BMC Ecology via Wikimedia Commons // CC BY 2.0
BMC Ecology via Wikimedia Commons // CC BY 2.0

This Crab's Secret to a Happy Relationship Is a Turtle's Butt

BMC Ecology via Wikimedia Commons // CC BY 2.0
BMC Ecology via Wikimedia Commons // CC BY 2.0

Columbus crabs (Planes minutus) are tiny and can’t swim very far, but they manage to get around—in more ways than one. They make their homes on anything that floats—logs, ship hulls, plastic junk, and even sea turtles—and ride the waves around. On many of these mobile “islands,” the crabs are plentiful and have an “inclusive” mating system, say biologists Joseph Pfaller and Michael Gil. Sometimes, the crabs like to play the field, readily switching among multiple mating partners. At other times, though, they have more monogamous love lives, sharing their territory with just one other crab, with whom they form a mating pair. The difference? The size of the place where they shack up, say the researchers. They recently published their findings on the crabs' love life in Biology Letters.

Pfaller and Gil were curious about what made the crabs switch between these two mating styles. What was it about a particular turtle or piece of debris that pushed them toward swinging, or into settling down? For many crustaceans that live on or in other animals, it’s the size of the host that dictates how many critters call it home and how they mate. The biologists wondered if the same was true for Columbus crabs, who thrive in both living and non-living “hosts.”

To find out, they took a boat out into the North Pacific Subtropical Gyre—site of the Great Pacific Garbage Patch—and collected dozens of pieces of plastic debris, from soda bottles to boat bumpers. Back in the lab, they measured the size of the debris and recorded the number of crabs, and each crab’s life stage (adult or juvenile) and sex. To get data on sea turtles, they dove into scientific journals instead of the ocean, reading through 270 records of sea turtle–Columbus crab associations, and recording the same information they did with the debris.

Pfaller and Gil found that even though Columbus crabs can travel far and wide on a hunk of plastic or a sea turtle, they still seek out the cozy confines of a burrow-like refuge on their floating homes. On pieces of debris, they usually take up residence in stalks of barnacles. On sea turtles, the crabs tuck themselves into the supracaudal space—the small area between a turtle’s tail and shell. The researchers say that it’s the size of these refuges, and not the overall size of the host, that matters most when it comes to the size and demographics of a crab community—and thus how they mate.

Bigger refuges, of course, support more crabs. A bigger space with more neighbors makes it harder for any one crab to defend a chunk of real estate or a mate, so they opt for a more open and free mating system. A smaller refuge, on the other hand, can only hold so many crabs and is easier to monopolize, leading the crabs to form monogamous pairs and fend off rivals. This was almost always the case for crabs living on sea turtles, where Pfaller and Gil found lone male–female pairs far more frequently than expected by chance. Because a typical turtle’s supracaudal space is the perfect size for two crabs, the researchers say, “sea turtle symbiosis specifically promotes social monogamy.” Who would have thought that living on a turtle’s tush could provide the key to a happy, stable relationship?

Big Questions
Why Do Canada Geese Fly at Night?

Why do Canadian geese fly at night?

Stefan Pociask:

There are actually very good reasons that these geese fly at night, and I will go over them with you. But first ... I must point out that any goose you see that is carrying a valid passport from the great country of Canada, may be called a Canadian Goose. All others should be referred to by their actual name, which is Canada Goose, or Branta canadensis, if you prefer.

I can’t count how many nights at 10 p.m., at midnight, at 3 a.m., and any and all other hours of the night, I have had that all too familiar “Honk! honk-honk-honk HONKhonk HONK HONKhonkhonkhonk HONK honk HOOOONK!” cacophony pass right outside my bedroom window, as the familiar flying-V formations of Canada geese fly over my home.

Those V formations are quite extraordinary. You can’t tell from the ground, but the lead goose is the lowest of the bunch. Each goose behind is slightly higher than the one in front of it, all the way to the last goose, which is flying the highest. They do this because of the aerodynamics of their wings. The only goose that is using all its wing power is the lead goose—point-man, so to speak. When that goose flaps its wings, it causes a certain turbulence of the air that’s following the wing. The next goose in line benefits from this swirling air, and doesn’t need to apply 100 percent of its wingpower. The next goose again benefits from that one, and so on down the line. Flying in formation this way adds 71 percent more distance that they can fly, than when flying alone.

