Mate Choice in Birds
Male birds are often strikingly different in plumage and size from their female counterparts. Charles Darwin concluded that exaggerated sexual differences such as the tail of a peacock or the displays of the wild turkey evolve as a result of what he called sexual selection- namely, contests among males for mates and female preferences for particular males. As potential male reproductive success increases, so does the value of the characteristics-large size, fancy plumage, intricate songs, and striking displays-that are responsible for the success. The resulting evolutionary process of sexual selection leads to differences between the sexes in size and ornamentation. Darwin’s insights into the evolutionary role of sexual selection are now largely confirmed, but the effects of competition among males, female choice, and resources other than mates connect in even more intricate ways than Darwin proposed.
Mutual assessment of prospective partners is a vita aspect of the early stages of courtship and pair formation. The ornaments and displays favored and maintained by sexual selection are those that reliably reflect the superior condition of certain males, enabling females to select the best possible mates. For example, house finch females prefer brightly colored males, which have better survival rates and are better family providers. The familiar flight displays of male bobolinks over lush fields advertise their condition. Females favor males that display longer. Such males have larger fat reserves and consequently raise more young than their neighbors do.
Why do females choose males with more elaborate plumage or displays? The good-genes hypotheses propose that exaggerated male plumage and courtship displays truthfully signal genetic or physiological superiority. Females should recognize superior males and select them to sire offspring. What aspects of genetic or physiological superiority might exaggerated courtship displays serve to indicate? One possibility would be a male’s superior survival skill. For example, the enormous tail of a peacock might actually be a handicap during flight or escape. So would be bright colors that attract predators. Males that survive to display such handicaps would have superior stamina or abilities to escape predators. Evolution would tend to favor bigger and bolder badges of this so-called handicap superiority if females preferred to mate with the males that bore such badges.
Another application of the good-genes hypotheses asserts that ornamented plumage provides an index to a male’s health, particularly its resistance to pathogens and parasites. Females could detect disease-prone males by the lower quality of their display plumage or by their reduced display stamina. Strong evidence now exists for this hypothesis. Among their many effects, parasites reduce the brightness of ultraviolet coloration of bird feathers. The glittering blue plumage of male satin bowerbirds, for example, has a single wavelength peak in the ultraviolet. The visual intensity of this peak predicts the male’s level of infection by blood parasites, because ultraviolet shine decreases with increasing infection.
Other evidence for the use of a bird’s appearance as an index to its health comes from studies of red junglefowl, which are the ancestors of domestic chickens. Marlene Zuk and her colleagues first established that hens of the red junglefowl mated more quickly with roosters bearing large, fleshy, red combs on their heads. The hens use comb size as an index to the health of a potential mate. Comb size is strongly affected by the level of the hormone testosterone, which, in turn, affects the bird’s physical condition. Intestinal worms reduce comb size, with the result that hens prefer roosters without worms over those that are infected.
The large sizes and conspicuous plumage favored in reproductive displays may be disadvantages in other regards. Large size itself requires greater energy expenditure. There is some evidence that large male red- winged blackbirds are at a disadvantage because they must sacrifice display time for feeding. Among species of North American blackbirds, males that are much larger than females tend to suffer greater mortality as nestlings. Similarly, because they grow twice as fast as females to reach their full adult size by the end of their first summer, male western capercaillie, a huge species of European grouse, are more vulnerable than females to starvation when food is scarce. And the same bright colors that announce a male’s presence to potential rivals or mates may also attract predators.
1
Male birds are often strikingly different in plumage and size from their female counterparts. Charles Darwin concluded that exaggerated sexual differences such as the tail of a peacock or the displays of the wild turkey evolve as a result of what he called sexual selection- namely, contests among males for mates and female preferences for particular males. As potential male reproductive success increases, so does the value of the characteristics-large size, fancy plumage, intricate songs, and striking displays-that are responsible for the success. The resulting evolutionary process of sexual selection leads to differences between the sexes in size and ornamentation. Darwin’s insights into the evolutionary role of sexual selection are now largely confirmed, but the effects of competition among males, female choice, and resources other than mates connect in even more intricate ways than Darwin proposed.
