Wild Things
Slate’s animal blog.

Oct. 2 2015 2:00 PM

There Aren’t Enough Male Squirrels to Mate With All the Females

Do you ever look in the mirror and think there’s something wrong with you? That maybe your tail isn’t bushy enough, your pelt’s lost its luster, or you’ve eaten a few too many acorns lately? Well, cut it out! I’m here to tell you that it isn’t you—it’s them. No, it’s not your imagination, single women: There literally aren't enough men out there!

That last sentence is the actual headline of a Vice article that presumably exists to make single women feel better about themselves and their supposed predicament. But it’s also scientifically true—at least if you’re a yellow ground squirrel. In the past, zoologists had thought that female squirrels’ lack of romantic encounters stemmed from their body condition, age, or competition from other female squirrels. Now, we know that the main reason some females aren’t having babies is that there aren’t enough males around—and the ones that are around are having a hard time finding them.

A shortage of males has been shown to be a factor in female reproductive failure in some insects, fish, and spiders. But in most mammals, it’s the reverse: Females tend to be the limiting factor. After all, one male can impregnate plenty of females. Plus, raising the young takes time and resources—just ask your mom!—and most of that burden falls to the females. Sadly, male squirrels aren’t really into parenting: “They mate, and they eat,” as zoologist and study author Nina Vasilieva puts it.

"When you touch them they seem nearly liquid," says study author Nina Vasilieva of Russian male yellow ground squirrels, which are larger than their American counterparts.

Olga Batova

But when Vasilieva studied the sex lives of wild squirrels near the Russian village of Dyakovka over four years, she found some unusual traits that made females the scarcer resource. First, female yellow ground squirrels live alone in single-squirrel burrows, where they spend nine months out of the year quietly sleeping. Second, when they finally do emerge, they have a very limited span of time—as short as a single day—in which they are receptive to mating. If they fail to mate within that time, they have to wait until the following year. And, given that their lives last a brief two to three years, that's cutting it close. "I actually saw with my own eyes some sad females which were not visited by any males," Vasilieva says forlornly. 

Before you feel too sorry for the females, though, consider that it's no walk in the park to be a male squirrel either. After all, he's stuck chasing an elusive, silent target that pops up once a year. Where’s squirrel Tinder when you need it?

Make no mistake: These females want to mate. In squirrels, “it’s reasonable for females to invest in reproduction as much as possible, even if she is in bad physical condition,” says Vasilieva. “Female ground squirrels have a very low reproductive cost. Actually, reproduction does not affect female survival and future reproduction in yellow ground squirrels at all.” But they aren’t exactly making it easy for the male squirrels. As a result, researchers found that 30 to 40 percent of sexually mature females failed to reproduce, they reported Friday in the journal Science Advances.

This finding goes well beyond squirrels: The dearth of males at the right time and place could also apply to lemurs or to other hibernating rodents, Vasilieva says. But perhaps there’s a larger message here for us all. Ladies, stop blaming yourself for the fact that there don't seem to be enough eligible men around. You’re perfect just the way you are. But also, best not to spend the majority of your time in an underground hole.

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Sept. 25 2015 2:53 PM

Watch a Majestic Siberian Tiger Get Released Back Into the Wild

It’s Friday. Fall (and football) is here. Weather’s supposed to be decent. All that being the case, at about 4 p.m. this afternoon, you’ll likely be pacing around your office like a tiger in a cage, ready to be released into the wild of the weekend. And for an idea of what that will look like, watch the video above.

The video in question—which comes to us from the good people at GoPro—shows Zolushka, a Siberian tiger, being returned to the wild. Rescued from poachers by the International Fund for Animal Welfare as a cub, her re-entry is just one example of the organization’s larger attempts at restoring the global tiger population. While there were once more than 100,000 wild tigers in Asia, that number is now believed to be somewhere between 3,700 and 4,200.

So not only is the incredible footage a thrill to see, it also affords us the opportunity to watch good, meaningful work in action—and, of course, provides a little Friday afternoon inspiration as well.

But be warned: Should you try to mimic Zolushka’s sprint for freedom after clocking out today, be prepared to be significantly less majestic in doing so. 