So who gets chosen to be point-man? You’d think the one with the map! Or ... the leader? Or the new guy? No. None of these. They actually take turns. When one gets tired, he will drop back so he can rest a bit and benefit from another goose’s turbulence. When migrating ... in good weather ... with favorable winds, a strong tail wind ... these guys can make up to 1500 miles in a single day ... Hard to imagine, but it’s been done. They are migration masters.

So … the flying at night thing … I’ve already touched upon one of the reasons they prefer the night. It has to do with that turbulence I just mentioned.

You see ... many other large birds (and these are large birds) use thermals to gain altitude and to soar on. Raptors do this. Hawks, eagles, etc. During the day, the landscape is riddled with all kinds of thermals rising from the ground, all depending on what the surface looks like below; how much heat was absorbed and stored from the sun; if it’s dark or light … or even water. These thermals are great for raptors—lots of vertical air movement, all over. But geese don’t soar, and they don’t have need to fly in circles. They have somewhere to go. And all those daytime thermals are a pain in the butt; doesn’t make for smooth sailing. Plus, they interfere with the aforementioned wing turbulence that they use to keep from tiring. At night, several hours after sunset, the Earth cools and those pesky vertical thermals disperse.

So that’s one reason they like the night. Another reason for night flight is to prevent overheating (makes sense, right?). Nights are cooler, so birds that expend a lot of energy with constant flapping (as opposed to soaring) take advantage of the cool of the night.

A third reason is also something I’ve already mentioned. Hawks! And eagles! And falcons! All those guys are diurnal hunters, meaning they hunt during the day. Which goose in its right mind would want to share the not-so-friendly skies with something called a raptor? Now, if you’ve ever seen flocks of geese on the ground and tried to get amongst them or feed them or something … you may already know how mean and nasty they can get. People have used geese instead of watchdogs. They are tough! Especially on the ground. But falcons, hawks, and eagles, hitting them from the air often spells doom. In other words ... their goose is cooked. During the day, they often rest and feed and rejuvenate in the water, where they are safe from raptor attack. As long as they stay in the water.

So given the choice, they take the red-eye.

Otherwise, this can happen ... (WARNING: Extremely dramatic footage follows of a falcon/goose battle. Also extremely exciting! Who will win?!)

You’ll certainly see Canada geese fly during the day. But the smart goose prefers the night.

All migratory birds are split up into three classes, regarding migration habits. Nocturnal Migrants, are the first classification, [and they fly] at night. This would include most of the seed-eating songbirds, such as sparrows and thrushes. They will fly all night, then rest up, top off the tank with food, and try to stay out of sight of raptors during the day.

The second group is the Diurnal Migrants, who migrate during the day. These are often the insect-eaters; jays, swifts, swallows, larks, etc. They benefit greatly from the daytime thermals during their journey—not for reasons of soaring, like raptors use thermals, but rather because these warm updrafts send up clouds of insects from the fields, right into the paths of the migrating birds, like a food delivery service. Most insects are so light that a gust of wind or a thermal current can lift them high into the air—and unwittingly into the beak of a hungry swallow.

And the third class of [migratory birds] are those that have a preference, but actually migrate day and/or night, depending on the circumstances. Canada geese, and many waterfowl, fit into this last category.

This post originally appeared on Quora. Click here to view.

25 Icy-Cool Facts About Polar Bears

From starring in Coca-Cola ads to becoming the poster child for climate change, the polar bear is quite the high-profile species. Ursus maritimus is a fascinating animal that roams across the Arctic Circle through Norway, Russia, Canada, Greenland, and Alaska, and there's more to them than the adorable faces you see in children's books and advertisements. Here are 25 facts you should know about the polar bear:


A polar bear walks across the snow at sunset.

Polar bears can weigh more than 1300 pounds and span more than 8 feet, 6 inches from nose to tail, making them the largest carnivores to currently walk the Earth. (Though other bears can grow larger, like Alaska's 10-foot-long Kodiak bear, they're omnivorous, while polar bears prefer an all-meat diet.) The males far outweigh their female counterparts, who may only weigh between 330 and 650 pounds. In general, though, a bear's weight fluctuates significantly throughout the year, with some bears packing on 50 percent more body weight over the course of a successful hunting season, then losing it over the course of their long fasting months.


A shot from below of two polar bears swimming in clear blue water

Because they spend so much of their lives on ice, rather than land, polar bears are the only bears to be considered marine mammals. They hunt, court, and mate out on the ice, spending many months of the year far from land.


A large polar bear opens its mouth in a roar.

