National Geographic Tales of the Weird

by David Braun

  Appearances Can Be Confusing

  Only about 1 in 10,000 chickens are born as gynandromorphs, which have male features—such as a rooster’s comb and a defensive leg spur—on one side of their bodies and dainty, henlike features on the other.

  Researchers had thought a rare genetic abnormality caused the condition. To test this theory, Michael Clinton of the University of Edinburgh and his team analyzed cells from three gynandromorph chickens. To their surprise, the team found that the chickens’ cells were normal. What was strange, however, was that male cells made up one half of the body, and female cells composed the other half.

  TRUTH:

  CHICKENS SEE DAYLIGHT 45 MINUTES BEFORE HUMANS DO.

  A hybrid chicken—reflected in mirrors—has both male (left) and female (right) characteristics. (Photo Credit 6.4)

  Eggs Are Double Fertilized

  The scientists believe gynandromorphs are created when a chicken egg becomes fertilized by two sperm. Despite their dual nature, the hybrid birds typically have one of the sex organs, either testes or ovaries. The scientists did not test whether the chickens could actually reproduce, however.

  Gynandromorphs are known to exist in other bird species, such as zebra finches, pigeons, and parrots, Clinton said by email. It’s likely that the phenomenon occurs in all bird species, he added, but it’s not always obvious because males and females of many species often look similar.

  THE HIGH PRICE OF DANCING

  Sexually Showy Male Birds

  Finish Early

  Among male houbara bustards, large brown birds found in North Africa, wooing females can be a tricky business because, for them, the more mating dances they do, the lower their sperm counts.

  Live fast, age fast—at least if you’re a male houbara bustard. That’s because male bustards that perform longer courtship displays lose sperm quality faster than males that do not put on elaborate seduction shows, a new study suggests.

  The sheer energy required to keep up marathon performances eventually takes its toll on the sperm production of the flashy males, which actually start out with healthier, more robust sperm than their humdrum rivals.

  TRUTH:

  HOUBARA BUSTARDS ARE HUNTED FOR THEIR MEAT, WHICH IS THOUGHT TO BE AN APHRODISIAC.

  Risky Business

  “In nature, life is very risky, so you need to balance the benefit that certain behaviors can give you at present, and the costs that these same behaviors can incur later on,” said study senior author Gabriele Sorci, an evolutionary biologist at the University of Burgundy in France.

  In the case of the bustards, Sorci thinks the showy males get the balance right, in terms of survival. In part because of the high chances of dying young in the wild, he said, “It’s always the best [reproduction] strategy to have early benefits and eventually pay a later cost.” The new study represents the first time that such a trade-off has been linked to declines in male fertility in any species, Sorci added.

  The Dance of Love

  In their North African habitat, male houbara bustards perform long displays to attract females up to six months out of the year. Some males keep at it for several hours a day and perform more often, while others invest less of their resources to luring mates.

  After strutting for a while, a male erects an ornamental “shield” of long white feathers and then runs at high speed, often circling a rock or a bush, according to the study, published recently in the journal Ecology Letters. Te show climaxes in a flash of black and white feathers and several booming calls so deep they’re almost out of range of human hearing, according to Sorci. Females will often select males that run more laps while taking fewer and shorter breaks.

  Shooting Blanks

  For the study, the team used ten years of data taken from more than 1,700 male bustards—ranging from 1 to 24 years old—at captive-breeding facilities in Morocco. Each day, workers would observe the males’ courtship behavior, which is roughly the same as in the wild. The scientists then added up the number of days the males were seen displaying, and for how long. The result was an index of “male sexual-display effort” for every year of each bird’s life.

  A male houbara bustard performs his mating dance. (Photo Credit 6.5)

  Also daily a team would place a dummy female under each male bird to initiate mating and then capture his ejaculate in a petri dish, the study says. Scientists recorded the quality of the bird’s semen—how many sperm were in each ejaculate, how well they swam, etc.

  The results showed that the most avid performers during youth released smaller quantities of semen, with more dead and abnormal sperm, at older ages. The data also uncovered a still unresolved mystery: Though these flashy males had passed their reproductive prime, the show still went on, Sorci noted.

  Fabrice Helfenstein, an evolutionary ecologist at the University of Bern in Switzerland, said via email that the study “is sound—it is based on a lot of animals and uses properly new statistical tools.” For instance, the captive birds proved useful: “Such aging processes are usually hard to reveal in wild animals,” which are generally thought to die too young to suffer the effects of aging, said Helfenstein, who was not involved in the new study.

  Like Human, Like Bird

  Male great tit birds with brighter breasts also seem to have stronger sperm, a recent study finds. This advertisement is a boon to female great tits, since finding a male with high-quality sperm isn’t always easy. This is partially due to free radicals, which threaten sperm cells in many animals, including humans. Male great tits produce an antioxidant called carotenoid that both defends against free radicals and gives their breast feathers a bright yellow hue. Similarly, some studies have shown that men with more attractive faces have better quality semen.