Sept. 24 2015 4:49 PM

Ridiculously Gorgeous Rare Bird Finally Photographed

It's hard to believe the mustached kingfisher is a real bird. First of all, it looks more like a Baltimore Orioles–themed stuffed toy than a bird. Second, it's only found on the remotest of mist-caressed islands, similar to the legendary Pokemon bird Articuno. Finally, it has long eluded human capture, with only three specimens ever before collected, all females. “Beautiful but very cryptic,” is how birdlife.org describes it. “Very few sightings, and male plumage remains undescribed.”

Until now.

Last week, a team led by Chris Filardi, director of Pacific Programs at the American Museum of Natural History’s Center for Biodiversity and Conservation, identified and photographed the first-ever male mustached kingfisher. It happened one fateful morning while the team was surveying biodiversity in the mountainous forests of the "sky island" of Guadalcanal in the Solomon Islands.* Suddenly, Filardi heard the unmistakable call: “ko-ko-ko-kokokokokokokoko-kiew!” A dark shape criss-crossed his path. And then, silhouetted against the dappled sunlight, he saw it: the mustached kingfisher in its full, mustachioed glory.

A kingfisher bird.
A kingfisher bird.

Photo courtesy American Museum of Natural History/Sammy Qalokale

He put down his binoculars. He didn't need them anymore.

"It was like finding a unicorn," he told me over the phone. "It’s unimaginable. You dream about it. You can almost taste it. And all of a sudden, there it is.”  

This was “a bird I have sought for nearly 20 years,” he said in a beautifully written blog post. “One of the most poorly known birds in the world was there, in front of me, like a creature of myth come to life.” 

Thanks to Filardi and his team, we can now describe the male’s plumage: His head is a burnt orange, his beak is a split-open carrot, and his “mustache” takes the form of two violet bands, one around his chin and the other extending from his eyes, lending him both decoration and dignity. He juts forth the pale roundness of his fluffy breast, indignant. 

Firaldi holding a puppet, I mean mustached kingfisher.
Filardi holding a puppet—I mean, mustached kingfisher.

Photo courtesy American Museum of Natural History/Rob Moyle

The remote "sky island" of Guadalcanal, Papua New Guinea.
The remote "sky island" of Guadalcanal.

Photo courtesy American Museum of Natural History/Patrick Pikacha

The Uluna-Sutahuri people of Guadalcanal have long lived in the midst of this legendary bird, which is known to them as Mbarikuku. But this is the first time it has been photographed and recorded. Due to habitat degradation (logging) and deadly predators (pesky invasive cats), the kingfisher is exceedingly rare, with numbers estimated at between 250 and 1,000 and dwindling. 

Previously, taxonomists had lumped together this bird and a very similar one, the larger Bougainville mustached kingfisher. The new observations made by Filardi's team reveal that this is almost certainly its own species, based on its distinctive call, reproductive isolation and history, and “striking difference in plumage." The next step is to run genetic tests on the captured specimen, to see how different the two species truly are.

As Filardi puts it: “The question is: Is it a Siberian tiger and a Bengal tiger, or is it a Bengal tiger and a lion?”

*Correction, Sept. 24, 2015: This post originally misstated that Guadalcanal is in Papua New Guinea. It is in the Solomon Islands.

Sept. 4 2015 2:21 PM

Between a Hawk and a Hard Place

Finding the perfect place to raise your precious little ‘uns is no easy feat. It's a lot harder if you happen to be a hummingbird. Now, instead of school districts and playgrounds, you’ve got to worry about pesky jays snatching your young straight from the nest. Fortunately, nature has the solution: Just add hawks!

That’s what researchers from the University of Arizona found out after following the fates of more than 300 black-chinned hummingbird nests in the Chiricahua Mountains over three years. These hummers, along with Cooper’s hawks and Mexican jays, coexisted in what ecologists call a “trophic cascade,” a food web in which the behavior of top-level predators directly impacts the survival of those below it. They published their findings today in the journal Science Advances.

Researchers knew that hummingbirds tended to cluster their nests close to hawks. But at first, they couldn’t figure out why. It turned out that, while hawks didn’t pose much of a danger to tiny, agile hummingbirds—“They’d burn more calories chasing them than they would get from catching them,” says Harold Greeney, who led the study—they sure made the jays nervous. So whenever there were hawks roosting nearby, the jays set up shop in the trees far above them, out of the way of hummer territory.

