Turtle Moms Choose Their Babies' Genders by Where They Build Their Nests

If turtles had realtors, their motto would also be "Location, location, location!"—but not because they care about a scenic vista. The spot a mother turtle chooses to dig her nest determines whether her young will be males or females. This might even be the most important factor in her decision.

A female painted turtle (Chrysemys picta) is not an over-involved parent. She digs a hole in the dirt, lays a batch of eggs there, and buries them. Then she returns to her freshwater life without giving the nest another thought. The eggs incubate and develop under the soil while the summer wears on. Hatchlings finally chip their way free in the late summer or early fall, but in cooler parts of North America they don't leave the nest right away; they stay hunkered down with their siblings to hibernate until the following spring.

Sometime in the middle of the summer, a significant event happens inside each buried egg: the developing turtle becomes male or female. Its sex hasn't been determined by its genes like ours is. Instead, as with many other reptiles, the temperature in the nest tilts the egg toward one sex or the other. Cooler nests produce males and warmer ones make females. If the nest stays within a narrow temperature range, hatchlings of both sexes will crawl out at the end of the season.

Timothy Mitchell, a Ph.D. student in ecology at Iowa State University, studies a population of painted turtles living in northwestern Illinois. These particular turtles have been under close watch by scientists for more than two decades, but it hasn't become clear whether turtle moms are active in determining their hatchlings' sex—do they choose nest sites that will best balance the sex ratio of their eggs? To find out, Mitchell set up a kind of nest-building competition between himself and the mother reptiles.

Mitchell scoped out 20 nests in his study site, a forested area near the Mississippi River. Right after the mothers left their nests behind, he went in and dug the eggs up. Then he tucked the eggs into artificial, Styrofoam-box nests. Half the eggs from each batch went into a box right next to where their mother had left them, buried at the same depth to create a controlled replica of the original nest. The other half went into a box at a site Mitchell selected at random.

(How do you randomly place a turtle nest? Mitchell used a random number generator to choose a distance away from the original nest, up to 30 meters. Then he flung a pencil in the air and walked in whatever direction in was pointing when it fell. If the resulting location was, say, in the Mississippi, he tried again.)

Just before they were due to hatch, the eggs were dug up and brought to a lab. Mitchell monitored their hatching and then returned the tiny turtles to their artificial nests for hibernation (along with a sprinkling of eggshells, as if the turtles had been there the whole time). He checked on the baby turtles once more in the spring.

Temperature sensors hidden in the nests revealed that sites chosen by turtle moms were a little warmer than Mitchell's randomly selected ones. This meant they were more open to the sun; nests that were shaded by vegetation were cooler.

Between the original nest sites and the random ones, there was no difference in the number of eggs that survived all the way through hatching and hibernation. But there was a major difference in sex ratio: while the turtle moms' nest sites produced roughly equal numbers of boy and girl turtles, the hatchlings from Mitchell's randomly placed nests were about 80 percent male.

"This strongly suggests this process of sex ratio selection is influencing where Mom chooses to nest," Mitchell says, "as opposed to selection to have eggs survive."

Wherever she builds her nest within this forest, a painted turtle mother can be assured that her young will survive equally well. But it's in her best interest to keep the sex ratio balanced. In the long term, turtles that tend to build male-heavy or female-heavy nests will lose out when the population swings in that direction, because young turtles of the opposite sex will then have better mating prospects.

A warming climate is a threat to any species whose sex ratios depend on the temperature. But if female turtles are savvy enough to leave their eggs in exactly the right sex-balancing spot, should we stop worrying about them? "That is still the big question in the field!" Mitchell says. He thinks moms' choice of nest sites will be a crucial part of how this species responds to climate change. But many other factors will matter too, like the fragmentation of the turtles' habitat and how the climate affects their predators. Turtle moms today know how to build a perfect nest for their offspring , but that balance may be as fragile as eggshells.


Image: Timothy Mitchell.

Timothy S. Mitchell, Jessica A. Maciel, & Fredric J. Janzen (2013). Does sex-ratio selection influence nest-site choice in a reptile with temperature-dependent sex determination? Proceedings of the Royal Society B DOI: 10.1098/rspb.2013.2460

Cooler Than Your Environmental Club: An Interview with My Little Sister about the Adirondack Youth Climate Summit

Teenagers who want to cause a disruption don't have to ride a skateboard anymore; these days they can do it on a bike generator. Earlier this November a crowd of students came together in Upstate New York to share ideas about greening their schools and addressing climate change on a small and large scale.  My youngest sister, Leigh, is a senior in high school and was at the conference for her second year. I asked her what they did there, and she told me about energy efficiency, celeriac soup, and how her generation is going to do things differently. (I never did get a straight answer about some Facebook photos, though.)

*****************

Hi Leigh! So who attends the Adirondack Youth Climate Summit?

There were about 150 students representing 27 colleges and high schools around New York, mostly from the Adirondack region. Each school could send 5 to 6 students along with a teacher chaperone. Students at my school had to write an essay explaining why they wanted to go to the summit and what interest they had in climate change. (Most students I talked to were shocked that my school had been so selective because their schools just brought their entire environmental club.)

By the way, I hope email is OK. Would I have more generational cred with you right now if I were conducting this interview via SnapChat or something?

I have to say, I much prefer the transfer of information through text bubbles containing less than 140 characters attached to a picture I can only view for 10 seconds on a 4-inch screen...but I guess this will do.

What kinds of workshops did you go to?

I got to attend three different workshops of my choice on the first day, splitting up with my school group so that we could cover more ground. I attended the three that were geared towards successfully sustaining a school garden and implementing younger students into climate action, because that's what I've been focused on at school the past couple years. The rest of my team attended workshops about composting, green teams, energy efficiency, biofuels, and recycling.

I hear the food was a highlight.

The food was absolutely delicious! All the meals and snacks were provided by local farms and vendors. They had vegetarian, vegan and gluten-free options, and Ben & Jerry's (a major sponsor of the summit) provided ice cream the second day. I caught myself enjoying kale chips and even tried parsnip and celeriac for the first time in a delicious soup that a Culinary Arts professor from Paul Smith's College made. (See recipe below.)

As weird as it sounds, I think the presence of wholesome, fresh, unprocessed food really boosted everyone's brain power for a few days.

And there were speakers too?

Brian Stillwell of Alliance for Climate Education kicked off the summit with a catchy, motivating presentation about climate change and the science behind it, followed by Brother Yusef Burgess of Youth Ed-Venture and the Children & Nature Network, who spoke about using the power of nature to transform and educate youth. Later in the afternoon Dr. Susan Powers, the Associate Director for Sustainability at Clarkson University, presented to us the outcomes of climate change in both our best and worst case scenarios.