Human beings aren't as high on the global food chain as you might think. Polar bears don't have any natural predators, and their intensely carnivorous diet puts them at the top of the food chain with species like killer whales, according to researchers, while humans fall somewhere closer to the middle. Don't worry too much about getting eaten by one, though—a 2017 study found that during the past 144 years, there have only been 20 fatal polar bear attacks in all of the five countries that have polar bear populations. However, as food becomes more scarce for the bears, humans living in polar territory may soon face more risk from starving bears.


A polar bear walks across a large field of ice.

Other than the two to three years a cub spends with its mother, polar bears are pretty much solitary creatures. Adults spend only a few days a year mating, then go on their own way, spreading out to hunt on their own. They rely on the scent left by the sweat glands on their paws to track other bears, using the smell to sense where potential mates might be headed, among other things.


A polar bear sleeps cuddled next to her cub.
Paul J. Richards, AFP/Getty Images

Polar bears can play nice with each other sometimes. On occasion, they will hang out together in large groups, especially if there's a big meal that multiple bears can take part in, like a whale carcass. When they do spend time together (in what's called a sleuth), male bears will play-fight with each other, wrestling and swatting at each other without doing any real harm. According to the documentary Polar Bears: Spy on the Ice, polar bears can recognize friends they've met before even if they go without seeing each other for many years.


A polar bear shares food with a cub.

When food is plentiful, polar bears are very selective about what they eat. They hunt seals, but if there are plenty available to hunt, they won't eat their whole catch. Instead, they'll only eat the energy-rich blubber (up to 100 pounds at a time), leaving the rest of the carcass for other animals to scavenge. When hunting is good, their diet is made up of about 90 to 95 percent fat. When times are lean, though, they'll happily branch out, eating reindeer, rodents, eggs, seaweed, and anything else they can get their claws on. However, because their bodies are so much better at digesting fat than protein, researchers think that if Arctic ice continues to melt and polar bears become unable access the ice (with its blubber-rich seals), they won't be able to get enough calories on land to survive [PDF].


A polar bear sprawls out on its stomach.

When they're not out on the ice scoping out seals, polar bears spend an incredible amount of time fasting. The female polar bears fast longer than any other mammal species—in Canada's Hudson Bay, pregnant polar bears can fast up to 240 days, or almost eight months. There's reason to think they'll be fasting even longer in the future as sea ice melts, leaving bears with fewer hunting opportunities and less time to accumulate the fat stores needed to get through the lean months. During the 1980s, non-pregnant polar bears spent 120 days fasting between hunting seasons, but researchers now think that the bears will have to go without food longer and longer, fasting for as much as 180 days at a time in the future.


Two polar bears walk through the snow.

The average bear might travel across 100,000 square miles in its lifetime, and that number may be getting higher. In 2013, a bear searcher told the BBC that polar bears were spending 9 to 13 percent more time being active to make up for the fact that the ice they hunt on is drifting faster, leaving them walking on a "treadmill" just to stay within their territory. One bear tracked by the WWF traveled almost 2300 miles from Norway to Russia in less than a year. Due to receding ice, polar bears have to walk farther to find prey, wasting valuable energy. The energy they gain from eating a single ringed seal might not even make up for what they expend trying to find and catch it.


A polar bear swims toward the camera.

Polar bears are savvy swimmers, paddling at an average speed of 6 miles per hour. And it's a good thing: Due to all that melting ice, polar bears are putting their swimming skills to lengthy use. In 2011, a study reported that a tagged female polar bear swam a total of 426 miles in one nine-day stretch across the Beaufort Sea above Alaska, losing 22 percent of her body weight in the process. Another bear in the study swam for 12 days, though she at least stopped to take some breaks.


A wet polar bear sticks its tongue out.

You'd think with all that plunging in Arctic waters, polar bears might get chilly occasionally. But since they're built to withstand extreme cold on a regular basis, they actually have the opposite problem: They overheat very easily, and are more likely to die from the heat than the cold. Their two layers of fur and solid layer of body fat (up to 4.5 inches thick) keep their metabolic rate consistent when temperatures reach as low as -34° F. They can sprint up to 30 miles per hour if need be, but much like you wouldn't want to run a race in a heavy ski jacket, polar bears can't spend much time chasing after their prey lest they overheat—a bear's body temperature can rise to feverish temps if they move too fast. On land, they typically only walk at speeds of three miles an hour, and their main hunting technique involves staying very still for hours or days at a time, waiting for a seal to emerge from the ice to breathe.


A polar bear sits with her two cubs.

In addition to changing their travel patterns and dinner prospects, climate change is altering polar bears' love lives. As the ice-traversing bears are forced to spend more time on the tundra, their habitats are starting to overlap with those of grizzly bears. In some places, the two species are getting more comfortable with each other, with amorous results. In Alaska and western Canada, grizzlies and polar bears are doing more cross-breeding, creating hybrid offspring.


