A hundred kinds of birds with a variety of mouths.
Some have beaks larger than their heads, and some have beaks longer than their bodies. Some have mouth shells that are curved like a crescent moon, and some whose mouth shells are straight like spears.
Birds have different diets, body sizes, and living environments, and the shape and size of their beak shells are also different. The ever-changing bird's beak is inseparable from its origin, and the size, length and curvature of the bird's beak conform to a certain law of change. According to the law, just tell you how the birds prey, or let you listen to the birds' songs, you can guess the shape of the beak shell of this bird that you have never seen before. The reverse is also true, you see the beak shell of a bird, you can guess what its main food is, and whether the chirping tone is high or low.
Birds with different shapes and shapes have the same destination, and there are 3 kinds of uses: one is to prey, the second is to sing, and the third is to dissipate heat. In addition, for birds without forelimbs, the beak is still a tool for nesting, combing, and fighting, but these complex factors do not affect the general law, and do not mention it.
Next, according to the classification of climate, diet and bird song, we will look at the shape of the bird's beak.
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The beak is the same size as the limbs of a walking beast, and obeys Allen's Rule. Allen, the first president of the American Union of Ornithologists, proposed this summary of biological laws named after him in 1877.
Allen's Rule: Extensions of the body of warm-blooded animals, such as limbs, tails, ears, and mouth, vary depending on the temperature. Animals living in cold areas are shorter and longer animals living in warm areas. Simply put, when it is cold, the body is clustered together, and reducing the surface area is conducive to heat preservation. When it is hot, the body stretches and expands, and increasing the surface area is conducive to heat dissipation.
Although Allen's law is an established principle recognized by the biological community, there is not much quantitative evidence. Sounds like a lot of sense, is the simple and rough Allen's law right? A team from the University of Melbourne in Australia confirmed the correct rule with measured data from local parrots: the parrot's beak changes with temperature, and the hotter it is, the larger the beak.
Birds have a higher body temperature than we do, and temperatures affect them more. The bird's beak, exposed in the air, is covered with blood vessels on the shell of the mouth without feathers, and is an important organ for the exchange of heat between the bird and the outside world. You see birds sleeping with their mouths tucked under their wings, which is thermal insulation. Birds are often independent on one leg when they are in the water, and one leg can reduce the heat dissipation of the legs by half compared to the legs. Birds living in Australia do not have to worry about heat preservation, on the contrary, heat dissipation is the focus of their consideration. Over the past century, global temperatures have risen, and Australian parrots have changed their mouth size as temperatures change.
The team measured specimens of 410 parrots in the museum and obtained comparative data from 1871 to 2008, confirming that the size of the beak conformed to Allen's law.
There are a total of 5 species of parrots, of which 4 species have significantly enlarged beaks. The Muraga parrot (Psephotellus varius), the red-crowned cockatoo (Callocephalon fimbriatum), the red-waisted parrot (Psephotus haematonotus), the crimson rose parrot (Platycercus elegans), from 1871 to 2008, increased the surface area of the parrot's beak by 4 to 10 percent.
In just over 100 years, the size of the parrot's beak has changed significantly. The size of the beak and the heat dissipation capacity are not simply linear, increasing the surface area of the beak shell by 10% and increasing the cooling capacity by more than 10%. Especially in extremely hot environments, large birds' beaks have more advantages.
A joint team from the Okinawa Institute of Science and Technology (OIST) and the Czech Biological Laboratory, also from Australian birds, measured the shape of the beak shells of 158 species of honey-sucking birds in Australia and found that the beak shells of honey-sucking birds were consistent with the size of the parrot's beaks. In the coldest winters, the bird's beak is the smallest. In the warm winters, the size of the beak increases.
The image above is a map of Australian summer and winter temperatures, corresponding to changes in the size of birds' beak shells.
The picture above shows the change in the beak shell of the yellow-billed honey-sucking bird (Meliphaga flavirictus), with low temperatures having a greater impact than high temperatures.
In addition, in addition to temperature, humidity also has an impact on the size of the bird's beak. In humid summers, it is more difficult to dissipate heat from humidity, which also means that birds have to grow larger beak shells. [Headlines - France is Bacon - Please do not reprint other platforms without authorization]
<h1 class="pgc-h-arrow-right" > food</h1>
Climate affects the size of the beak, while food affects the shape of the beak shell.