Mark and Kristin Kimball, who own Essex Farm in the Adirondacks, hosted the dance party, fed us freshly harvested carrots, and encouraged our generation to be the driving force of the climate movement—and, more importantly, to have fun doing it. They made the point that these days, things like smoking cigarettes or dumping gasoline into a lake are considered "socially unacceptable," but that took time. Now, it is our time to make not caring about the environment be socially unacceptable.

Was it valuable just interacting with the other kids there, from different kinds of schools? Were you learning and getting ideas from each other?

YES. The second day, there was a 2-hour poster session where all the schools displayed posters of their current "green" efforts and plans for the future. I had a chance to talk to so many different schools and share ideas about outdoors clubs, gardening problems, recycling efforts and cafeteria food. I had conversations with a high school that was having trouble even starting an environmental club due to the lack of support from administration, and on the other end of the spectrum, I talked to a school that had livestock and taught all their science classes on a farm.

We also had the amazing opportunity to Skype with Finland, where they were holding a similar youth climate summit modeled after ours in the Adirondacks. Despite the sound lag and language barrier, it was still inspiring to see that kids our age halfway around the globe are facing the same problems we are.

It looks like you guys had a lot of fun at this dance party. In your Facebook photos I observed electric guitar, someone crowdsurfing, a guy in a sailor hat juggling fire, and what appeared to be people using ropes to move a large rock. Are these the elements of a good party for the young environmentalist crowd?

I think these are the elements of any good party, actually. Moving the rock could have been a metaphor for how teamwork can move the world or something, but it was really just for the fun of moving a rock. We were told that our generation will make it through this difficult time in climate change only if we have fun in the process.

What sorts of ideas or projects did you bring back from the summit to use at school?

The second day of the summit, all the teams were given 2 hours to create their school's "Climate Action Plan" and a detailed timeline to present to the rest of the schools at the end of the day. Our team decided to focus on 4 major projects in the coming year: improving the school garden, building a bike generator for the lobby, holding a bi-annual school-wide locker clean-out to donate gently used school supplies and teach proper recycling, and finding places to cut the school's phantom energy usage (a.k.a. the wattage used by electronics when they're turned off but still plugged in).

You may not know this, but back when I was at your school I belonged to an "environmental club" too. This meant that a couple of us would go to all the classrooms after school and pull trash out of the blue bins, because otherwise the maintenance guys refused to recycle. Is it fair to say things have come a long way?

Simply put, yes. We have a recycling bin in every classroom, our cafeteria serves vegetables from a number of local farms, quarterly grades and comments are now only available online, our drinking fountains are now water-bottle filling stations, and we have a garden that brings vegetables to the salad bar. We have solar panels on one building and another LEED-qualified building, with another one in the construction phase.

I think we're also a little cooler than your environmental club, because now we are the "Green Avengers," equipped with a logo and a Facebook page.

Are you optimistic about climate change? Do you come back from an event like this feeling like you're part of a group of people who will actually make a difference, whether it's through school-level projects now, or after college as policy makers? Or are we pretty much screwed?

Both times going to the summit I came back incredibly high in motivation, but I knew if I didn't write down all my ideas and get acting quickly, I would lose my energy. Spending time around so many like-minded people definitely makes me excited to get out there and make change.

It also reminds me we have to be able to work on our own and not rely on the work of others because that's part of the attitude that brought us to this predicament in the first place. As Dr. Powers told us, even in the earth's "best-case scenario," we'll still experience rising global temperatures. It's just up to my generation to slow the acceleration of carbon dioxide emissions and provide the optimistic attitude.

Celeriac and Parsnip Soup
Yields 18-24 servings (reduce if you're not feeding a youth summit)

Ingredients:
5 pounds cubed celeriac root
5 pounds chopped parsnip
6 tablespoons olive oil
15 cups vegetable stock
1 bundle thyme
1/2 teaspoon salt
1/2 teaspoon ground black pepper

Preparation:
Preheat the over to 400°F. Toss the celeriac and parsnip with the olive oil. Arrange the vegetables in a single layer on a foil-covered baking sheet. Roast them 35-45 minutes, flipping once, until they are tender and golden brown. Combine the caramelized vegetables with the stock and other ingredients in a pot over medium-high heat. After bringing to a boil, let the soup simmer for 15 minutes. Put all the food through a blender or food processor until smooth and serve hot.

Images: The Wild Center (top); Leigh Preston (bottom).

Why a Lost Baby Seal May Soon Be at Your Doorstep

Every host knows when you run out of ice, the party's over. For young seals surviving on ice floes, the festivities are breaking up sooner than they used to. That sends vulnerable youngsters into the ocean before they're ready—maybe to end up stranded on a beach near you.

To keep their young from becoming drifting bait in a predator-filled ocean, female harp seals give birth on top of winter sea ice. The pups stay on the ice, undercover in a coat of white fur, until they're old enough to survive in the ocean. Then they shed their white coats, dive in, and begin migrating with the rest of their population.

Harp seals live in two main populations, one on either side of the northern Atlantic. From the population on this side of the pond, increasing numbers of seals have been showing up stranded along the U.S. coast, from Maine all the way down to North Carolina. Researchers at Duke University looked for patterns in these strandings—more than 3,000 over the past two decades.

Not too surprisingly, there was a clear relationship between strandings and the amount of sea ice. Years with more ice had fewer strandings. In years with less ice, when melting floes might force pups into the water before they're ready, strandings went up.

The same trend didn't apply to adults, however. Strandings of adult harp seals weren't linked to the amount of sea ice in that year. But in all years, the majority of stranded seals were pups. That means fluctuations in sea ice have the strongest effect on young harp seals.

The researchers also saw that males were more likely to strand than females. This may be due to what they call a "tendency to wander" among males. Brianne Soulen, one of the paper's lead authors, adds that because adult females need to spend more energy on things like pregnancy, they're less likely to stray from safe feeding grounds.

Genetic factors may also be at work. Soulen says they found slightly less genetic diversity among males, which in theory could make them more susceptible to disease or other factors. No matter the reason, if a harp seal does wind up on the shore of your local beach, it's likely to be a baby boy. Get blue balloons.

In the most recent years included in the study, 2009 and 2010, the usual pattern didn't hold up. The year 2010 was bad for ice, but didn't have a lot of strandings. However, Soulen doesn't see this as reason for optimism. An earlier study saw harp seals changing their migratory behavior in response to shifting ice cover; they may simply be stranding someplace else now, where they're not counted. Or the population as a whole may have dropped dramatically.

It matters, of course, because the ice is running out everywhere. Despite year-to-year fluctuation, the authors write, ice cover in the North Atlantic is disappearing at up to 6% per decade. And Soulen says what's happening with the harp seals provides a big hint about the state of other marine mammals. "Harp seals are a good representative species of the effects of ice changes." The hooded seal population in the western North Atlantic, for example, has declined by 90% since the 1940s, as ice there has steadily disappeared.