Which of the following can be inferred from paragraph 1 about sexual selection and birds?
AThe presence of certain body characteristics determines a female’s reproductive success.
BSexual selection has created male-female differences in some species, such as peacocks, but not in others, such as turkeys.
CDarwin’s insights on sexual selection are mainly applicable to male populations of wild turkeys and peacocks.
DSexual selection has resulted in many striking features in males because males have to compete harder for mates than females do.
2
Mutual assessment of prospective partners is a vita aspect of the early stages of courtship and pair formation. The ornaments and displays favored and maintained by sexual selection are those that reliably reflect the superior condition of certain males, enabling females to select the best possible mates. For example, house finch females prefer brightly colored males, which have better survival rates and are better family providers. The familiar flight displays of male bobolinks over lush fields advertise their condition. Females favor males that display longer. Such males have larger fat reserves and consequently raise more young than their neighbors do.
According to paragraph 2， a characteristic of successful mating behavior in male bobolinks is
Athe ability to perform long displays while flying
Bthe ability to display a high number of different flight patterns
Cthe ability to show more colors than other males do
Dthe ability to select the most productive fields to fly over
3
Why do females choose males with more elaborate plumage or displays? The good-genes hypotheses propose that exaggerated male plumage and courtship displays truthfully signal genetic or physiological superiority. Females should recognize superior males and select them to sire offspring. What aspects of genetic or physiological superiority might exaggerated courtship displays serve to indicate? One possibility would be a male’s superior survival skill. For example, the enormous tail of a peacock might actually be a handicap during flight or escape. So would be bright colors that attract predators. Males that survive to display such handicaps would have superior stamina or abilities to escape predators. Evolution would tend to favor bigger and bolder badges of this so-called handicap superiority if females preferred to mate with the males that bore such badges.
According to paragraph 3， why might females prefer mates with bright feathers and noticeable courtship displays?
AThese visually striking characteristics enable females to mate with the first males they see.
BThese characteristics allow males to protect their young by drawing predators away from the nest.
CIn order to possess these characteristics, males must be very strong or able.
DThese characteristics allow males to avoid predators by blending in with colorful or elaborate natural settings.
4
Another application of the good-genes hypotheses asserts that ornamented plumage provides an index to a male’s health, particularly its resistance to pathogens and parasites. Females could detect disease-prone males by the lower quality of their display plumage or by their reduced display stamina. Strong evidence now exists for this hypothesis. Among their many effects, parasites reduce the brightness of ultraviolet coloration of bird feathers. The glittering blue plumage of male satin bowerbirds, for example, has a single wavelength peak in the ultraviolet. The visual intensity of this peak predicts the male’s level of infection by blood parasites, because ultraviolet shine decreases with increasing infection.
The word “ornamented”in the passage is closest in meaning to
Adecorated
Bextensive
Cexposed
Dlayered
5
Another application of the good-genes hypotheses asserts that ornamented plumage provides an index to a male’s health, particularly its resistance to pathogens and parasites. Females could detect disease-prone males by the lower quality of their display plumage or by their reduced display stamina. Strong evidence now exists for this hypothesis. Among their many effects, parasites reduce the brightness of ultraviolet coloration of bird feathers. The glittering blue plumage of male satin bowerbirds, for example, has a single wavelength peak in the ultraviolet. The visual intensity of this peak predicts the male’s level of infection by blood parasites, because ultraviolet shine decreases with increasing infection.
The word “stamina”in the passage is closest in meaning to
Apredictability
Bendurance
Cease
Dsuccess
6
Another application of the good-genes hypotheses asserts that ornamented plumage provides an index to a male’s health, particularly its resistance to pathogens and parasites. Females could detect disease-prone males by the lower quality of their display plumage or by their reduced display stamina. Strong evidence now exists for this hypothesis. Among their many effects, parasites reduce the brightness of ultraviolet coloration of bird feathers. The glittering blue plumage of male satin bowerbirds, for example, has a single wavelength peak in the ultraviolet. The visual intensity of this peak predicts the male’s level of infection by blood parasites, because ultraviolet shine decreases with increasing infection.