When the researchers plotted the success of hummingbird nests and compared it to the vicinity of hawks, they found a “cone of protection”: an oasis in which hummingbirds could raise their families in peace, enjoying a better chance of survival. Hawks, it turned out, were hummingbirds’ winged protectors.

A stroke of luck aided researchers in discovering the profound impact that these taloned angels had on hummingbirds’s livelihoods. The summer after their first year of observations, a host of raccoonlike mammals called coati climbed up into the trees in the research site and ate as many hawk nests as they could lay their claws on. Within two weeks, researchers saw the cone of protection effect disappear—revealing how much the hummers relied on hawks for their protection. “It was so fortuitous,” Greeney says, adding, “Well, for us. Not for the hawks.”

Once the hawks were gone, the jays moved in, targeting both eggs and hummingbird babies. “Every single hummingbird got eaten,” says Greeney, whose extensive hummingbird expertise has been featured in PBS documentaries.

These new findings provide conservationists with a clear example of how ecosystems can be interconnected on a deep level. The hummingbird-hawk system is not unique: A similar system exists in the Arctic, where snow geese prosper when they cluster around snowy owls who viciously attack their enemy, the arctic fox. In freshwater lakes, algae blooms best in places where predatory crayfish keep away smaller fish and snails that feed on algae.

When humans mess with these kinds of systems, or even try to preserve them by protecting one species, they risk disrupting a delicate balance in which each animal species affects the others. As Greeney puts it: “For conservation, no animal is an island unto itself.” 

Sept. 3 2015 2:20 PM

The Dog (and Meerkat and Polar Bear) Days of Summer

Sept. 2 2015 4:19 PM

What Makes an Animal “Cute,” Anyway?

Scientists on social media are redefining “cute.” Prompted by two researchers at Virginia Tech, Anne Hillborn and Marcella Kelly, scientists have been posting photos of their most adorable research organisms to Twitter with the hashtag #CuteOff. Whether or not these critters qualify may be in the eye—or the research study—of the beholder.

It’s hard to argue against the appeal of some of these cute and cuddlies, like a cheetah cub:

Though sleeping monkeys will give that cub a run for its money.

Then again, who doesn’t love a teeny tiny frog?

But you might find it a bit harder to find these specimens particularly adorable.

You may have mixed feelings about sea pigs, but come on, it’s called a sea pig.

Someone described this tenrec as a “cute little monster.” Maybe cute, but certainly not cuddly.

The Field Museum wants you to appreciate the squeee-worthiness of this bat. No? Come on, just a little squeee. Look at it!

What we’re learning from #CuteOff is that one person’s “squeee!” may be another person’s “squ ... ewww.”

So what’s going on here? Do researchers really think their own study organisms are the cutest in the land, or are they biased? What makes a creature cute?

It could be big eyes. Asked about this by a reporter, Kelly responded, “I think that’s probably part of it, especially with baby animals, but there were plenty of animals that did not have big eyes …” (“Or any eyes,” the reporter interjected) “that scientists tweeted that I thought were surprisingly cute.”

Researchers who study humans’ preferences for physical attributes of other species or inanimate objects have found that infant-like features, such as large, wide-set eyes and an enlarged head, as well as human-like traits, are considered most appealing. Since the middle of the 20th century, researchers (and pet product marketers, certainly) have been investigating this phenomenon and its implications.

Recent research by Julie Hecht and Alexandra Horowitz showed that most of the undergraduate students participating in their study who were shown digitally-manipulated photos of adult mixed-breed dogs preferred the photos of dogs with bigger eyes, more space between their eyes, and smaller jowls. Hecht and Horowitz’s findings support those of other researchers who showed that dogs exhibiting paedomorphic, or juvenile, facial expressions are preferentially selected by humans, giving them a competitive advantage in their modern environment. This suggests that the domestication of wolf populations involved not only selection for tameness, but perhaps trended toward irresistible “puppy-dog eyes,” as well. Humanlike personality cues are also important when it comes to our animal friends’ faces. In Hecht and Horowitz’s study, participants were likely to prefer photos of dogs with colored irises and a distinct “smile,” characteristically human-like traits.