When sea ice is gone, there's no one who can dash out for more. The party may not be over quite yet, but it's getting pretty lame.


Image: courtesy of the International Fund for Animal Welfare

Brianne K. Soulen, Kristina Cammen, Thomas F. Schultz, & David W. Johnston (2013). Factors Affecting Harp Seal (Pagophilus groenlandicus) Strandings in the Northwest Atlantic PLOS ONE DOI: 10.1371/journal.pone.0068779

Google Promises We'll Feel Better in the Summer

Shakespeare wasn't kidding about the "winter of our discontent." In the colder and darker months, people do more internet searches for mental health terms, from anxiety and ADHD all the way to suicide. Search patterns also promise that like a refreshed browser window, better times are due to arrive soon.

John Ayers, of the Center for Behavioral Epidemiology and Community Health in San Diego, and other researchers dove into Google Trends to explore whether certain searches vary by season. "Seasonal affective disorder is one of the most studied phenomena in mental health," Ayers says, "with many individuals suffering mood changes from summer to winter due to changes in solar intensity." He wanted to find out whether any other mental health complaints changed with the seasons, as some studies had hinted.

Since Google Trends breaks down searches by category, the researchers started in the "mental health" section. Looking at all mental health searches in the United States between 2006 and 2011, they saw a consistent cycle with peaks in the winter and troughs in the summer. (If you do this search yourself, you'll see that there's also a dip around the December holidays—but the curve reliably bottoms out in July of each year.)

The team did some statistical smoothing and found that mental health searches overall were about 14% higher in the winter than in the summer. To confirm that the difference was due to the season, they ran the same analysis on data from Australia. Searches cycled in the same way—about 11%  higher in winter than summer—but the peaks in the southern-hemisphere country were almost exactly 6 months out of sync with the United States.

When the scientists broke down searches by specific symptoms or illnesses, the seasonal cycle remained—and in some cases got much stronger. "We were very surprised" to see this, Ayers says. Searches including the terms ADHD, anxiety, bipolar, depression, anorexia or bulimia, OCD, schizophrenia, and suicide all rose in the winter and fell in the summer.

One of the most dramatically cycling search terms was schizophrenia, at 37% higher in the winter. Eating disorder terms varied just as strongly. (The smallest seasonal difference was for anxiety, which was just 7% higher in the winter in the United States, and 15% in Australia.)

Some of this seasonality might be due to the schedule of the school year, Ayers points out. Referrals for kids with ADHD and eating disorders may come from their schools.

Other explanations involve winter itself. The effect of shorter days on our circadian rhythms and hormone levels might be a factor, the authors write, as in seasonal affective disorder. They speculate that a lack of vitamin D (which we make using sunlight) in the winter might contribute. Even omega 3 fatty acids might matter: we consume less of them in winter, and omega 3 deficiency has been linked to some mental illnesses.

There's also the question of what we're doing all season. People hunkered indoors during the colder months may have fewer chances for socializing, which is "a well-known health emollient," the authors write. The same goes for physical activity.

"There is a lot more we need to learn about mental health and seasonality," Ayers says. "For instance, is there a universal mechanism that impacts our mental health?"

Of course, sometimes our malaise isn't about the season.

Whatever portion of mental health is predictable, though, doctors would love to know about it and use that information to help.

This study doesn't reveal much about low-income or elderly populations who aren't online. And knowing what people are searching for isn't exactly the same as knowing what symptoms they're experiencing. "We are actively working to address these limitations," Ayers says. Working with Google.org, the charitable branch of Google, he hopes to develop systems similar to Google Flu Trends that can track a population's mental health.

"Intuition suggests that these results are reflective of an important link between the seasons and mental health," Ayers says. For now, we have the reassurance of computer algorithms that skies will be clearer soon.


Ayers, J., Althouse, B., Allem, J., Rosenquist, J., & Ford, D. (2013). Seasonality in Seeking Mental Health Information on Google American Journal of Preventive Medicine, 44 (5), 520-525 DOI: 10.1016/j.amepre.2013.01.012

Image: Skaneateles, NY, by me.

New Journal Celebrates Animal Stalking

Christmas arrived early this year for people who love animals carrying transmitters around. A new open-access journal called Animal Biotelemetry launched this week, and it promises to bring new tales of mind-blowing bird migrations and seals that study climate change (without exactly having volunteered for the job). Also, sharks.

Published by BioMed Central, the journal will include all kinds of research having to do with biological data gathered by instruments attached to animals. This is a field that's been expanding as the technologies themselves shrink. A few decades ago, scientists were limited to studying the movements of giant land animals such as bears or elk—because transmitters and battery packs were too bulky to comfortably attach to other creatures. Now, miniaturized electronics (aided by GPS satellites) mean that even lightweight birds can carry tracking devices.

Editor A. Peter Klimley describes the history of the field in an introduction to the journal. Klimley himself is a professor and shark guy at the University of California, Davis. His biography claims that he "is known to have held his breath while diving up to 100m deep in order to hand-tag hammerhead sharks with a dart gun." In case "biotelemetry" didn't sound exciting to you.

To mark the occasion, here are some earlier posts involving animals carrying transmitters around, since I am one of the aforementioned people who love them.

Monitoring from Space Shows Even This Giant Crab Can Navigate Better than You

Climate-Studying Seals Bring Back Happy News

This Penguin: An Unexpected Journey


Klimley, A. (2013). Why publish Animal Biotelemetry? Animal Biotelemetry, 1 (1) DOI: 10.1186/2050-3385-1-1

Image: by MEOP Norway North

Bats, like Batman, Thrive in a Post-Apocalyptic Environment

Without plagues, earthquakes, and unhinged criminal masterminds, the residents of Gotham might never need to put up the bat signal. Real bats, of course, are less concerned with responding to emergencies than with eating bugs. But like Batman, they do just fine—if not better than ever—in recently devastated environments. Specifically, forests that have burned down.

For five weeks in the summer of 2002, a wildfire tore through national forests in the Sierra Nevada mountains. The McNally Fire was started by a careless human, and ended with over 150,000 acres burned. A year later, scientists came by to see how the bats were doing.

"Bat ecologists have known for a while now that bats respond favorably to controlled, low intensity fires," says Michael Buchalski of Western Michigan University, one of the study's authors. "We were more interested in the effects of large, natural fires." These blazes can completely destroy the forest canopy, leaving an area unrecognizable.

Researchers visited 14 sites in the woods, half in burned areas and half in areas that were untouched. They left devices that recorded the ultrasonic cries of echolocating bats at night. Since tallying up all the bat activity they heard could be misleading—one flourishing species of bats might mask the disappearance of another—they divided the recordings into groups of similar-sounding calls, representing groups of bat species.