The spark of evolution is ignited by the shape of the bird's beak. In 1835, Darwin landed on galapagos island in the Pacific Ocean and saw many birds on the island that looked similar, but the shape of the beak was clearly different. When Darwin observed birds, he found that birds with different beak shell shapes ate different foods. Birds with short beaks eat small, soft fruits, and birds with thick beaks eat nuts with hard shells. Perhaps these similar-looking birds had the same ancestor, and later evolved into different shapes of bird beaks because of different food choices. Speculation about the evolution of the bird's beak opened the door to Darwin's thinking about natural selection. The birds on galapagos island are also named: Darwin's finch.
The birds we are familiar with eat differently and have different mouth shapes. For example, hummingbirds have slender beak shells that can suck nectar like a straw. The swallow has a short, wide beak shell and can hold insects in flight. The owl bends its hooked beak shell to catch a mouse and plunge it into the flesh. The flattened beak shell of the domestic duck can filter out the water when swallowing the dried shrimp in a large mouth. However, the domestic goose, which is also a waterfowl, has a different shape from that of a duck.
Dr. Olsen of the University of Chicago measured the mouth shape of 42 species, a total of 136 game birds (goose-shaped order), and analyzed the details of the change in the mouth shape of the birds that ingested different foods.
Pictured above is the shape of a bird's beak in a game bird.
Studies have found that the mouth shape of the birds is suitable for filter feeding. As omnivorous birds eat more and more vegetarian food, the duck-like beak gradually changes to a goose-like beak.
The image above is a classification of the mouths of ducks, geese, and swans, and here, geese belong to the goose class. The change in mouth shape from left to right in the figure corresponds to an increase in the amount of vegetarian food in the bird's diet, a decrease in the amount of small fish and shrimp, and an increase in the leverage of the mouth shell.
The picture above is a classification of the food eaten by birds with different mouth shapes, and the connection between food and mouth shape is clearly visible. However, food is not the only factor affecting the shape of the beak, the bird's beak shell grows on the head, and the evolution of the bird's beak is also constrained by the shape of the skull.
In addition to eating, birds also sing, and the size and shape of the mouth will affect the bird's voice.
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A joint team of the Okinawa Institute of Science and Technology (OIST) and the Czech Biological Laboratory measured the shape of the beaks of 525 honey-sucking birds in 101 species, analyzed 711 matching recordings of bird songs, and identified the corresponding sound changes in the shape of the beak shell.
The image above is the team's analysis of the shape of the mouth, which has a clear correspondence with the call. Among honey-sucking birds, birds with large beaks and shells have a slow song rhythm. Birds with smaller beaks and shorter calls. Birds with long and narrow beaks not only have a lower voice, but also sing a longer voice. Other details of the mouth shape, such as curved curvature, width and narrow variations, have no noticeable effect on sound. Also, as you might guess, the larger the honey-sucking bird, the lower its voice.
The team collected data on native Australian honey-sucking birds. The Australian honey-sucking bird originated in humid subtropical regions, and after coming to Australia, it was separated from other regions by wallace lines and evolved separately on the Australian continent. In the process of adapting to the arid inland, honey-sucking birds have evolved different morphologies and behaviors.
The shape of the beak of the honey-sucking bird reflects the result of a combination of functions. Analyzing the shape of the bird's beak when it regulates body temperature, eating, and chirping, we can more clearly understand the laws of evolution.
In the process of evolution, the change of the bird's beak cannot be the most preferred for each univariate. Thus, there is the now kaleidoscopic shape of the mouth, plus colorful colors. It is the path of evolution that brings us a variety of biological worlds.
#科学知多少 #
Resources:
1：“Climate‐related spatial and temporal variation in bill morphology over the past century in Australian parrots”，Daniel J E Campbell-Tennant et al., Journal of Biogeography, 2015
2：“Spatial variation in avian bill size is associated with humidity in summer among Australian passerines”， Janet L. Gardner et al., Climate Change Responses，2016
3：“The shapes of bird beaks are highly controlled by nondietary factors”， Jen A. Bright et al., Proceedings of the National Academy of Sciences, 2016
4：“Evolution of a multifunctional trait: shared effects of foraging ecology and thermoregulation on beak morphology, with consequences for song evolution”，Nicholas R. Friedman et al., Proceedings of the Royal Society B: Biological Sciences, 2019
P.S. Today we update the secret series of articles in nature, which is the 29th article: Beak Size.