The appearance of wide-set eyes and a smile certainly make this nudibranch a contender for the #CuteOff.

In humans, symmetry and averageness are typically perceived as attractive traits. A more average face is one that is more similar to a computer-averaged composite of multiple faces. In 2003, Jamin Halberstadt and Gillian Rhodes tested whether this principle applies to humans’ perceptions of birds, fish, and an inanimate object—an automobile. Using computer-generated line drawings, the researchers found that a sense of familiarity was associated with study participants’ preference for the more average drawings of all three items. Halberstadt and Rhodes also discovered a general preference for “averageness,” independent of a sense of familiarity, for birds and fish; multiple research studies have suggested this is tied to our perception that a more average face is an indication of genetic or physical quality.

These studies may help us understand why wide-eyed furry mammals tend to be easy, go-to entries in the #CuteOff, or why one cheetah is considered cuter than another, but they still don’t really explain why some researchers consider the “ticks of the sea” legit contenders for the #CuteOff and the rest of us, well ...

Perhaps this is related to the fact that we think our dog, cat, rabbit, hamster, fish, snake, or child, is the cutest of all the dogs, cats, rabbits, hamsters, fishes, snakes, or children, for reasons certainly related to our personal bond or connection with them. In the same vein, maybe each researcher is going to think her study critter is the cutest of all the study critters, even if it is prickly, slimy, blood-sucking, creepy-crawly, or just plain devilish.

But, really, I do have the cutest dog of all the dogs.

Does cute matter?

Physical preference can affect decision-making, and when it comes to scientific research, conservation, and pet adoption, it turns out cute does matter. As Hecht and Horowitz point out, the endangered species that tend to get the most attention are those more closely related to humans or with “decidedly human-like” characteristics. Additionally, studies have reported that appearance and personality are two of the key factors affecting people’s choice of pet when adopting from a shelter. Shelter staff and volunteers should help potential adopters find the pet that is the best fit for their family and home to discourage picking an animal based on appearance alone.

Sometimes, cute can be overrated.

Sept. 1 2015 12:13 PM

Animals That Scientists Thought Never, Ever Have Sex Actually Do Have Sex

This article originally appeared in Sick Papes, a blog about exciting new science papers.

As all you puddle-suckers know, there are entire universes of microscopic organisms living in every drop of puddle water, moss moisture, and sidewalk juice. Indeed, it was within a drop of filthy gutter scum that Antony van Leeuwenhoek (1632–1723) observed single-celled and other microscopic organisms for the first time. He also provided the first microscopic drawings of human sperm, which lead to some great drawings of little tiny men scrunched up inside the head of a sperm. [Editor’s note: this man-in-sperm theory is no crazier than the truth of how humans develop.] The revolutionary nature of Leeuwenhoek’s observations are even more impressive considering how shitty the microscope that he used was: Made of a single hemisphere of glass fixed to a metal plate, these scopes had a fixed focal distance of about 0.5 millimeters but magnified up to 275 times, and apparently had a resolution approaching one micron.

Today’s Sick Pape focuses on one of the types of animals that Leeuwenhoek saw when he magnified a drop of water: rotifers. Rotifers are microscopic animals (not bacteria, not amoebas—multicellular animals) measuring between about 100–500 microns yet possessing a complex anatomy including a nervous system and a digestive system. And for the past two decades, rotifers in the genus Bdelloidea have been the subject of intense research for one reason: They never, ever have sex.

Sexual reproduction is thought to be essential for the long-term survival of a species. There are a handful of animals that will occasionally pop out a virgin birth, but this is typically done just for a ratings bump at Animal Planet during the holiday season. In general, there are no species that exclusively reproduce asexually and manage to last more than a few million years. While there may be short-term Darwinian benefits to cloning yourself, only sexual reproduction can provide the cosmic intermingling and chromosomal diversity that organisms need to survive the long evolutionary grind.

