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Flamingos depend on plant-derived chemical compounds to color their feathers, legs and beaks. Photo: Flickr user longhorndave

Pop quiz: Why are flamingos pink?

If you answered that it’s because of what they eat—namely shrimp—you’re right. But there’s more to the story than you might think.

Animals naturally synthesize a pigment called melanin, which determines the color of their eyes, fur (or feathers) and skin. Pigments are chemical compounds that create color in animals by absorbing certain wavelengths of light while reflecting others. Many animals can’t create pigments other than melanin on their own. Plant life, on the other hand, can produce a variety of them, and if a large quantity is ingested, those pigments can sometimes mask the melanin produced by the animal. Thus, some animals are often colored by the flowers, roots, seeds and fruits they consume

Flamingos are born with gray plumage. They get their rosy hue pink by ingesting a type of organic pigment called a carotenoid. They obtain this through their main food source, brine shrimp, which feast on microscopic algae that naturally produce carotenoids. Enzymes in the flamingos’ liver break down the compounds into pink and orange pigment molecules, which are then deposited into the birds’ feathers, legs and beaks. If flamingos didn’t feed on brine shrimp, their blushing plumage would eventually fade.

In captivity, the birds’ diets are supplemented with carotenoids such as beta-carotene and and canthaxanthin. Beta-carotene, responsible for the orange of carrots, pumpkins and sweet potatoes, is converted in the body to vitamin A. Canthaxanthin is responsible for the color of apples, peaches, strawberries and many flowers.

Shrimp can’t produce these compounds either, so they too depend on their diet to color their tiny bodies. Flamingos, though, are arguably the best-known examples of animals dyed by what they eat. What others species get pigment from their food? Here’s a quick list:

Northern cardinals and yellow goldfinches: When these birds consume berries from the dogwood tree, they metabolize carotenoids found inside the seeds of the fruit. The red, orange and yellow pigments contribute to the birds’ vibrant red and gold plumage, which would fade in intensity with each molt if cardinals were fed a carotenoid-free diet.

Salmon: Wild salmon consume small fish and crustaceans that feed on carotenoid-producing algae, accumulating enough of the chemical compounds to turn pink. Farmed salmon are fed color additives to achieve a deeper shades of red and pink.

Nudibranchs: These shell-less mollusks absorb the pigments of their food sources into their normally white bodies, reflecting the bright colors of sponges and cnidarians, which include jellyfish and corals.

Canaries: The birds’ normal diet doesn’t alter the color of its yellow feathers, but they can turn a deep orange if they regularly consume paprika, cayenne or red pepper. These spices each contain multiple carotenoids responsible for creating and red and yellow.

Ghost ants: There’s not much more than meets the eye with ghost ants: these tropical insects get their name from their transparent abdomens. Feed them water mixed with food coloring and watch their tiny, translucent lower halves fill up with brilliantly colored liquid.

Ghost ants sip sugar water with food coloring, which is visible in their transparent abdomens. Photo by Mohamed Babu/Solent News/Rex F/AP Images

Humans: Believe it or not, if a person eats large quantities of carrots, pumpkin or anything else with tons of carotenoids, his or her skin will turn yellow-orange. In fact, the help book Baby 411 includes this question and answer:

Q: My six-month-old started solids and now his skin is turning yellow. HELP!

A: You are what you eat! Babies are often first introduced to a series of yellow vegetables (carrots, squash, sweet potatoes). All these vegetables are rich in vitamin A (carotene). This vitamin has a pigment that can collect harmlessly on the skin, producing a condition called carotinemia.

How to tell that yellow-orange skin isn’t an indication of  jaundice? The National Institutes of Health explain that “If the whites of your eyes are not yellow, you may not have jaundice.”

Scientists believe the absence of seed-dispersing birds is thinning the forests on the island of Guam. Photo by Isaac Chellman

Visitors to Guam’s forests find them quiet–eerily so: No chirping of birds can be heard overhead. But slithering in the shadows on the ground are snakes, each some six feet long. Brown tree snakes made their debut on Guam, the southernmost island in the Mariana Archipelago, when islanders were rebuilding after World War II. Most likely, they were stowaways in lumber shipments heading north through the Pacific Ocean from New Guinea. They quickly began feasting on the birds and small lizards they discovered in Guam’s dense forests, and–free to slither through the mountainous terrain without predators of their own–they completed an invasion of the island at a pace of one mile per year. By the late 1940s, the forests had largely fallen silent, and now, all of Guam’s native bird species are history.

