions with vastly different levels of solar radiation a mere four thousand years ago--only a few hundred generations--evolved into both the light-skinned Lithuanians and the dark-skinned Bengalis.

My point is that since coloration is so volatile, it's not so strange that it can become so splashy and that two related species can look remarkably different. Or even two individuals of the same species. Its role in sexual selection seems to be minor, at best, and it may be primarily the result of mutation, genetic drift and genetic bottlenecks.

 

[origin]

Looks clearly like camouflage to me. Camouflage can accomplish either or both of two things:

• Make a predator difficult to spot so it can sneak up on its prey.
• Make prey difficult to spot so it can hide from its predators.

Without looking up this particular species, my guess is that its splashy multi-colored pattern is rain forest camouflage, blending in with a riot of colorful foliage, where a solid blob of grey plumage might actually be conspicuous. Furthermore, if in this particular case it is prey camouflage, the way that can work is that even if a predator spots it, it has a hard time figuring out where the various body parts are--which red stripe is part of the bird and which is a nearby leaf or flower--so its attack may be mis-aimed and it may end up spitting out a mouthful of feathers and leaves.As an (amateur) aviculturist, I can assure you that in most species the majority of a bird's mating decisions are based on a courtship ritual, rather than anatomy and coloration. Many ground-dwelling birds do an actual mating dance so mating is a talent contest.

In many other species the ritual is an attempt to show how fantastically good the individual will be as a mate and/or as a parent. In some species the males build elaborate, well-decorated nests and the female takes a tour and chooses the one that looks like the largest, safest, most comfortable place to raise chicks, as well as having a few tchotchkes integrated into the construction for visual appeal. In psittacine species (the parrot order, including macaws, cockatoos, Amazons, budgies, parakeets, conures, etc.), in which both parents usually share the childrearing duties, the typical courtship ritual involves regurgitating food, to show how adept each one will be at feeding the chicks. If you've ever owned a parrot, he's probably done this for you, since you're the closest thing he's got to a mate.In many species of birds the appearance may vary as much between one individual and another as it does between two cats, so clearly this is not always a primary factor in courtship. Geographically separated populations may, of course, develop their own gene pool with a signature coloration, yet when circumstances bring them together again they do not hesitate to interbreed.

This can even happen hundreds of thousands of years later when the two populations have evolved into distinct species. When the European occupiers cut down the forest along the Mississippi River that separated the eastern Rose-Breasted Grosbeak from the western Black-Headed Grosbeak, and replaced it with farms and orchards that kindly provided a steady source of foods that both species love, inter-species dating soon became commonplace, and today hybrid grosbeaks can be found all the way on the other side of the Rocky Mountains in California. Apparently, although their physical appearance changed so dramatically that a human might not even realize that the two birds are closely related species, they still use the same courtship rituals.I'll skip over the rest of your hypothesis since it does not seem to be consistent with the empirical evidence. Consider it peer-reviewed and respectfully rejected.

There is, however one visual aspect to bird courtship which answers a question that has puzzled humans forever, with an explanation that we could not possibly have figured out until quite recently.

The question is about dimorphism. Very few birds are dimorphic. Peacocks, the Eclectus parrot, all in all an almost insignificant number of species. The males and females of all the other species are identical in appearance.

Whoops, we were wrong about that, and the reason is that we don't see the way birds do. Like many animals, it was recently discovered that their eyes have ultraviolet color receptors. Their feathers have ultraviolet pigmentation, which allows them to distinguish males from females as easily as we can tell a Ferrari from a Toyota!We all appreciate your respectful demeanor and I've done my best to reply in kind. I have not answered your question about how they got their color patterns, but I have at least narrowed down the possible hypotheses by eliminating this one.

Bear in mind that in many species of organisms--perhaps most--coloration is controlled by a small number of genes. Because of this it can change rather quickly compared to many other characteristics. This is why two tribes of Indo-Europeans who sauntered off into regions with vastly different levels of solar radiation a mere four thousand years ago--only a few hundred generations--evolved into both the light-skinned Lithuanians and the dark-skinned Bengalis.

My point is that since coloration is so volatile, it's not so strange that it can become so splashy and that two related species can look remarkably different. Or even two individuals of the same species. Its role in sexual selection seems to be minor, at best, and it may be primarily the result of mutation, genetic drift and genetic bottlenecks.

Nice post!

In my neck of the woods I have noticed that ground nesters are usually very subdued in color but strikingly marked to break up their patterns. The birds in my area also often lose their bright colors in the winter molt, such as gold finches, but of course some do not like the northern cardinal.