Bdelloid rotifers thus pose a major question: How has this species survived for hundreds of millions of years without ever having sex? Male bdelloid rotifers have never been observed, nor has anyone ever witnessed meiosis or mating. Instead, the females just happily clone themselves forever like a goddamn metaphor I can’t think of right now. The big question has always been: How come these ladies haven’t gone extinct? What’s their secret?

Over the past few decades, bdelloid rotifers have been whispering their secrets into the quivering ears of Matt Meselson’s lab. Meselson is one of the best scientists who has ever lived, responsible for “the most beautiful experiment in biology” as well as helping to discover mRNA and many other Old Testament breakthroughs (as well as crusading for years against biological weapons). Which is just to say, he knows what the funk he’s talking about. And his lab has shown that bdelloid rotifers have a variety of alien mechanisms for increasing their genetic diversity without having sex. Namely, these rotifers suck up random DNA from their surroundings and shove it into their own genomes, and they also shatter their entire genome and then rebuild it with errors.

And now, Meselson (who is currently in his 80s) and his lab have done something that is so rarely done these days: They have provided strong evidence that their entire premise was wrong and that bdelloid rotifers actually do reproduce sexually. I want to emphasize that none of their past research was wrong; each of their past experiments still hold up, all the crazy DNA-sucking-and-shattering is still real, it’s just that these strategies exist in addition to sex (albeit, very infrequent sex).

Meselson and his squad begin their Sick Pape with an ominous threat that would terrify the Edward Snowdens and Chelsea Mannings among us: “Certain methods … offer definitive means for detecting infrequent or atypical sex.” [Editor’s note: What you or I do in private is not the business of the Meselson lab or the state.] However, instead of using the CIA interrogation methods implied by this terrifying abstract, they stick to modest and routine population genetics strategies. Specifically, these folks test for patterns of genetic similarity between different rotifers that imply they are the product of sexual reproduction in the not-too-distant past, and they find it.

For those who want to come into the methodological weeds with me, the “certain methods” to detect infrequent sex is this: You sequence a few genes from each of several rotifers and then look for a pattern where Gene X from rotifer 1 is very similar to its homolog in rotifer 2, whereas Gene Y is similar to its homolog in rotifer 3. This implies that there has been recent sex that has jumbled up different chromosomes between individuals in the population. To be sure that this wasn’t the result of direct DNA transfer between rotifers 1 and 3, these auteurs do the same test at several genes and show that the same pattern holds for all these genes, making it very, very unlikely to have been direct horizontal transfer of DNA.

We honor Ana Signorovitch, the pape’s first author, and her colleagues in the Meselson lab for having the courage to disprove themselves—an uncommon mark of high integrity—and for shining their beautiful light on an invisible little corner of our world. Of course, the timing and mechanisms of sex remain a complete mystery, so please keep up the hard work for many more decades to come!

Signorovitch, A., Hur, J., Gladyshev, E., & Meselson, M. (2015). Allele Sharing and Evidence for Sexuality in a Mitochondrial Clade of Bdelloid Rotifers. Genetics. doi:10.1534/genetics.115.176719

Aug. 27 2015 2:00 PM

Define “Rational”: Is That a Decoy or Your Frog Prince?

“Irrational mate choice” sounds like an accusation my mother might level at me in a terse email subject line, but in this case, it’s the title of a paper on sexual selection in the Panamanian túngara frog (Physalaemus pustulosus) published Thursday in Science magazine. In the paper, behavioral ecologists Amanda M. Lea and Michael J. Ryan report for the first time that female túngara frogs don’t always act rationally when it comes to mating—a finding that could challenge our simple understanding of this kind of mating system.

“This is the first time we’ve found evidence for irrational mating behavior,” says Lea. “If they aren’t making rational decisions, then these models don’t hold up.”

Keep in mind that, in evolutionary biology, rational doesn’t necessarily mean governed by reason (and irrational doesn’t always mean face-palmingly naive). Rather, a rational mating choice is one that conforms to an evolutionary system by which females choose their mate based on his ability to maximize her Darwinian fitness. In the animal kingdom, we expect animals to make these choices as simply, efficiently, and consistently as we choose the best value in off-brand oatmeal.