Last fall, scientists from Rice University and the University of Guam published one of the first studies of the island’s extinct forest birds, which include species such as the Mariana fruit dove, Guam flycatcher and Rufous fantail. They focused on how the absence of birds has caused a spike in the spider population, which is 40 times greater on Guam than nearby islands.

Now, the researchers are turning their attention to the issue of Guam’s thinning forests—a consequence, they also believe, of the bird deficit. This summer they’ll launch a four-year study of 16 tree species, looking at how the loss of birds, which scatter seeds, is affecting tree distribution.

The brown tree snake has obliterated nearly all of Guam’s bird species since it was introduced during World War II. Photo by Isaac Chellman

The study has its roots in an a-ha moment that lead scientist Haldre Rogers recently had while conducting another seed-dispersal study in Guam’s forests. “I noticed that there seemed to be a lot of gaps [in the trees] and that the pioneer tree species–such as papaya and sumak–were difficult to find on Guam, compared to nearby islands,” she explained to Surprising Science. She discovered that there were in fact twice as many such gaps on Guam per unit area of forest. 

Pioneer trees, which are the first to appear after a disruption to the ecosystem and thrive in the full sunlight of open spaces in the forest, have small seeds that are consumed by small birds. “Without birds to move their seeds to these sunny spots in the forest, these quick-growing trees may be less likely to germinate or grow to their full size,” Rogers hypothesized.

The problem with such thinning is that it could change the structure of Guam’s forests. “There’s a concern that [they] may become filled with open areas and start to look more like Swiss cheese than a closed canopy forest,” Rogers said. In other words, what were once cool, dark forests could transform into hot, open sunny ones.

There are other possible explanations for the tree-thinning: An undiscovered forest disease could be targeting pioneer species, or mammals like pigs and deer might have a strong taste for the trees. But according to Rogers, there isn’t strong evidence to support either of these scenarios. The upcoming study will attempt to determine the cause definitively.

The Mariana fruit dove was driven to extinction by the brown tree snake on Guam and is highly endangered on other islands in the Mariana Archipelago. Photo by Isaac Chellman

To that end, the researchers will cut down individual trees in various spots within Guam’s forests, creating new gaps in the forest. They’ll also remove trees from locations on two nearby islands that are still brimming with birds. Then they’ll monitor how long it takes the spaces to fill in and take note of which seedlings thrive on Guam versus on the other islands. It may seem that to get their results they’re destroying what they’re trying to study, but in actuality they’re taking down a tiny percentage of the island’s trees–20 total.

Guam’s situation is similar to that of tropical regions worldwide. “Animals involved in seed-dispersal are in decline in a lot of tropical forests around the world right now,” the co-principal investigator of the study, Amy Dunham, said in a statement. “It’s very important to understand the implications of those declines.” So far scientists have looked into the role of endangered mammals like lemurs, giant tortoises (PDF) and African forest elephants (PDF) in seed dispersal, but the upcoming study will be one of the first to focus on endangered birds.

It’s also the rare study to examine what happens when seed dispersal completely ceases–Guam being the only place in the world to experience whole-island forest bird loss in modern times. “The situation on Guam–which is tragic–provides us with a unique opportunity to see what happens when all seed-dispersal services provided by animals are lost from an entire ecosystem,” Dunham said. 

The snakes, meanwhile, continue to dominate the island of Guam. The U.S. Department of Agriculture traps approximately 6,000 brown tree snakes each year, and yet there are still nearly two million slithering around the island. The snakiest patches contain 14,000 of the reptiles per square mile–one of the highest snake concentrations in the world.

In February, the Department of Agriculture embarked on a new tactic for tackling the snake problem: dropping dead mice laced with acetaminophen, which is fatal to them, into the jungle. ”We are taking this to a new phase,” Daniel Vice of the Department of Agriculture’s branch that focuses on wildlife services in Hawaii, Guam and other U.S. held Pacific Islands, said in a recent interview. “There really is no other place in the world with a snake problem like Guam.”

Roosters have an internal circadian rhythm, which keeps them crowing on schedule even when the lights are turned off. Image via Wikimedia Commons/Muhammad Mahdi Karim

Some scientists investigate the universe’s biggest mysteries, like the Higgs boson, the mysterious particle that endows all other subatomic particles with mass.

Other researchers look into questions that are, well, a bit humbler—like the age-old puzzle of whether roosters simply crow when they see light of any kind, or if they truly know to crow when the morning sun arrives.

Lofty or not, it’s the goal of science to answer all questions that arise from the natural world, from roosters to bosons and everything in between. And a new study by Japanese researchers published today in Current Biology resolves the rooster question once and for all: The birds truly do have an inner circadian rhythm that tells when to crow.