  Casanovas, Take Note

  In general, the idea that investing in sexually attractive traits early in life racks up costs later could possibly be applied to other species, including humans, study co-author Sorci said. For instance, showy male bustards may be the “bird equivalent of the posers who strut their stuff in bars and nightclubs every weekend,” study leader Brian Preston, also of the University of Burgundy, said in a statement. “If the bustard is anything to go by, these same guys will be reaching for their toupees sooner than they’d like.”

  BAD OMENS?

  Why Do Birds Fall From the Sky?

  In-air deaths of large groups of birds have spooked people for centuries, but what is behind the most recent rash of these seemingly ominous events?

  A mysterious rain of thousands of dead birds darkened New Year’s Eve 2010 in Arkansas, and in early January 2011 similar reports streamed in from Louisiana, Sweden, and elsewhere. But the in-air bird deaths aren’t due to some apocalyptic plague or insidious experiment—they happen all the time, scientists say. The 2011 buzz, it seems, was mainly hatched by media hype.

  At any given time there are “at least ten billion birds in North America … and there could be as much as 20 billion—and almost half die each year due to natural causes,” said ornithologist Greg Butcher, director of bird conservation for the National Audubon Society in Washington, D.C.

  But what causes dead birds to fall from the sky en masse? The Arkansas case points to two common culprits: loud noises and crashes.

  TRUTH:

  DRAMATIC DIE-OFFS ARE ACTUALLY VERY COMMON IN ANIMALS THAT CONGREGATE OR TRAVEL IN LARGE GROUPS.

  New Year’s Eve, 2010

  Beginning at roughly 11:30 p.m. on New Year’s Eve, Arkansas wildlife officers started hearing reports of birds falling from the sky in a square-mile area of the city of Beebe. Officials estimate that up to 5,000 red-winged blackbirds, European starlings, common grackles, and brown-headed cowbirds fell before midnight.

  Results from preliminary testing released by the National Wildlife Health Center in Madison, Wisconsin, show the birds died from blunt-force trauma, supporting preliminary findings released by the Arkansas Livestock and Poultry Commission.

  “They collided wi
th cars, trees, buildings, and other stationary objects,” said ornithologist Karen Rowe of the Arkansas Game and Fish Commission. “Right before they began to fall, it appears that really loud booms from professional-grade fireworks—10 to 12 of them, a few seconds apart—were reported in the general vicinity of a roost of the birds, flushing them out,” Rowe said.

  TRUTH:

  FIVE BILLION BIRDS DIE IN THE UNITED STATES EVERY YEAR.

  “There were other, legal fireworks set off at the same time that might have then forced the birds to fly lower than they normally do, below treetop level, and [these] birds have very poor night vision and do not typically fly at night.”

  The dead birds found in Arkansas are of a species that normally congregate in large groups in fall or winter. “The record I’ve heard is 23 million birds in one roost,” Audubon’s Butcher said.

  “In that context, 5,000 birds dying is a fairly small amount.”

  A Towering Problem for Birds

  Birds often hit objects in flight, especially “tall buildings in cities, or cell phone towers, or wind turbines, or power lines,” Butcher said. “The structures that seem to cause the most deaths are very tall and constantly lit,” he said. “On foggy nights, birds that should probably normally be paying attention to the stars get disoriented, and circle around the structures until they collapse” and fall.

  Collisions with power lines seem to have killed roughly 500 blackbirds and starlings in Louisiana in early January 2011. The 50 to 100 jackdaws found on a street in Sweden that same day showed no signs of disease and also apparently died from blunt-force trauma, according to the Swedish National Veterinary Institute.

  Wind, snow, hail, lightning, and other challenges posed by weather can easily kill flying birds too. For example, “last year a couple of hundred pelicans washed up by the Oregon-Washington border,” Butcher said. “A cold front had unexpectedly moved in, and they faced icing on their wings and bodies.”

  “In Arkansas … fireworks were set off in a town near a known blackbird roost. [The] birds flushed from the roost and … were seen crashing into buildings and cars and poles. Necropsies show blunt force trauma to brain and breast.”

  Melanie Driscoll

  biologist and director of bird conservation for the Gulf of Mexico and Mississippi Flyway for the National Audubon Society

  What Are the True Crises?

  Of course, death doesn’t just stalk birds from above. For instance, “waterfowl get botulism—and salmonella and avian pox can spread at bird feeders,” Butcher said.

  No matter how it arrives, death appears to be very much a fact of life for birds. “Young birds that hatch in the spring have an approximately 75 percent chance of not reaching their first birthdays,” the Arkansas Game and Fish Commission’s Rowe said.

  To biologists, these deaths are normal occurrences. “I wish I could take all this energy and attention on these deaths and direct them toward true crises in wildlife biology, to things like the white-nose syndrome in bats,” Rowe added.

  She does, though, see a silver lining in the sky-is-falling coverage in 2011. “I hope we can raise public awareness of what impact man-made structures can have on other species. How many migratory warblers do you want to kill just to get better cell phone reception?”

  YOUR EYES REVEAL ALL

  Bird With “Human” Eyes

  Knows What You’re Looking At

  The messages in our looks, glances, and gazes might be no mystery at all to the jackdaw, a blackbird with humanlike eyes.