According to paragraph 4， which of the following may be true about male birds that have brightly colored feathers?
ATheir feathers become noticeably brighter when they are ready to mate.
BTheir display stamina discourages parasites from attacking them.
CThey can easily detect whether females are infected with pathogens.
DThey probably are not suffering from disease.
7
Other evidence for the use of a bird’s appearance as an index to its health comes from studies of red junglefowl, which are the ancestors of domestic chickens. Marlene Zuk and her colleagues first established that hens of the red junglefowl mated more quickly with roosters bearing large, fleshy, red combs on their heads. The hens use comb size as an index to the health of a potential mate. Comb size is strongly affected by the level of the hormone testosterone, which, in turn, affects the bird’s physical condition. Intestinal worms reduce comb size, with the result that hens prefer roosters without worms over those that are infected.
In paragraph 5， the author discusses Marlene Zuk’s study of red junglefowl in order to
Asupport the good-genes hypothesis presented in the previous paragraph
Bcontrast the way junglefowl avoid disease with the ways other birds avoid disease
Cemphasize the frequency of mating activity in certain species of birds
Dexplain that the physical characteristics of potential mates can be misleading to females
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The large sizes and conspicuous plumage favored in reproductive displays may be disadvantages in other regards. Large size itself requires greater energy expenditure. There is some evidence that large male red- winged blackbirds are at a disadvantage because they must sacrifice display time for feeding. Among species of North American blackbirds, males that are much larger than females tend to suffer greater mortality as nestlings. Similarly, because they grow twice as fast as females to reach their full adult size by the end of their first summer, male western capercaillie, a huge species of European grouse, are more vulnerable than females to starvation when food is scarce. And the same bright colors that announce a male’s presence to potential rivals or mates may also attract predators.
Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
AThe male western capercaillie reach their adult size by the end of their first summer, twice as fast as the rate of females.
BMale western capercaillie are more likely to starve than females because they grow twice as fast.
CWestern capercaillie, a species of European grouse, are vulnerable to starvation because they are such a large species.
DWhen food is scarce, male western capercaillie are likely to decrease their rate of growth to avoid starvation.
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Why do females choose males with more elaborate plumage or displays? [■]The good-genes hypotheses propose that exaggerated male plumage and courtship displays truthfully signal genetic or physiological superiority. [■]Females should recognize superior males and select them to sire offspring. [■]What aspects of genetic or physiological superiority might exaggerated courtship displays serve to indicate? One possibility would be a male’s superior survival skill.[■] For example, the enormous tail of a peacock might actually be a handicap during flight or escape. So would be bright colors that attract predators. Males that survive to display such handicaps would have superior stamina or abilities to escape predators. Evolution would tend to favor bigger and bolder badges of this so-called handicap superiority if females preferred to mate with the males that bore such badges.
Look at the four squaresthat indicate where the following sentence could be added to the passage
There are a few different theories that have developed from research on birds and mate selection.
Where would the sentence best fit？Click on a square sentence to the passage.
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As a result of sexual selection, many male birds have developed significant differences from females of their species.
ADarwin’s insights into the evolutionary role of sexual selection have been confirmed more consistently for birds than for other animals.
BBecause females prefer males with bright colors, elaborate tails, large combs, or striking displays, these males will have more reproductive success.
CDue to the great energy expenditure required to produce and maintain bright colors and other favored traits, many male birds are smaller than their female counterparts.
DMales and females have evolved different mechanisms for evading predators because of their different reproductive needs and strategies.
EAs predicted by the good-genes hypothesis, some of the traits preferred by females have been shown to indicate a male’s good health.
FSince many genetic characteristics increase vulnerability to predators or require extra energy expenditure, a male that has those characteristics must be superior in order to survive.