The research team, from Nagoya University, investigated via a fairly straightforward route: They put several groups of four roosters in a room for weeks at a time, turned the lights off, and let a video camera running. Although roosters can occasionally crow at any time of day, the majority of their crowing was like clockwork, peaking in frequency at time intervals roughly 24 hours apart—the time their bodies knew to be morning based on the sunlight they’d last seen before entering the experiment.

This consistency continued for about 2 weeks, then gradually began to die out. The roosters were left in the room for 4 weeks in total, and during the second half of the experiment, their crowing began occurring less regularly, at any time of day, suggesting that they do need to see the sun on a regular basis for their circadian rhythms to function properly.

In the experiment’s second part, the researchers also subjected the roosters to alternating periods of 12 hours of light and 12 hours of darkness, while using bright flashes of light and the recorded crowing of roosters (since crowing is known to be contagious) to induce crowing at different times of day. When they activated these stimuli near at or near the dawn of the roosters’ 12-hour day, crowing rates increased significantly. At other times of day, though, exposing them to sudden flashes of light or playing the sound of crowing had virtually no effect, showing that the underlying circadian cycle played a role in the birds’ response to the stimuli.

Of course, many people who live in close proximity to roosters note that they often crow in response to a random light source turning on, like a car’s headlights, no matter what time of day it is. While this may be true, the experiment shows that the odds of a rooster responding to a car’s headlights depend on how close the current time is to dawn—at some level, the rooster’s body knows whether it should be crowing or not, and responding to artificial stimuli based on this rhythm.

For the research team, all this is merely a prelude to their bigger, more complex questions: Why do roosters have a biological clock that controls crowing in the first place, and how does it work? They see the simple crowing patterns of the rooster as an entry point into better understanding the vocalizations of a range of animals. “We still do not know why a dog says ‘bow-wow’ and a cat says ‘meow,’” Takashi Yoshimura, one of the co-authors, said in a press statement. “We are interested in the mechanism of this genetically controlled behavior and believe that chickens provide an excellent model.”

A fossil of a prehistoric bird from the enantiornithine genus shows feathers on its hind legs—evidence of an extra pair of wings. Courtesy of Xiaoting Zheng et al/Science

Roughly 150 million years ago, birds began to evolve. The winged creatures we see in the skies today descended from a group of dinosaurs called theropods, which included tyrannosaurs, during a 54-million-year chunk of time known as the Jurassic period. Why the ability to fly evolved in some species is a difficult question to answer, but scientists agree that wings came to be because they must have been useful: they might have helped land-based animals leap into the air, or helped gliding creatures who flapped their arms produce thrust.

As researchers continue to probe the origin of flight, studies of fossils have shown that theropods–particularly coelurosaurian dinosaurs, which closely resemble modern birds—had large feathers on both their fore limbs and hind limbs. However, extensive evidence for these leg feathers didn’t exist in the earliest birds. But now, a new examination of fossils reported today in the journal Science reveals several examples of this four-winged anatomy in modern birds’ oldest common ancestors.

Modern birds have two types of feathers: vaned feathers that cover the outside of the body, and the down feathers that grow underneath them. Researchers studying the approximately 120 million-year-old fossils of 11 primitive birds from the Shandong Tianyu Museum of Natural History in China found that one type of vaned plumage, also known as pennaceous feathers, was neatly preserved in skeletal fossils of these specimens, along each creatures’ hind limbs. After this find, the researchers must have been flying high: The feathers of birds’ wings, known as flight feathers, are long, stiff and asymmetrically shaped pennaceous feathers, similar to those found in the fossils. When fanned together, pennaceous feathers form the broad surfaces of birds’ wingspans—without these surfaces, birds cannot stay aloft.

Pennaceous feathers, which are composed of many flattened barbs, existed in some winged dinosaurs. Finding them on the hind legs of early birds suggests that before birds used two wings to fly, they may have depended on four. Over millions of years, however, birds gradually lost the feathers on this extra set of wings.

The study adds to existing theories that suggest the first birds flew with four wings. Examination of a primitive bird fossil from the Archaeopteryx genus in 2004 revealed long feathers on the animal’s back and legs, which would have aided its gliding ability. Two years later, another study of the crow-sized animal, which lived about 150 million years ago, reported that the prehistoric bird’s feathers resembled those on modern birds’ flight wings.

One of the more complete skeletons examined in today’s study actually showed hind-limb pennaceous feathers along the bone of each leg. The longest feather stretched almost two inches, which is remarkable considering that the legs they covered were between one inch and two and a half inches long. In fact, specimens from a group of birds called Enantiornithes, which externally resemble modern birds, showed symmetrically paired large feathers preserved along their hind leg bones. Such feather arrangement is present in modern birds’ wings.