A polar bear cub sits on its mother's back.

At birth, polar bears weigh anywhere from 16 to 24 ounces—about what a guinea pig does. As newborns, they're blind, toothless, and only about a foot long. But by the time they emerge from their den for the first time around four months later, they are substantially larger, weighing between 22 and 33 pounds. In addition to nursing, they'll begin eating solid food around that time, and by 8 months old, they'll weigh 100 pounds or more.


A polar bear swipes its paws in the water.

In order to balance on ice, polar bears boast giant feet. Their paws can measure up to 12 inches in diameter, acting like snowshoes to spread out their weight on thin ice and deep snow. The bumpy papillae (like the ones on your tongue) on their footpads help grip the ice, keeping them from sliding around. They also have long, curved claws that can measure almost 4 inches—all the better to grab onto slippery seals.


A polar bear leaps into the water.

While black bears, grizzlies, and other bear species spend each winter denning, forgoing eating, drinking, moving, pooping, and peeing for months on end, polar bears stay active all winter. Polar bears don't need to sleep through the winter, though, because there's plenty of food available to them in the coldest months, when they take to the sea ice to hunt for seals. The only exception is during pregnancy, when a female polar bear digs herself a den and remains sealed inside, surviving off her stores of fat, until her cubs grow large enough to survive outdoors.


Two polar bears sleep covered in snow.

Polar bears may not hibernate, but they are happy to lay low when bad weather hits. During the winter, they dig themselves into shallow pits in the snow to protect themselves from wind, sometimes remaining there for days as the snow piles up on top of them like a warm blanket. Sometimes, they take a similar approach to staying cool, digging through the tundra down to the permafrost during the summer to keep from overheating.


A polar bear wears a tracking collar.
Paul J. Richards, AFP/Getty Images

Considering how far they travel—both walking and swimming—over a given year, you can imagine how hard it is for scientists to track polar bears. By nature, they spend a huge amount of time alone in remote locations. Scientists use boats, helicopters, and low-flying planes to observe them, but that only works in good weather and in certain locations. So recently, they've turned to satellites, fitting bears with non-invasive radio collars and tracking them through high-resolution satellite imagery. It's cheaper than sending out a helicopter, and it lets researchers identify bears even in the most remote areas of the Arctic.


A swimming polar bear peeks its nose out of the water.

Polar bears don't have to worry about getting water up their nose. When they swim, their nostrils close to prevent them from breathing in water. They can swim at depths up to 15 feet, and while they typically only dive for a few seconds, they can hold their breath for more than two minutes, enabling them to sneak up on seals resting on ice floes. In 2015, scientists reported observing a record-breaking polar bear dive that totaled 3 minutes and 10 seconds. The hungry bear stalked three seals from afar, swimming almost 150 feet underwater without surfacing for a breath or to reorient himself to the seals' location before bursting out of the water where one of the seals was resting. (Sadly, his prey got away.)


A polar bear in a zoo swims with a ball.
Ina Fassbender, AFP/Getty Images

Though polar bears are sometimes known as the white bear, they aren't white. Their hair is colorless and hollow, and only appears white because of the way light scatters through their fur. (Under that mass of hair, their skin is as black as their noses.) When bears are subject to warmer temperatures in captivity, though, they can take on a bit of a verdant hue. Algae infestations can turn polar bears green, and not just on the outer layer of their fur. The colorful algae grows inside the hollow tube of each hair. This green growth thrives in humid climates, like Singapore, where the bears don't naturally live.


A Bulgarian stamp set featuring a polar bear, a seal, penguins, and a walrus.
State Agency for Information Technology and Communications of Bulgaria, Wikimedia Commons // CC BY 2.5

Though you might see polar bears and penguins together in Coca-Cola ads or on winter-themed pajamas, the two species never mix in real life. They live at opposite ends of the Earth, though they both spend their days in icy waters. Polar bears exclusively inhabit the Arctic, and penguins only live in the Southern Hemisphere. The closest they ever get is when they live in the same zoo.


Gold glitter on a black background

At the Assiniboine Park Zoo in Winnipeg, Canada, the polar bears have sparkly poop. In 2014, zookeepers began feeding each of their bears a different color of non-toxic glitter so that they could trace their bowel movements, analyzing the samples to identify health issues, track stress hormones, and generally see how the bears are dealing with zoo life. The colors help the zookeepers label which poop comes from which bear.