The researchers estimated how plentiful each type of bat was based on how often they heard its calls. Comparing burned and unburned areas, they found that no bat group was bothered by the fire. Instead, every group of bats was at least as plentiful in the fire-scorched areas—and some were doing even better than usual.

Despite the absence of costumed criminals, a few factors might account for bats' increased activity in a scorched landscape. Bats hunt by swooping through the air and searching for insects below. With much of the vegetation cleared out by fire, insects have fewer places to hide, and hunting bats have a clearer view for their echolocation.

Additionally, the first plant regrowth after a fire leads to a boom in insect species. This means there's more prey than ever available for hungry bats. "One-stop shopping!" says coauthor Joseph Fontaine of Murdoch University. Those bats may find new places to roost—or, if you prefer, build their secret lairs—inside dead trees.

Buchalski and Fontaine say bats probably need a mix of landscapes to thrive, including areas that have recently burned. Carefully allowing forests to burn more like they did in the past could lead to "healthier forests and healthier wildlife populations," Buchalski says. "However, this is a very contentious issue within the field of forestry management."

"We have spent the majority of the last century suppressing and excluding fire," Fontaine adds. "More fire right now is probably not a bad thing whatsoever." (For non-human animals, anyway.) With climate change increasing the potential for drought and wildfire, the authors say that understanding how different species deal with fire is becoming more important.

Bats aren't the only animals that appreciate a fire. Fontaine says deer mice and other short-lived rodents respond very well to fire, and deer and elk like to chew on the soft new shrubs that have regrown a few years later. Several types of woodpeckers, he adds, rely on fires. Many bird species that forage in the open and don't need living trees to make their nests have a similar response to the bats.

Although forest fires are a boon for many species, the robin doesn't seem to be among them.


Buchalski, M., Fontaine, J., Heady, P., Hayes, J., & Frick, W. (2013). Bat Response to Differing Fire Severity in Mixed-Conifer Forest California, USA PLoS ONE, 8 (3) DOI: 10.1371/journal.pone.0057884

Image from public domain files at Wikia.

How We Changed Penguins Just by Watching

If a penguin falls in the forest and no one is there to hear it, I don't know what kind of forest that is—but everyone who's interested in penguins is probably hanging out a lot closer to the South Pole. The charismatic birds let scientists and tourists alike get a close look without too much trouble. And all that familiarity has the potential to change penguins, and other closely watched animals, for good.

King penguins (Aptenodytes patagonicus) appeal to zoo visitors and cold-resistant tourists by doing miniature tuxedoed human impressions, and to researchers by diving 100 meters into the ocean or carrying their chicks on their feet to keep warm. In the Crozet Archipelago, an island chain in the far southern Indian Ocean, scientists study the penguins as well as other polar items of interest from a permanent station called Alfred Faure. For 50 years, the camp has shared a small island with a colony of more than 48,000 penguins.

A group of researchers led by Vincent Viblanc from the University of Strasbourg wondered how decades of living near the human research station has affected this population of king penguins. To find out, they studied some penguins that live close to the camp and see humans at least once a day. They compared them to penguins from farther away on the island, where humans visit once a week or less.

The researchers caught 15 penguins from the frequently bothered group, plus 18 more from the group that was mostly left alone. After taping heart monitors to the birds' backs, they rereleased them. Then they gave the birds a series of three tests designed to stress them out. The tests were done in random order over the course of two days, while the heart monitors recorded how high the birds' heart rates rose and how quickly they returned to normal.

One test involved simply walking up to a penguin. A researcher approached the target penguin from a distance while the bird watched, then stopped 10 meters away and stood still for a minute before retreating. This was meant to mimic a tourist taking pictures, or a scientist recording an observation. In a second test, a researcher snuck up behind the penguin while it wasn't watching and banged two metal bars together loudly. This test, which would exercise most humans' hearts too, was meant to represent the loud noises a bird might hear while cranes and trucks move supplies into the research station.

The final test was a capture: what happens to a penguin if researchers need to physically examine it, say, or attach a band to its flipper. Each bird was immobilized for three minutes with a hood over its head before being let go.

Looking at the results from their heart rate monitors, the researchers saw that birds from the busier side of the island weren't as bothered by the stressors they experienced often. A human walking up close, or a loud mechanical noise, didn't bother these birds nearly as much as it bothered the birds from the quieter side of the island.

This might have been because the penguins were simply used to being harassed by humans. Alternately, over the decades of human activities in the neighborhood, all the most stress-sensitive penguins might have fled to a quieter area. "In the field, we notice that some birds are more sensitive to disturbance than others," Viblanc says.

The results of the capture test suggested the first explanation was right. During their brief kidnappings, the penguins from the frequently disturbed group were just as stressed out as penguins from the quiet population. The researchers think this is because captures don't happen very often, so being captured was probably a new experience for all the penguins in the study. Loud noises and visits from humans, on the other hand, are frequent happenings for the penguins living close to the camp. These everyday stressors have become no big deal.

If human activities had driven all but the most relaxed penguins away from the site, then these remaining unflappable penguins should have been calmer than their peers during a capture. Since this wasn't the case, it seems that "the lower stress responses are not a generalized phenomenon," Viblanc says.

Why does it matter? If humans drive animals with certain traits out of a population, we're performing our own (unnatural) selection. It's the difference between teaching your dog a trick and breeding a whole new kind of dog.

Penguins that have mastered the trick of ignoring harmless humans make scientists' work easier, and keep themselves less stressed out. But if humans cause selection for more relaxed animals—here or at sites with other wild animal populations—we might be creating problems for those animals. For example, could calmer penguins be too calm when facing a predator or other threat? "It is hard to say...what the consequences may be in terms of vulnerability to predators," Viblanc says.

There's another reason researchers like Viblanc are keeping a close eye on how well-meaning scientists and tourists affect animal populations. If we force individuals with certain traits away, the whole population becomes less genetically diverse. This gives them less flexibility for adapting to new challenges in their environment. And when a real cause for worry comes along—say, climate change—we want to be sure we've left the little guys with a fighting chance.


Viblanc VA, Smith AD, Gineste B, & Groscolas R (2012). Coping with continuous human disturbance in the wild: insights from penguin heart rate response to various stressors. BMC ecology, 12 (1) PMID: 22784366


Image: A king penguin, by Liam Quinn/Flickr

Climate-Studying Seals Bring Back Happy News

The elephant seals that sent data back from underneath Antarctic ice hadn't exactly volunteered for the task—the sensors were glued to their heads. But it was for a good cause. By taking advantage of animals much better equipped to study frigid polar waters than we humans are, climate scientists collected valuable observations. They even got a rare piece of good news: Some ice shelves aren't melting as fast as we thought.