Yet in the new study, inferior suitors known as decoys—male frogs with a slower call rate*—threw a wrench in the whole “rational system” hypothesis. These decoys snuck into a group of displaying male frogs, thrusting themselves near the better options and throwing off the females’ focus. Weirdly, their presence caused the ladies to switch their initial decisions and instead go for a nearby male with a slower—less appealing—call. Talk about a bad morning after.

One explanation for the switcheroo is that female túngara frogs are easily flustered. (Decoys aren’t the only ones known to have deceived them: “I have to tell you," says Lea, "I’ve attracted many female frogs making these calls.”) You can hardly blame them. Choosing an amphibious amor is already complex enough, what with all the swelling, foaming, ribbitting, and whatnot. Adding another male to the mix, researchers speculate, could overload the female frog’s cognitive resources and cause her to make a mistake. (This confirms my opinion that grocery stores should only stock one of every option.) 

Or the mix-up might be more sinister. Decoys may intentionally create a confusing comparison, taking advantage of the kind of logic used in cognitive tests where people can’t tell that two circles are the same size because of the differently sized circles surrounding them. Similarly, dating is about comparison; the appeal of one prospect changes depending on what’s around him. With the decoy around, the female tends to prefer whatever other male is closest to it—even if he isn’t the most attractive option of the three. Think of him as a particularly ugly wingman: Next to him, the guy sitting next to him suddenly doesn’t look so bad. 

“I used to be a bartender, so this is all very familiar,” says Lea, who likes to compare her study species to human males showing off at a bar. A more modern comparison might be the world of online dating, where individuals casually scroll through prospective mates, comparing each one’s profile picture and vital stats to the one that came before it. “If the past 10 are all really really bad, you might just start to lower your threshold,” Lea says.

“I’m actually surprised no one has looked at that,” she adds. “Someone should do that study.”

The inevitable question: What’s in it for the decoy? It could be that he and the other male are engaging in a mutually beneficial friendship, whereby each takes turns acting like an inferior male to give the other a mating boost (frog bros?). In that case, they would probably be genetically related (actual bros!), so that boosting each other’s mating success would also be helping to support their own gene pool. But Lea thinks there is a likelier—and sadder—reason. 

Perhaps the decoy has no choice. After all, like the peacock, the túngara frog is a species in which the male’s sole purpose is to mate. True, even if he keeps calling, he’s probably not going to get a mate. But if he doesn’t call at all, then he definitely won’t. So no matter how spindly, how unattractive, or how woefully inadequate he may be, the decoy is doomed to just keep calling, and calling, and calling—even when there’s no one there to answer. “I’ve seen these guys die in the field mid-call,” says Lea sadly. “He’s just doing the best he can.”

Correction, Sept. 8, 2015: Rachel E. Gross originally stated that túngara frog decoys have less appealing voices. Actually, their voices are just as appealing.

Aug. 20 2015 2:02 PM

Eat the Young

In 1729, satirist Jonathan Swift proposed a sweeping solution to Ireland’s conjoined horrors of poverty, starvation, and overpopulation: Eat Irish babies. (1-year-olds, he surmised, would be equally tasty either roasted whole or baked into a pie.) Since then, murdering the youth has generally been a bit hard to sell as a social good. Yet according to ecologists in a paper published Thursday in Science, that’s exactly what we should be doing when we prey on other species.

Ecologically speaking, the role of modern humans as predators is unique: We’ve increased our killing capacity exponentially through symbiotic hunting with dogs, ever more effective weapons, and the use of fossil fuels for energy. But when researchers surveyed nearly 2,200 species across 6 continents, they found that one difference had particularly dire environmental consequences: We eat adults instead of juveniles. As a result, we tear apart food webs that have evolved over millions of years and shrink the number of animals available for human consumption in the long term.

Look at the rest of the animal kingdom, and you’ll see just how weird a strategy this is. In general, predators tend to feed on juveniles and the old or sickly; after all, they’re the easiest to catch. For instance, co-author and University of Victoria ecologist Thomas Reimchen found that predatory trout and loons in remote Canadian lakes dined almost exclusively on the juveniles (or fry) of their prey, the stickle-backed fish, while eating less than 5 percent of the adults. This strategy allowed the stickle-backs to remain at stable, healthy numbers.