A 1938, black-and-white photo of a polar bear lying on its back in a zoo
Topical Press Agency/Getty Images

Captive polar bears have piqued public curiosity since as early as the Middle Ages, when the bears were occasionally given to European royalty by Viking traders. In the 1200s, when Henry III kept one in London, it was muzzled and chained but allowed to catch fish and swim in the Thames River. In the 17th century, Frederick I of Prussia kept a defanged and declawed polar bear, staging public fights between it and other large mammals for public amusement.


The orange cover of 'Teddybär' shows a person in a polar bear suit with his arms wrapped around a smiling boy.

In the early 20th century, getting a picture with a man dressed in a polar bear suit was a fairly standard activity in Germany, at least according to the many photos found by French photo collector Jeann-Marie Donat. Donat spent 20 years tracking down the vintage photos, taken between 1920 and 1960, for his 2016 book Teddybär. There are several potential explanations for why so many Germans elected to stop for photos with people in polar bear suits (or to dress up as polar bears themselves). Donat suggests that it might trace back to the popularity of the two polar bears that arrived at the Berlin Zoo in the 1920s, while Hyperallergic notes that the costume was created as a Fanta advertising stunt, designed to distract Germans from the horrors of World War II. The photos show people young and old posing next to bears at the beach, in parks, in the street, in the summer and winter, alone and in groups. They all look delighted to get a chance at a polar-bear souvenir.


Knut and his handler pose for photos lying down on their bellies.
John Macdougall, AFP/Getty Images

Knut, a polar bear cub born at the Berlin Zoological Garden in 2006, was hand-raised by zookeepers after being abandoned by his mother at birth. The cute cub became an instant tourist attraction—the most famous bear in the world, even—and the zoo's attendance rates skyrocketed, netting an extra $1.35 million in tickets when the bear began making twice-a-day public appearances.

But not everyone was psyched about "Knutmania." The young bear's popularity proved to be controversial for animal rights organizations like PETA, whose German spokesperson Frank Albrecht said the zoo should have let the orphaned Knut die rather than continue hand-feeding him, a process that he called a "gross violation of animal protection laws." In 2007, the bear received an anonymous, handwritten death threat from a hater who simply wrote "Knut is dead! Thursday midday." The zoo took the fax seriously enough to assign triple the amount of zookeepers keeping watch over the polar bear during his daily public romp. (Knut continued to live at the Berlin zoo until his death at age 4 from an autoimmune disease.)


Photographers crowd in front of a barrier to photograph Knut at a zoo.
John Macdougall, AFP/Getty Images

In 2007, celebrity photographer Annie Leibovitz photographed Knut for the cover of Vanity Fair's annual "Green" issue. While Knut appeared solo on the cover of the German edition, he was Photoshopped into an image with Leonardo DiCaprio for the American edition. After his death, the Berlin zoo erected a bronze statue in his honor, and his body was preserved for display at the city’s natural history museum.


A green sign in a snowy field reads 'Polar Bear Alert: Stop.'
Paul J. Richards, AFP/Getty Images

Churchill, a town in Manitoba, Canada on the shores of the Hudson Bay, is known as the polar bear capital of the world. During the fall, hundreds of polar bears pass through on their way to their icy hunting grounds on the bay, waiting nearby as the ice hardens for the winter. The locals have adopted unique ways of living with the hungry bears. Many don't lock their doors, so that if someone is running away from a polar bear, they can duck into any doorway. Since Halloween falls right in the middle of polar bear season in town, city employees, police officers, volunteer fire officials, and polar bear conservationists stay on patrol to drive away any bears that might be tempted to go trick-or-treating themselves, using helicopters, sirens, air horns, rubber bullets, and more to keep the bears at bay. Kids, for their part, aren't allowed to wear anything white for the evening.

Churchill also runs a "polar bear jail" for bears that continue to wander into town. Residents are encouraged to call the Polar Bear Alert Program hotline year-round if they see a bear in town, and conservation officers will come and try to scare it away. If shooting loud scare rounds at the bear doesn't do the trick, they trap the bear, or, if all else fails, hit it with a tranquilizer dart and take it to the Polar Bear Holding Facility. The specially-designed compound can hold up to 30 bears and is meant to keep bears that are aggressive or persistently return to the community. When the bay freezes, these bears are transported by helicopter or vehicle onto the ice, where they resume their normal winter hunting routine. With warmer temperatures keeping bears off the ice for longer and longer periods, more towns may soon have to learn from Churchill's strategies for peaceful coexistence.


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