During the Antarctic winter, "harsh climate, strong sea ice cover and permanent darkness put serious limitations" on the ocean sampling researchers can do, says Tore Hattermann of the Norwegian Polar Institute. That's why researchers from around the world are participating in a program called Marine Mammals Exploring the Oceans Pole to Pole (MEOP). Attaching instruments to various kinds of deep-diving seals lets scientists gather ocean data from places that are more hospitable to animals with blubber.

Hattermann and his colleagues used data from the MEOP's elephant seal brigade to enhance their study of melting under an Antarctic ice shelf. About half of the continent's coastline carries ice shelves, floating glaciers that jut out over the shallow part of the ocean. Warm water from the deeper ocean that gets pushed up under these shelves "has an enormous potential to melt the glacial ice," Hattermann says. (To be clear, what polar researchers call "warm" water is just one degree Celsius above freezing.) The melting of this ice can lead to melting of ice on the Antarctic continent itself—which would add to the rising sea level.

So scientists are eager to know just how much ice these shelves are losing. Since they can't very well put a hundred-mile-long block of ice on a scale, they rely on models that predict the movement of warmer and colder water currents underneath the shelves.

The Norwegian team drilled three holes into the Fimbul Ice Shelf, one of the largest ice shelves on Antarctica. It took an average of 230 meters of drilling to break through the shelf; then they sent instruments another several hundred meters down into the ocean below.

To two years' worth of data from these underwater sensors, the researchers added information collected by nine MEOP elephant seals that happened to have spent some quality time around the Fimbul Ice Shelf. For nine months, these animals swam and dove through the waters the team was interested in, while the sensors stuck to their heads recorded their depth as well as the temperature and conductivity of the water. "The seals just loved it there and stayed around for the entire winter," Hattermann says. This gave the researchers a seal's-eye view of how cold and warm water currents moved during different seasons.

What they saw was less warm water traveling under the ice shelf than previous models had predicted. That means less melting. Based on the cold water they saw underneath it most of the time, the ice sheet may not even be losing mass at all.

Hattermann says it's no surprise to oceanographers that their models need honing. The factors they have to account for are incredibly complicated; in this case, for example, there are small waves and eddies that travel within larger currents and are affected differently by the earth's rotation depending on their latitude. Now that they've collected real observations from the underside of an Antarctic ice shelf, researchers can update their models with a little more optimism.

Just because the news from Fimbul was good, though, doesn't mean it's good all around. Senior author Lars Smedsrud of the Bjerknes Centre for Climate Research says that Fimbul is a typical ice shelf for East Antarctica, so the findings there may apply to similar ice shelves. But he cautions that West Antarctica is a different story. (If you're wondering how to find "east" and "west" on a continent where every direction is north, the two sides are divided by a long mountain range and roughly line up with the Eastern and Western Hemispheres.)

"In West Antarctica there is rapid ice loss ongoing," Smedsrud says. "Hard evidence on why this occurs is still not clear," though the melting of ice shelves there seems to be linked to changing wind patterns. It will take more sophisticated models to keep up with how the warming climate is changing the oceans and the poles. While we're building those models, at least we'll have ongoing help from some flippered assistants.

Tore Hattermann, Ole Anders Nøst, Jonathan M. Lilly, & Lars H. Smedsrud (2012). Two years of oceanic observations below the Fimbul Ice Shelf, Antarctica. Geophysical Research Letters, 39 DOI: 10.1029/2012GL051012

Images by Martin Biuw

Why We (Accidentally) Name Babies for Hurricanes

In the year after Hurricane Katrina made a toilet bowl out of New Orleans, baby names starting with "K" went up by nine percent. Why would new parents want to commemorate the costliest natural disaster in American history? It wasn't their fault, researchers say: The sounds we hear most often stick with us, and we end up bestowing them on our children.

Jonah Berger, a professor of marketing at the University of Pennsylvania's Wharton School, led a study of baby name popularity that will be published in the journal Psychological Science. The researchers looked at the frequency of all first names between 1882 and 2006, a dataset that included more than seven thousand names and 280 million babies.

Each of those seven thousand names was broken into sound chunks called phonemes. For example, "Karen" became five phonemes: K, eh, r, ah, and n. The researchers then asked whether a name's popularity in any given year could be predicted by the popularity of its component phonemes in the previous year. In a year with a glut of Karens, were there extra K's, eh's, r's, and so on popping up in non-Karen names the year before?

Berger and his team found that names were more popular when the phonemes inside them had been more popular the year before. (They didn't count the name itself; Karens from 1999, for example, were removed from the analysis of Karens in 2000.) And the first phoneme—the sound that starts each name—had the most powerful effect. When considered individually, phonemes from the middle or end of a name weren't nearly as influential.

The sounds of the names people hear often, then, seem to sway them when naming their own children. But there are giant tangles of cultural factors determining what names and sounds people have recently heard. To look for a cleaner example of the phoneme effect, the researchers turned to hurricane names.

Hurricanes are named using a rotating alphabetical list that was created in the 1950s. (The list runs A through W, excluding Q and U, which is why you'll sadly never see a Hurricane Xerxes or Quentin. Names that land on especially destructive hurricanes are retired from the list afterward, like MVP jersey numbers.)

The researchers guessed that after a very bad hurricane, when people were inundated with news reports mentioning Andrew or Bob or Irene, there would be an increase in babies with similar names. And since hurricane names are predetermined, the effect would be separate from any already-existing cultural influences (princesses, actors, tennis players).

After collecting data on every hurricane between 1950 and 2009, Berger and his colleagues looked at how baby names that shared phonemes with a hurricane changed in the following year. They found that damaging hurricanes were followed by a clear uptick in similar names.

Names are more likely to be trendy, Berger writes, when names with similar sounds have recently been popular. The effect might not be limited to names; other research has hinted that we favorite-playing humans prefer towns and occupations that share our initials. It seems we just can't help growing fond of familiar sounds.

If you want to see how popular your own name has been over the decades, what this year's top ten boy and girl names are, or how name popularity varies by state, you can do so at the Social Security Administration's baby names site. You'll also find all of Irene and Andrew's relatives at the Weather Underground hurricane archive. You may discover that your parents were just following the trends—or the tropical storms.



Jonah Berger, Eric Bradlow, Alex Braunstein, & Yao Zhang (2012). From Karen to Katie: Using Baby Names to Understand Cultural Evolution Psychological Science


Image: Tommy Lew/Flickr

Space Census Finds Extra Penguins, Poop

Playing what might have been the world's most tedious game of Where's Waldo?, scientists used photos taken from space to count all the emperor penguins in Antarctica. They found more than a hundred thousand birds that hadn't been spotted before. The news may affect the penguins' fate in a warming world. Besides, what's a better surprise than extra penguins?