By contrast, humans mainly hunt mature animals; after all, they’re larger and easier to process. Researchers found that marine fisheries take in a median rate of 14 percent—but up to a whopping 80 percent—of the biomass of adult fish. (While the fisheries example is the most dramatic, similar trends came up when they looked at data on hunting wildlife and tropical wild meat spanning back to the 1990s.) These modern practices “are especially stunning and underline just how peculiar a predator the human species has become,” says Chris Darimont, a conservation scientist at the University of Victoria and lead author on the study.

To understand why we should care about how old our prey is, it helps to understand a little more about the reproductive cycle of a fish. As fish age, they grow more fecund. And we’re not just talking about spawning one or two more eggs—adult herring can spawn hundreds of thousands of eggs a year. (Fish parents should be grateful they don't have to send their spawn to college.) Most, sadly, “are doomed from the moment they were born” due to starvation, predation, etc., says Darimont. Yet if you spawn enough, a few will, with luck, survive.

What that means for predators is that it’s generally fine to chomp up some of the plentiful wee ones. Even consuming 5 to 10 percent of those offspring—the median for most predators, according to the study—leaves plenty who will go on to become fertile adults and ensure the survival of the species. The researchers make an economic analogy, referring to the offspring as “reproductive interest” (that is, they are essentially extra, and expendable) and the adults as “reproductive capital” (the thing you want to invest in and not deplete, because they’ll make you more and more “interest” over time). Eat only the interest, and predatory cycles remain sustainable over the long term.

But that isn’t what humans do. In fact, our current ecological paradigm runs pretty much the opposite of this idea: We save the youth at the expense of the adults. Some environmental policies actually fine fishers who don’t throw juveniles back in the ocean, when those are the very fish we should be targeting. While our intentions were good—fisheries managers thought that the tossed-back small fish would then have a chance to grow up to be big fish—our predation is totally out of sync with actual ecological logic.

That isn’t the only way we’re out of sync, of course. Humans are the only species to have taken our killing to industrial levels: To feed the appetites of those across the globe, we take far more than we need, and freeze millions of pounds of seafood at sea. We ship salmon caught in Alaskan waters to New York, and fish caught in African waters to France. We engage in practices like poaching and hunting large game, making us the only predator to disrupt food chains by turning other large predators into prey. And the dark side of our mass hunting goes beyond the ecological: Fishery exploitation has led to piracy, child labor, and even slavery on fishing vessels.

So we should kill fewer adults, and target juveniles instead—but at sustainable quotas, based on the natural quotas we see in other predators. Such a sea change, says Reimchen, wouldn’t be difficult. “There’s all sorts of simple, technical solutions”—including using flexible hooks or lobster traps that target smaller animals specifically—“that can help us shift away from the reproductive capital,” he says. “We could do it without much difficulty.” We may be the world’s top predator, but when it comes to sustainable predation, it turns out we have a lot to learn.

Aug. 19 2015 9:06 AM

Hummingbirds Are Fierce, Deadly Gods of War

Hummingbirds seem to be composed of equal parts bumblebee and electron, and they sport coats of iridescent feathers so fetching, you’d think every day was Fat Tuesday. They’re the world’s smallest birds, weighing less than nickels do, and they just seem so, well, adorable. But the Aztecs had a rather different view of these birds.

According to legend, the earth goddess Coatlicue once picked up a bundle of hummingbird feathers that had fallen from the sky. Storing them near her bosom, she became with child. This angered Coatlicue’s other 400 children, so they conspired to kill her—but the moment they did, a fully grown, heavily armed, and mad as hell Huitzilopochtli sprang from her womb and started cutting off heads.  

Huitzilopochtli is the Aztec god of war and the sun. He is depicted either as a hummingbird itself, or as a warrior with hummingbird feathers on his helmet. When Aztec high priests cut out the hearts of enemies and slaves, it was to honor and feed the hummingbird god. (If Huitzilopochtli was happy and fed, the Aztecs would be triumphant in war and conquest.)

As a symbol of their connection to Huitzilopochtli, Aztec kings were fashioned with cloaks made entirely of hummingbird skins. Imagine the way such a garment would shimmer in the sun, especially given the way hummingbird feathers reflect and refract light to create otherworldly waves of colors. (If you’re wondering how many hummingbirds it would take to make an adult-size cloak … good question. About 8,000.)

