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Hippos Eat Way More Meat than We Thought, and It Can Make Them Sick

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Hippos are huge animals with fearsome tusks and aggressive natures, but they mainly eat plants. Sometimes they attack people and can tangle with crocodiles, sure, but they’re not predators or carnivores. Right?

But a closer look reveals that hippos aren't so herbivorous after all, says biologist Joseph Dudley. Despite their grass-heavy diets and all the adaptations that make them great grazers, hippos have been known to eat their fair share of meat. There are scattered reports by scientists and amateur observers (note: NSFW gory pictures) of hippos attacking, killing, and eating other animals, stealing kills from predators, and scavenging carcasses, including those of other hippos. In a new paper published in the journal Mammal Review, Dudley and his fellow researchers argue that these incidents aren’t as unusual as they seem or isolated to a few animals or populations. They say there’s a pattern of carnivorous behavior in hippo populations across the animal’s entire range—and that behavior has consequences for hippos. 

Evolution has outfitted hippos and other big herbivores for a plant-based diet, and their guts and the microbes that live within them are adapted for fermenting and digesting lots of plant material. That doesn’t mean these herbivores animals can’t add meat to their menu, though. Many can and do. Antelope, deer, and cattle have been known to feed on carrion, birds’ eggs, birds, small mammals, and fish. What might hold most of these animals back from more frequent carnivory, Dudley suggests, isn’t their digestive physiology, but “biomechanical limitations” in securing and ingesting meat. In other words, they aren’t built for taking down prey or biting into flesh. The hippo is another story. 

THOSE WHO CAN, DO

“Due to its large body size and unusual mouth and dental configurations, the hippo may represent an extreme case in which the predation and scavenging of large mammals by an ungulate species is not constrained by biomechanical factors,” Dudley and his team write. Not only can hippos kill and eat other big animals more easily than other herbivores, the researchers say, the fact that they’re territorial and highly aggressive may facilitate carnivory, putting them in situations where they kill other animals and can get themselves something to eat.

And eat they do. Since Dudley made the first scientific record of carnivory in hippos in 1996, other cases of hippo carnivory and even cannibalism have also been documented. Dudley lists instances where wild hippos have fed on impalas, elephants, kudus, wildebeest, zebras, and other hippos that they either killed themselves or were killed by other predators. Events like these have been seen both during times when carnivory may be a last resort (e.g. droughts when food is scarce), and when it was merely a convenient opportunity, like a mass drowning of wildebeest crossing a river. There are also reports of captive hippos in zoos killing and eating their neighbors, including tapirs, wallabies, flamingoes and pygmy hippos.

“Our scientific records, coupled with those of other investigators and observers, demonstrate that the phenomenon of carnivory by hippos is not restricted to particular individuals or local populations but is an inherent characteristic of the behavioral ecology of hippos,” the team writes.

EATING MEAT WHILE WE SLEEP

If that’s the case, then why did it take so long for anyone to figure it out? Part of the blame can fall on conflicting schedules. Hippos are mostly active at night, which means their meals, meat or otherwise, usually go unseen by humans. Their carnivorous ways, Dudley thinks, have simply been overlooked. 

They may also explain why hippos are so susceptible to anthrax and experience higher mortality rates during outbreaks, the researchers say. Hippos, they think, are doubly exposed to the disease because they ingest and inhale bacterial spores on plants and in the soil like other herbivores, and also consume them when feeding on contaminated carcasses. Cannibalism during outbreaks exacerbates the problem. 

That carnivory might make these outbreaks worse in hippo populations has implications for controlling the disease and protecting both animals and humans. During anthrax outbreaks among wildlife, many human illnesses occur because of contaminated “bush meat.” During a 2011 outbreak in Zambia, for example, 511 human cases of anthrax and at least five deaths were linked to people handling and consuming meat from infected hippos. Burying or burning suspected infected animal carcasses is a standard practice during anthrax outbreaks, and the researchers think that this may be especially effective in hippo habitats because it takes infected meat off the menu for both humans and hippos. 

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Slow Motion Is the Only Way to Appreciate a Chameleon’s Lightning-Fast Tongue
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From the unusual way they walk, to their ability to change color, the evolutionary adaptations of chameleons are pretty bizarre, and some of them remain mysterious even to scientists. Their super-powered tongues, for instance, can dart out so quickly that the movement can barely be seen with the naked eye. But modern high-speed cameras have enabled researchers at the University of South Dakota to observe this appendage at work like never before. The video below, shared over at The Kid Should See This, includes some of that groundbreaking footage, and it's pretty amazing to watch.

Shooting at 3000 frames per second, the camera was able to capture every split-second aspect of the chameleon's tongue strike. Slowed down, the video allows you to see how every component of the process works in harmony: First, muscles in the lizard’s tongue contract like the string of a bow. Then, when that tension is released, the bony base of the tongue shoots forward, pushing the sticky, elastic part toward the chameleon’s prey.

According to Christopher Anderson, one of the scientists who conducted the high-speed camera research, larger chameleons can catapult their tongues forward at distances of one to two times their body length. For smaller chameleons, this distance can reach up to two and a half times their body length. “Small chameleons need to be able to eat more food for their body size than large chameleons,” he tells bioGraphic in the video, “and so by being able to project their tongues proportionately further than these large species, they basically are opening up additional feeding opportunities to themselves that they wouldn’t have if they had a shorter tongue.”

To see one of nature’s greatest hunting tools in action, check out the full video below.

[h/t The Kid Should See This]

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There May Be an Ancient Reason Why Your Dog Eats Poop
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Dogs aren't known for their picky taste in food, but some pups go beyond the normal trash hunting and start rooting around in poop, whether it be their own or a friend's. Just why dogs exhibit this behavior is a scientific mystery. Only some dogs do it, and researchers aren't quite sure where the impulse comes from. But if your dog is a poop eater, it's nearly impossible to steer them away from their favorite feces.

A new study in the journal Veterinary Medicine and Science, spotted by The Washington Post, presents a new theory for what scientists call "canine conspecific coprophagy," or dogs eating dog poop.

In online surveys about domestic dogs' poop-eating habits completed by thousands of pet owners, the researchers found no link between eating poop and a dog's sex, house training, compulsive behavior, or the style of mothering they received as puppies. However, they did find one common link between the poop eaters. Most tended to eat only poop that was less than two days old. According to their data, 85 percent of poop-eaters only go for the fresh stuff.

That timeline is important because it tracks with the lifespan of parasites. And this led the researchers to the following hypothesis: that eating poop is a holdover behavior from domestic dogs' ancestors, who may have had a decent reason to tuck into their friends' poop.

Since their poop has a high chance of containing intestinal parasites, wolves poop far from their dens. But if a sick wolf doesn't quite make it out of the den in time, they might do their business too close to home. A healthier wolf might eat this poop, but the parasite eggs wouldn't have hatched within the first day or two of the feces being dropped. Thus, the healthy wolf would carry the risk of infection away from the den, depositing the eggs they had consumed away in their own, subsequent bowel movements at an appropriate distance before the eggs had the chance to hatch into larvae and transmit the parasite to the pack.

Domestic dogs may just be enacting this behavior instinctively—only for them, there isn't as much danger of them picking up a parasite at home. However, the theory isn't foolproof. The surveys also found that so-called "greedy eaters" were more likely to eat feces than dogs who aren't quite so intense about food. So yes, it could still be about a poop-loving palate.

But really, it's much more pleasant to think about the behavior as a parasite-protection measure than our best pals foraging for a delicious fecal snack. 

[h/t The Washington Post]

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