Researchers from several institutions, including the British Antarctic Survey in Cambridge, undertook the emperor penguin space census. They thought previous penguin counts might not be accurate. For one thing, the last estimate of the Antarctic penguin population is almost 20 years old. For another, humans can't easily travel very far from their Antarctic research bases to seek out half-frozen bird huddles. So penguin colonies that are farther out in no man's land might have never been spotted by people.

Thanks to emperor penguins' habit of clumping together in giant colonies during breeding season--and their convenient lack of camouflage against the snow--the researchers knew high-resolution satellite photos should reveal the penguins. They used images from all around Antarctica's coastline, where penguin colonies camp out. Forty-six colonies appeared, including several that hadn't been counted before.

A penguin colony on the Antarctic coastline, spotted from above.

After zooming in on each colony and sharpening the images, the researchers used computers to count the penguins one by one. The challenge was for the computer to decide which dark pixels represent penguins, rather than shadows on the snow--or penguin poop. Author Peter Fretwell explains that in this method, "you 'train' the computer to recognize the pixels that are penguin, guano, snow or shadow by giving it sample pixels. The computer then goes away and splits the whole image into each pixel type."

Zooming in on a penguin colony and sharpening the image. I think I found the guano.

As long as the images have a high enough quality, Fretwell says, this technique is "usually quite accurate." Where the satellite pictures were more shadowy, penguin counts would be a little less certain. For some of the colonies, though, researchers were able to check their numbers against estimates others had made from the ground or from aerial photography.

And then there were the missing penguins. All the satellite images were taken during the breeding season, when emperor penguins congregate to create adorable new baby penguins. The new parents take turns babysitting: While one penguin takes care of the chick, the other goes out to sea and swallows lots of fish to regurgitate later. While the chicks are small, they spend most of their time balancing on top of their parents' feet to keep warm. Once the chicks are old enough to walk around on their own, both parents may leave to forage.

So for every individual counted in a satellite photo, the authors assumed there was a hidden chick and a second adult at sea hunting for food. (They were only interested in counting breeding adults, not the chicks, most of which will die.) Later in the season, some of the penguin pixels may have been kids instead of adults. But since a young penguin standing on the ice probably has two parents away foraging, the researchers figured that pixel still stood for two adult penguins.

The final count was about 595,000 adult emperor penguins in all of Antarctica. That's roughly the (human) population of Milwaukee. It's also substantially higher than the last estimate, which put the population between 270,000 and 350,000 adult birds.

The census could easily have overestimated or underestimated the true number of penguins. But, Peter Fretwell says, "The main thing is that this gives us an initial benchmark from which we can monitor emperor penguin numbers in the long term."

As climate change tightens its grip on every part of the globe--all the way to the poles--penguins will certainly see some changes around them. The sea ice along the coastlines they inhabit will disappear; shifting food webs may make their prey scarcer; and severe storms might become more frequent. Knowing how many emperor penguins are there now, and where to find their colonies, will help scientists monitor how the species is coping with the changes. We might even be able to keep them from becoming harder to find than Waldo.

Fretwell, P., LaRue, M., Morin, P., Kooyman, G., Wienecke, B., Ratcliffe, N., Fox, A., Fleming, A., Porter, C., & Trathan, P. (2012). An Emperor Penguin Population Estimate: The First Global, Synoptic Survey of a Species from Space PLoS ONE, 7 (4) DOI: 10.1371/journal.pone.0033751 


Image: Close-up penguins from Hannes Grobe/AWI/Wikimedia Commons; satellite images from Fretwell et al.


Note for British readers: You may know Waldo as Wally.

Dinosaur Age Not Dramatic Enough? Add Fire

As if a world dominated by hungry, house-sized lizards weren't sufficiently exciting, scientists have added another set piece to our image of the Cretaceous: raging wildfires.

The Cretaceous period, which ended about 65 million years ago with the extinction of the dinosaurs, was hot. That's thanks to volcanos that pumped carbon dioxide into the atmosphere and created a greenhouse effect. Researchers from London and Chicago now say it was also a "high-fire" world. Frequent blazes may have kept animals on the run, created some of the fossil beds we study today, and helped determine which plant species survived into the next era.

Led by graduate student Sarah Brown from the Royal Holloway University of London, the researchers tracked the appearance of charcoal in ancient sediments. Like a set of sooty footprints right through the fossil record, the charcoal evidence showed when and where fires had occurred.

The team saw that wildfires had increased during the Cretaceous period. These fires were probably sparked by lightning, and their flames were fanned by the high concentration of oxygen in the ancient atmosphere. Today, oxygen makes up about 21% of our air. But during the Cretaceous, it may have risen as high as 25% or more.

This high oxygen content, the authors say, would have allowed plants to burn without being bone dry. A spark in a green forest, instead of dying out as it would today, might become a full-blown fire.

Brown and her coauthors did not find any evidence that these fires contributed to killing off the dinosaurs. But they note that after a fire burns through a piece land, erosion is likely. There may be rapid flooding or mudslides. In the Cretaceous, these events might have trapped and killed dinosaurs and other animal life--and helped preserve their bones.

The authors point to certain fossil beds that lie in floodplains and contain charcoal, as well as plant and animal remains. These could be sites where wildfires triggered flooding, conveniently sweeping lots of informative fossils into one place for future scientists to find.

Charred plant remains in these fossil beds provide another clue about the effect of fire. As the Cretaceous went on, the types of plants being fossilized gradually changed. Flowering plants, called angiosperms, became more and more common. Gymnosperms--the more ancient, flowerless species such as cone-bearing trees, cycads, and ginkgos--faded into the background.

A charred flower fossil from the Late Cretaceous.

Frequent fires may have given an added edge to the angiosperms. The new types of plumbing these plants had invented let them grow faster and more efficiently. Rather than trees, the flowering plants growing during the Cretaceous seem to have been weedy and shrubby types. After a fire, they could regrow faster than the gymnosperms. And their new growth provided fresh fuel for wildfires, creating a cycle that encouraged the growth of flowering plants and left older models in the dust.

Though fire didn't do in the dinosaurs, then, it may have helped set the stage for the dominant plants of the modern age. (As if we needed any more drama.)

Brown, S., Scott, A., Glasspool, I., & Collinson, M. (2012). Cretaceous wildfires and their impact on the Earth system Cretaceous Research DOI: 10.1016/j.cretres.2012.02.008


Images: Gorgosaurus from Nobu Tamura/Wikimedia Commons; flower fossil from Brown et al.