Researchers speculate that the second set of wings might have provided extra lift or created drag in the air. They might also have helped birds maneuver their airborne bodies.

If these hind wings indeed served a functional purpose in fight, they will earn an important place in bird evolution. Bird movement is characterized by a combination of feathered arms for flight and legs for walking on land. This study suggests that if walking legs, present in birds today, developed after these feathered hind legs, then the loss of feathers on the back legs—and thus an extra pair of wings—reflects a period of change during which the arms became specialized for flight and the legs, for locomotion.

Today, leg feathers are less well developed than wing feathers—they are usually much smaller and fluffy—and they serve as protection and insulation for the leg. These fluffy bits are sparse too—instead, the legs are covered in scales, which form only if feather growth is inhibited. Studies of modern birds show how this works. As chicks develop from embryos and grow into adults, feathered legs can be transformed into scaled legs, or vice versa, by altering how certain genes are expressed.

The recent revelation about feathers on birds’ hind legs suggest that a similar genetic, and more permanent, change might have occurred early in bird evolution, according to lead researchers. This shift triggered the loss of birds’ hind wings, pushing the creatures down an evolutionary path that would allow them to fly with just two.

Scientists discovered that the penguins plumage is even colder than the surrounding air, potentially allowing them to absorb heat through convection. Image © Université de Strasbourg and Centre National de la Recherche Scientifique (CNRS), Strasbourg, France

Antarctica, as you might expect, gets pretty darn cold: Temperatures as low as -40 degrees Fahrenheit are often recorded during the winter. For the creatures who live there, this extreme cold demands innovative survival strategies that enable the loss of as little heat as possible.

Scientists recently discovered that Emperor Penguins—one of Antarctica’s most celebrated species—employ a particularly unusual technique for surviving the daily chill. As detailed in an article published today in the journal Biology Letters, the birds minimize heat loss by keeping the outer surface of their plumage below the temperature of the surrounding air.

At the same time, the penguins’ thick plumage insulates their body and keeps it toasty. A team of scientists from Scotland and France recently came to the finding by analyzing thermal images (below) of penguins taken at a coastal Emperor breeding colony in Adélie Land, an area of Antarctica claimed by France.

The research drew upon theromgraphic images of the penguins collected in the wild. Image © Université de Strasbourg and Centre National de la Recherche Scientifique (CNRS), Strasbourg, France

The researchers analyzed thermographic images like this one taken over roughly a month during June 2008. During that period, the average air temperature was 0.32 degrees Fahreinheit. At the same time, the majority of the plumage covering the penguins’ bodies was even colder: the surface of their warmest body part, their feet, was an average 1.76 degrees Fahrenheit, but the plumage on their heads, chests and backs were -1.84, -7.24 and -9.76 degrees Fahrenheit respectively. Overall, nearly the entire outer surface of the penguins’ bodies was below freezing at all times, except for their eyes and beaks.

The scientists also used a computer simulation to determine how much heat was lost or gained from each part of the body—and discovered that by keeping their outer surface below air temperature, the birds might paradoxically be able to draw very slight amounts of heat from the air around them. The key to their trick is the difference between two different types of heat transfer: radiation and convection.

The penguins do lose internal body heat to the surrounding air through thermal radiation, just as our bodies do on a cold day. Because their bodies (but not surface plumage) are warmer than the surrounding air, heat gradually radiates outward over time, moving from a warmer material to a colder one. To maintain body temperature while losing heat, penguins, like all warm-blooded animals, rely on the metabolism of food.

The penguins, though, have an additional strategy. Since their outer plumage is even colder than the air, the simulation showed that they might gain back a little of this heat through thermal convection—the transfer of heat via the movement of a fluid (in this case, the air). As the cold Antarctic air cycles around their bodies, slightly warmer air comes into contact with the plumage and donates minute amounts of heat back to the penguins, then cycles away at a slightly colder temperature.

Most of this heat, the researchers note, probably doesn’t make it all the way through the plumage and back to the penguins’ bodies, but it could make a slight difference. At the very least, the method by which a penguin’s plumage wicks heat from the bitterly cold air that surrounds it helps to cancel out some of the heat that’s radiating from its interior.

And given the Emperors’ unusually demanding breeding cycle (celebrated in the documentary March of the Penguins), every bit of warmth counts. Each winter, they trek from inland coastal locations to the coast inland—walking as far as 75 miles—where they breed and incubate their eggs. After the females lay eggs, the males incubate them by balancing them on top of their feet in a pouch for roughly 64 days. Since they don’t eat anything during this entire period, conserving calories by giving up as little heat as possible is absolutely crucial.