  For the crowlike birds known as jackdaws, it’s all in the eyes. The species may be the only animal aside from humans known to understand the role of eyes in seeing and perceiving things, according to a new study.

  The Eyes Have It

  While humans often use visual clues to communicate, it wasn’t known whether other animals share this social ability. Jackdaw eyes, like those of humans, are unusually conspicuous, with dark pupils surrounded by silvery white irises.

  The physical similarities hint that jackdaws use their eyes to communicate in the same ways humans do, said study leader Auguste von Bayern, a zoologist currently with the University of Oxford. “We can communicate a lot via the eyes, and jackdaws do that as well, in my opinion,” von Bayern said.

  TRUTH:

  A BIRD’S VISION IS ITS MOST IMPORTANT SENSE.

  Now her study of hand-reared jackdaws shows that the birds—members of the same family as crows and ravens—can use a human’s gaze to tell what that person is looking at. “They are sensitive to human eyes because they are sensitive to their own species’ eyes,” von Bayern said. By contrast, previous studies have shown that other animals regarded as intelligent, such as chimpanzees and dogs, find even their own species’ eyes hard to read.

  A Eurasian jackdaw gives someone the eye. (Photo Credit 6.6)

  Conflict and Cooperation

  Von Bayern conducted the jackdaw experiments while completing her Ph.D. at the University of Cambridge. In one test, she and colleague Nathan Emery timed how long a jackdaw took to retrieve food if a person was also eyeing the prize.

  They found that the birds took longer to retrieve the food if the human was unfamiliar—someone the bird apparently didn’t trust. The birds were equally sensitive to the gaze of a single eye, such as when the person looked at the food in profile or kept one eye closed. This suggests the jackdaws made the decision to risk conflict solely based on eye motion and not on other cues, such as the direction a potential rival’s head was facing.

  In a second experiment, the birds were able to interpret a familiar human’s altered eye gaze to “cooperate” to find food that was hidden from view. The study authors add that more tests will be needed to tell if the birds were able to read eye movements based on their natural tendencies or if it is a learned behavior from being raised by humans.

  MUSICAL PLUMAGE

  Bird “Sings”

  Through Feathers

  Most birds twitter and chirp through their beaks, but the feathers of this South American songbird make a music all their own.

  Solving a long-standing puzzle among bird experts, scientists have found that the sharp, violin-like sounds of a South American songbird come not from the beak but from a suite of specially evolved, vibrating feathers.

  “I was just utterly stunned. There’s literally no bird in the world that does anything that prepares you for it. It’s totally unique.”

  Richard Prum

  ornithologist, Yale University, on hearing a club-winged manakin “sing” with its feathers for the first time

  Club-Winged Manakin Music

  A new study offers the first hard evidence that birds use feathers for audible communication as well as for flight and warmth. In 2005 Kimberly Bostwick theorized that the male club-winged manakin—a tiny bird of the Andean cloud forest—was vibrating a club-shaped wing feather against a neighboring, ridged feather to “sing” when trying to attract females. Proving the feather-song connection, though, would be a huge challenge.

  “It was very hard to mess with the birds’ feathers and still have them do their display,” said Bostwick, curator of birds and mammals at the Cornell University of Vertebrates in Ithaca, New York. “There were many times where I listened to the sound and started doubting that a feather could possibly make [the sound],” she recalled.

  Bird Vibrations

  To determine, once and for all, how the manakin was making its bizarre sounds, Bostwick and colleagues decided to take feather samples and analyze them in a lab.

  She knew from previous work that the frequency of the sound made by the manakin was 1500 hertz—1,500 cycles per second. If the two feather types were making the sound, they should resonate when vibrated at the same frequency during the experiments. The team used lasers to monitor vibrations as they were oscillated by a lab device called a mini-shaker. The special feathers vibrated at exactly 1,500 hertz—proving they’re responsible for the strange sounds.

  But there�
�s a twist: Bostwick was surprised to find that the club and ridged feathers aren’t a duet, but part of a chamber orchestra. Individually the manakin’s “regular” feathers didn’t resonate like the special ones. But when the nine feathers closest to the special feathers were still attached to the ligaments, they vibrated at around 1500 hertz, harmonized with the club feathers, and amplified the volume of the sound.

  The results, Bostwick said, could lead to better understanding of the newly discovered form of bird communication. “Lots of birds make simple clapping sounds or whooshing noises with their wings, and we haven’t even begun to understand how the sounds are made or how they’ve evolved,” she added.

  TRUTH:

  THE WAY A CLUB-WINGED MANAKIN RUBS ITS FEATHERS BACK AND FORTH TO CREATE SOUND IS SIMILAR TO HOW CRICKETS MAKE CHIRPING NOISES.

  MAGNET-O-VISION

  Birds Can “See” Earth’s Magnetic Field

  To find north, humans look to a compass. But birds may just need to open their eyes, a new study says.

  A bird’s view of the world may include more than just sweeping vistas and grand landscapes. A new study indicates that it might just include Earth’s magnetic field.

  Scientists already suspected birds’ eyes contain molecules that are thought to sense Earth’s magnetic field, but not to actually see it.