Aztec origin myths aside, hummingbirds really are badasses. And there’s a biological reason why: Their lives depend on it.

You probably already know that hummingbirds can perform all sorts of crazy flight maneuvers, like hovering in place and flying backward and even upside down. The little dudes have no problem drinking nectar out of a revolving feeder.  

These acrobatics push the animal’s body to the absolute metabolic limit for vertebrates. Every day in the life of the hummingbird is spent between the ruin of overexertion and the reward of nectar won. To make matters worse, they have a very low capacity for storing energy, and their small body size makes it difficult to stay warm. When it’s cold at night, some species have to go into torpor, a hibernationlike state. “They basically couldn’t survive eight hours without food or fuel if they were at their regular metabolism,” says Geoff LeBaron of the National Audubon Society.

There are more than 320 species of hummingbirds from Alaska to southern Chile—they’re strictly New World birds. They range in size and diet, but you can generally estimate that a hummingbird will eat between 1½ to 3 times its own body weight in nectar each day. And that nectar is chock-full of sugar. Scientists estimate that the average hummer eats about half its body weight in sugar each day. (Yes, hummer is an accepted term for hummingbirds. Get over it.)

According to my rough math, that’d be like a 200-pound adult human drinking 1,163 cans of Coca-Cola each day. (If you’re a Pepsi person, it’d be slightly fewer—1,106 cans per day—because Pepsi is more sugary than Coke.)

Anyway, to make this constant nom-nomming possible, hummingbirds come equipped with excellent spatial and temporal memory. They not only know where the nectar sources are within a given territory but how good they are and when they’ll become available, says Paulina González-Gómez, a research associate at University of California, Davis. If you take a feeder down and see a hummingbird hovering near the spot and think it’s glaring at you, it’s not your imagination.

Males take all of this to the next level by establishing and defending territories. They’ll throw down with rival males, females, and their own reflection in a window. They’re also not above telling a bee to buzz off by giving it a quick flick of the beak or chasing a much larger bird out of their flower patch.

When hummingbirds fight each other, it usually involves chases and vocalizations meant to scare or simply harass the intruder until it goes away. Sometimes, these encounters escalate to grappling each other with their claws, though you’d need a high-speed camera to catch it. Sometimes, LeBaron says, fatal collisions can occur.

“It’s not that their aim is to kill,” he says, “but they can impale each other, and then that’s the end.”

At least one species of hummingbird, Phaethornis longirostris, actually has a beak designed to be a weapon. A study published last year by some of González-Gómez’s collaborators found that the beaks of adult males were like stilettos, longer and pointier than those of juvenile males or females—the better for stabbing other males in the throat.

“I'd say that if hummingbirds were ostrich-size birds they would be extremely dangerous,” says González-Gómez.

Interestingly, there’s a saturation point at which most aggression ceases. You can see it on display at any flower garden or aviary where there are more nectar sources than one hummingbird could reasonably defend. But the point is, he doesn’t need to. Hummingbird aggression costs a ridiculous amount of energy. If there’s a surplus of food, it’s pointless wasting energy trying to defend it.

Aggression may also play into mating success for the males. Another study by González-Gómez found that higher levels of testosterone were positively related with body condition in Anna’s hummingbirds. González-Gómez says this could mean aggression is linked to mating success, since better-defended territories lead to healthier males, which would in theory be more attractive to females. However, the relationship between testosterone and body condition was less pronounced in other species, indicating that other factors play a role.

Researchers are still determining just how all this sugar-rage fits into the birds’ life history, but it’s obvious that the male hummingbird is disproportionately confident for his size.

LeBaron says he once saw a male hummingbird harass and sort of chase a golden eagle. “Which seems a little over the top,” he laughed. A screaming-freakin’-eagle vs. a bird about the size and weight of a Dum Dums lollipop.

No wonder the Aztecs believed warriors cut down in battle would be reincarnated as hummingbirds—ounce for ounce, there’s probably no fiercer creature on Earth. And to think, you can lure these little war gods to your porch with nothing more than a red feeder and a little sugar water.