Seeds from 30,000-Year-Old Squirrel Cache Flower Again

Confession: As a nerdlet of nine or ten, I decided to help flowers get fertilized. I loved seeing the glossy seeds hidden inside the fat green ovaries of dead flowers when I split them open with my thumbnail. I must have watched one of those nature specials where the scientists climb up to the top of the Alps and dust pollen onto endangered flowers with a paintbrush, because I started going around roadside fields with cotton balls and gathering pollen. Partway through my project I realized that these particular plants were doing fine without human intervention, and abandoned them.

Now, a group of Russian scientists has given some help to plants that were, unlike my backyard buttercups, definitely not going anywhere on their own. The seeds and fruits of Silene stenophylla were buried 12 stories deep in the Siberian permafrost. They'd been cached there by a ground squirrel some 30,000 years ago. After digging up these long-frozen specimens, a team led by Svetlana Yashina managed to resurrect the ancient organism. They grew healthy plants that flowered and produced their own new, fertile seeds.

When the team excavated this ground squirrel's hoard, they could tell from the ice structures around it that the spot hadn't been touched--or thawed--since it was first interred 30 millennia ago. Though the industrious squirrel had stored a variety of seeds and fruits, previous studies had shown that the seeds of S. stenophylla had a little more liveliness left in them than the others.

From unripe fruits of S. stenophylla, the researchers extracted placental tissue. (Yes, flowering plants have placentas; it's the place where each seed attaches to the ovary. This was news to me too.) They grew this tissue on its own, coaxing it to develop into actual plant shoots. These shoots were fed and grown up into real, potted, flowering plants.

Alongside the ancient and reconstituted plants, the researchers also grew modern plants of the same species. The ancient plants produced up to twice as many flower buds, as if excited to be alive again.

Once the plants had become flowering adults, there were notable differences between the ancient and modern versions. The ancient plants' flower petals, for instance, had a narrower and more shallowly bisected shape. (You can see one of the modern flowers below, and an ancient flower at the top of this page.) The plant was like a snapshot from an earlier stage of its evolution.

Not only did the plants grow and flower--thirty-six of them!--but they were fertile. Scientists demonstrated this by artificially pollinating the plants with each other's pollen (like me with my cotton balls, sort of). Eight or nine weeks later, the plants produced seeds. When scientists gathered these seeds for germination, 100% of them successfully sprouted into new plants. As adults, they grew the same unusual, ancient flower petals that their parents had.

No one has brought a plant this ancient back to life before. The oldest viable seeds ever found are from the first century BC. Yashina writes that the rapid, deep, and permanent freezing of this squirrel's pantry effectively preserved the plant tissues inside. A similar strategy is employed today at the Svalbard Global Seed Vault in Norway, where samples of seeds from around the world are held in an under-ice bunker. If the world's other seed banks are someday destroyed or abandoned, the Svalbard stock can be used to reestablish our crops.

As for seeds that have been unintentionally frozen, there are countless more under the world's icy regions. Permafrost covers a fifth of the planet's surface. If scientists can find other viable plant tissues preserved beneath it, they may discover more species that, like S. stenophylla, have changed since they were frozen--or they could reanimate plants that are now completely extinct.

There's another potential reanimation to consider. Under the permafrost is a rich community of microorganisms, frozen and preserved like the fruits of S. stenophylla. But unlike the flowering plant, which required plenty of manipulation to bring back to life, these organisms are built to last. David Gilichinsky, the senior scientist on this study, has resurrected permafrost bacteria that were frozen for millions of years.

"They are very tough little guys, especially if they are capable of forming spores," McGill microbiologist Lyle Whyte told me. Whyte was not involved in the plant regeneration study, but researches microbes in the Arctic permafrost. He adds that bacteria in, say, million-year-old permafrost may not be quite that old themselves--there's evidence that these frozen communities actually grow and reproduce very slowly while trapped under the ice.

As climate change begins to thaw the permafrost, will some of these frozen microorganisms be awoken and released into the above-ground world? Whether they've been in suspended animation for thousands of years, or quietly reproducing for millions, these microbes would represent strains that modern-day species have never been exposed to. Ancient bacteria--or perhaps viruses or fungi--might discover that the modern world is fertile ground. Humans might discover the Neanderthal flu.

Sadly, David Gilichinsky himself passed away just two days before the publication of his remarkable plant regeneration discovery. "David was at the same time a great expert [on] microorganisms isolated from the cold permafrost and a warm-hearted friend," a colleague wrote on a memorial page. Although Gilichinsky will be greatly missed by his scientific community, he leaves behind him the message that even something unthinkably long gone can be brought back to flowering life.


Svetlana Yashina, Stanislav Gubin, Stanislav Maksimovich, Alexandra Yashina, Edith Gakhova, & David Gilichinsky (2012). Regeneration of whole fertile plants from 30,000-y-old fruit tissue buried in Siberian permafrost. PNAS : 10.1073/pnas.1118386109


Photos: Yashina et al.

When We Talk about Snow

"Excuse me," the man next to me on the train said mildly, turning in his seat. "Do you remember what you did in the snow?"

"Sorry?"

"They say it was exactly this day last year that we had all that snow," he said. "So I was wondering, what did you do? Were you working? Did you go home early?" The man was middle-aged, with pale eyes that weren't quite right. He clutched a dirty bag in his lap with both hands.

"Um. They sent us home early, yeah."

"I wish I had a better memory," he said, smiling regretfully.

"You don't remember what you did?"

"About nine o'clock at night," he said, "I remember, I went to go check out the snow. I walked a block or two down the street, but then I saw all those big, huge snow drifts. And I thought, well...if something happened, there was no one around to pull me out, you know?"

Chicagoans called that February 2011 storm the Snowpocalypse. The snow came down furiously all evening. Muffled cracks of thunder sounded from high inside the blizzard. On the highway that runs the city's length, the whiteout slowed traffic to a stop, then froze it in place. Commuters were stranded overnight and had to be rescued by firefighters.

"I wonder," the man on the red line continued, "if you could ask everyone what their ideal snow is, what they would say. Like maybe somebody says, I'd like half an inch of snow between nine and nine-thirty, and that's it!"

"I like a lot of snow," I offered. "But I don't have a car."

"I like a lot of snow, too," he said. We both looked out the window at the gray cityscape, snowless in a 40-degree February.

Chicago isn't the only place experiencing a weirdly temperate winter. Most of the United States has had a warm and dry couple of months. Meteorologist Jeff Masters says that an extremely out-of-the-ordinary jet stream is to blame. Warm air from the Southwest is being pushed across the rest of the Lower 48.

That's funny; I remember when forecasters were telling us this winter would be "another brutal one." But weather is chaotic and hard to predict. That's why climate change models can't tell us for sure whether this freakish year is our fault. Would this one warm streak have happened without our influence, or is it part of the larger pattern of global warming?

Our fault or not, it's hard to talk about this year's unwinter without thinking of climate change. It's not impossible, though. The L.A. Times ran a whole article about the warm weather ("If you looked at U.S. temperatures, you'd say, 'Wow, it was a warm winter,'" says a quoted expert) without once mentioning the climate.