I strongly suspect that the color of birds did not occurr several thousand years ago by the direct hand of God.

Edited to add: I'll bet you a nickel that those birds in the OP are some species of Kingfisher.

 

[matthew809]

The reason is that color, combined with behavior, illustrate to a potential mate the fitness of the bearer.

I understand how these characteristics(color and behavior) would result in a steady breed of bird over time, with a fairly static color pattern.

What I don't understand is how this pattern could form in the first place. How could birds with such precise sexual preferences result, over time, in any pattern other than the original? This suggests that sexual preferences are not rigid, but more lax, and open to change. But, if sexual preferences were lax, then how could such precise patterns emerge?

It seems like a paradox to me. What am I missing here?

 

[spidergoat]

It's self-reinforcing. If a bird, for whatever reason (say random chance), chooses a mate with a certain characteristic, it's offspring will also share a desire for that characteristic. There will be variations that emphasize that characteristic, and the trait can become larger or more elaborate. Females that don't share that desire will find less suitable mates and so become less numerous. The only limiting factor is survival. Sometimes, as with a peacock's tail, the characteristic can interfere with the ability to flee predators. But still, the strongest males will be able to carry a large tail and flee from predators

 

[matthew809]

We all appreciate your respectful demeanor and I've done my best to reply in kind.

I do appreciate all the respectful responses as well, and the information therein.

It's self-reinforcing. If a bird, for whatever reason (say random chance), chooses a mate with a certain characteristic, it's offspring will also share a desire for that characteristic.

Bird A: has a freak blue patch around it's eye.
Bird B: has a freak attraction for the blue patch around bird A's eye.

They mate and 5 babies are born.

1)How likely would this trait from bird A(blue patch) be passed down to it's offspring?
2)How likely would this trait from bird B(blue patch fetish) be passed down to it's offspring?
3)Would all the offspring be the same(blue patch and blue patch fetish)?
4)Assuming that these baby birds must eventually mate with birds of the larger gene pool without these traits, what effect would the larger gene pool have on future generations.
5)Wouldn't the larger gene pool also contain countless other traits and trait preferences popping in and out of existence over generations? Why would any single trait dominate the gene pool, unless it was absolutely necessary for survival?

 

[spidergoat]

It's very likely that the desire for the blue patch would be passed down. It's also very likely that growing the blue patch would be passed down. Any success on the part of birds with blue-patch preference would tend also to increase the reproductive success of blue-patched birds, leading to a kind of arms race.

It's not that this one trait would dominate the gene pool, successful traits are always intermixing. It's likely that eventually, blue-patch preference would combine with other successful genes, because all things being equal, other traits are important too.

 

[matthew809]

It's not that this one trait would dominate the gene pool, successful traits are always intermixing. It's likely that eventually, blue-patch preference would combine with other successful genes, because all things being equal, other traits are important too.

At what point would this blue patch appear on the other eye, to become a symmetric feature?

Wouldn't many other color traits all combining produce more of a chaotic mess, rather than what we see today?

Also, much like many birth marks on humans, many assumed color "traits" may not be hereditary at all. For example, if a person was born with a dark patch over his eye, how likely is it that this would be passed on to his child?

 

[spidergoat]

The symmetry would probably start at the beginning. Symmetry can be an indicator of health. The fractal nature of genetic algorithms determining color can result in remarkable patterns rather than chaos. Unless chaos is better (as with camouflage). The formation of patterns is not a huge problem in biology.

Humans possess little genetic variation, and few people have patterned skin. I can only think of one exception and that is freckles.

 

[Pete]

It's not enough to say that the evolutionary processes are complex. It must be proven that evolution is responsible for such remarkable patterns.

I think it's enough to demonstrate that the remarkable patterns are consistent with evolution.

How is it that seemingly random sexual preferences of billions of birds over time could possibly result in such refined edges, thoughtful patterns, beauty, and balance?

Here's the ultra-simplified version, matt:
Visual attractiveness = sexual attractiveness

Think about what it is that makes something visually appealing to humans. There are some fairly fundamental universal principles involved.

It seems more likely that such precise color patterns would be lost over time and generations, rather than further detail and definition be gained.

Why?

At the very most, one might expect to find chaotic color patterns with no overall visual appeal- at least not to humans.

I don't think so.

Elegant patterns which are visually pleasing to humans are also easy to recognize.

The more chaotic a pattern, the more complex the neural programming required to recognize it.