The Wall Street Journal, rather than similarly ignoring climate change in the face of a balmy winter, published an opinion piece called "No Need to Panic about Global Warming." The letter was signed by "sixteen concerned scientists," including at least one (named Claude Allegre) who is also not panicked about asbestos causing cancer.

Previously, the Wall Street Journal had rejected a similar but opposite piece, on why we do need to be concerned about climate change, signed by 255 scientists. Science magazine published that letter, which you can read here. And the Wall Street Journal itself published a rebuttal to the original op-ed. (I won't rehash any of those arguments here, but you can check out my toolkit for talking to climate change deniers.) Unfortunately, when misinformation oozes into the mainstream, it's notoriously sticky to clean up. Rebuttals and corrections can't erase what people have already seen and believed.

You might notice that several signatories of the original Wall Street Journal piece are meteorologists. This is a group especially resistant to the idea of climate change: a 2010 study found that fewer than a third of TV weathercasters believe humans are causing global warming. It may be a problem of seeing the forest through the snow-covered trees. When broadcasters are doing their reporting from the middle of a blizzard, it must be hard to imagine that the world is getting hotter.

I chatted with a man in the Raleigh-Durham airport who looked to be around retirement age. He was an engineer traveling to Chicago for an enormous meeting of people in the heating and cooling businesses. I told him I edit a children's science magazine.

"So you write about the environment? Climate and stuff?" he asked.

"Sure we do," I said. I asked if global warming was a major topic at a conference like this one.

"Well," he said. "I don't know about that warming."

Then he described to me some of the big issues in his industry, such as benefits companies can receive by meeting certain energy standards. "Reducing the carbon footprint of buildings, that's huge," he said.

"If you're talking about reducing carbon footprints," I pointed out cautiously, "that's because of climate change."

"Oh. Sure, I guess," he said. The connection didn't seem to have occurred to him.

Maybe it's impossible right now to show everyone the big picture, the snowless woods behind those icy branches. In our country, climate change has been made into a political issue, rather than an issue of living on the planet. But if people are willing to accept smaller practicalities--tax credits, efficiency requirements, gas prices, different cars on the road--then it might not matter how they perceive the big picture. If the guy in the airport is lowering people's carbon emissions, it makes no difference to a polar bear that he's also reading the Wall Street Journal.

And once people notice the snow is gone, maybe then we'll be able to talk about it.

Photos: by me.

Which Ancient Megafauna Did We Wipe Out?

If things had turned out differently in past millennia, modern-day animal lovers wouldn't have to fly to Kenya to go on safari. North America was once overrun with tourism-worthy animals: Aside from the iconic woolly mammoth, there were saber-toothed cats, giant sloths, and short-faced bears more than twice as massive as a grizzly. We're still not sure what happened to them, but a new study in Nature attempts to untangle the whodunnit.

Since dozens of these "megafauna" species disappeared from the Americas, Eurasia and Australia just as humans were arriving, it's tempting to blame ourselves. The human love of the mixed grill, after all, runs deep.

But the mass extinction, beginning around 50,000 years ago, coincided with another key event: the end of the last ice age and shift to a warmer climate. So controversy over what killed off the ancient megafauna has persisted.

To tackle the large-scale, globe-spanning question, a large and globe-spanning team of researchers decided to take it species by species. Even though the animals went extinct around the same time, they might have been individually done in by different factors. The researchers looked at ancient animal remains and human remains from around the world, as well as DNA samples from the megafauna. The genetic material told them about each species' diversity over time (species with more genetic diversity are better able to adapt to changing environments), and the overlap of human and animal remains showed when and where we coexisted.

Woolly rhinoceros: Not our fault.

The study focused on just six animals. All of them were herbivores living in North America or Eurasia, and some of them have living members today but inhabit a greatly reduced range. 

The woolly rhinoceros, pictured above, used to live in Eurasia but is now extinct. The researchers found that the woolly rhino's population size was actually increasing well after the species came in contact with humans, and there's no evidence that we commonly preyed on (or even came in contact with) the rhino. This would seem to vindicate us--it was probably the warming climate, not humans, that wiped out the woolly rhinoceros.

Wild horse: Our fault.

The wild horse or tarpan, Equus ferus, is also extinct today (and not to be confused with wild populations of domestic horses). The species maintained a large Eurasian population well into the warming period, suggesting that climate change wasn't what ultimately killed it. The overlap between wild horse and human populations, as well as the abundance of wild horse remains at human archeological sites, hints that we may have hunted the species to death.

Woolly mammoth: ?

As for the poor mammoth, the data are disappointingly unclear. Our ranges overlapped in both Eurasia and North America, and ancient North Americans are known to have hunted the mammoth. But the mammoth's population in Eurasia, like the woolly rhino's, was still increasing after it came in contact with humans, and its range may have begun to shrink as the weather warmed. It could have been either culprit that ultimately killed the mammoth, or a fatal combination of human hunting and climate change together.

That fatal combination is what makes this sort of research--the cold cases of paleontology, if you will--urgent today. We're again experiencing warming, though it's happening much, much faster than in the age of the mammoths. Simultaneously, we're pushing species out of their habitats or poaching them into extinction. The authors of the new study didn't find any one feature, such as a genetic signature or a distinct pattern of distribution, that predicted which animals lived and which died. That means we're no closer to guessing which of today's species will survive climate change and human involvement--like the reindeer, which lived through the extinction of its fellow megafauna and thrives today--and which will go the way of the mammoth.

Images: PLoS/Mauricio Anton


Lorenzen, E., Nogués-Bravo, D., Orlando, L., Weinstock, J., Binladen, J., Marske, K., Ugan, A., Borregaard, M., Gilbert, M., Nielsen, R., Ho, S., Goebel, T., Graf, K., Byers, D., Stenderup, J., Rasmussen, M., Campos, P., Leonard, J., Koepfli, K., Froese, D., Zazula, G., Stafford, T., Aaris-Sørensen, K., Batra, P., Haywood, A., Singarayer, J., Valdes, P., Boeskorov, G., Burns, J., Davydov, S., Haile, J., Jenkins, D., Kosintsev, P., Kuznetsova, T., Lai, X., Martin, L., McDonald, H., Mol, D., Meldgaard, M., Munch, K., Stephan, E., Sablin, M., Sommer, R., Sipko, T., Scott, E., Suchard, M., Tikhonov, A., Willerslev, R., Wayne, R., Cooper, A., Hofreiter, M., Sher, A., Shapiro, B., Rahbek, C., & Willerslev, E. (2011). Species-specific responses of Late Quaternary megafauna to climate and humans Nature DOI: 10.1038/nature10574