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Ravens Can Hold Grudges for Weeks, Study Finds

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Never cross a corvid. Crows have been known to hold grudges, and research says that ravens do, too. A new study in Animal Behavior spotted by The Verge finds that ravens remember the nature of their interactions with humans and can remember how the experience went for up to a month afterward.

The study, which was conducted by researchers at the University of Vienna and Lund University in Sweden, presented ravens with two types of interactions with human experimenters: some that could be considered fair and others unfair.

The nine ravens had all been hand-raised in captivity by humans. (The paper delightfully includes their names, which are: Laggie, Tom, Nobel, George, Horst, Louise, Joey, Rocky, and Paul.) The birds were trained to exchange a low-quality food (bread) for something they liked more (cheese). The ravens had to take a risk in giving the human their snack, though. They could give away the bread and receive cheese in return, but there was always the chance that they would give away their bread and not get anything back.

In the experiment, each bird was given many opportunities to exchange its bread pieces with a human trainer. Another bird looked on, but couldn't participate. In some sessions, the participating bird interacted with a person who always gave them cheese in exchange for their bread. In other sessions, they interacted with a person who took their bread but ate the cheese themselves—an unfair exchange.

Later, the researchers tested whether the birds would show a preference for the person who had always been fair in their interactions. A month later, eight of the nine birds chose to trade with the experimenter who had previously shown themselves to be fair in their interactions over an experimenter who had cheated them in the past (the ninth chose a third, neutral experimenter). However, this only applied to the birds’ first-hand experiences. The birds who observed another bird’s fair or unfair interactions as a third party did not seem to remember who could be trusted and who could not.

Considering crows’ abilities to remember the people who slight them, it’s not terribly surprising that their raven cousins would be able to, too. Nor is it their only complex skill: Corvids can also use tools and practice self-control. Both of which should worry you if you make a habit of making ravens and crows mad.

[h/t The Verge]

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How Bats Protect Rare Books at This Portuguese Library
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Visit the Joanina Library at the University of Coimbra in Portugal at night and you might think the building has a bat problem. It's true that common pipistrelle bats live there, occupying the space behind the bookshelves by day and swooping beneath the arched ceilings and in and out of windows once the sun goes down, but they're not a problem. As Smithsonian reports, the bats play a vital role in preserving the institution's manuscripts, so librarians are in no hurry to get rid of them.

The bats that live in the library don't damage the books and, because they're nocturnal, they usually don't bother the human guests. The much bigger danger to the collection is the insect population. Many bug species are known to gnaw on paper, which could be disastrous for the library's rare items that date from before the 19th century. The bats act as a natural form of pest control: At night, they feast on the insects that would otherwise feast on library books.

The Joanina Library is famous for being one of the most architecturally stunning libraries on earth. It was constructed before 1725, but when exactly the bats arrived is unknown. Librarians can say for sure they've been flapping around the halls since at least the 1800s.

Though bats have no reason to go after the materials, there is one threat they pose to the interior: falling feces. Librarians protect against this by covering their 18th-century tables with fabric made from animal skin at night and cleaning the floors of guano every morning.

[h/t Smithsonian]

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Honey Bees Can Understand the Concept of Zero
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The concept of zero—less than one, nothing, nada—is deceptively complex. The first placeholder zero dates back to around 300 BCE, and the notion didn’t make its way to Western Europe until the 12th century. It takes children until preschool to wrap their brains around the concept. But scientists in Australia recently discovered a new animal capable of understanding zero: the honey bee. According to Vox, a new study finds that the insects can be taught the concept of nothing.

A few other animals can understand zero, according to current research. Dolphins, parrots, and monkeys can all understand the difference between something and nothing, but honey bees are the first insects proven to be able to do it.

The new study, published in the journal Science, finds that honey bees can rank quantities based on “greater than” and “less than,” and can understand that nothing is less than one.

Left: A photo of a bee choosing between images with black dots on them. Right: an illustration of a bee choosing the image with fewer dots
© Scarlett Howard & Aurore Avarguès-Weber

The researchers trained bees to identify images in the lab that showed the fewest number of elements (in this case, dots). If they chose the image with the fewest circles from a set, they received sweetened water, whereas if they chose another image, they received bitter quinine.

Once the insects got that concept down, the researchers introduced another challenge: The bees had to choose between a blank image and one with dots on it. More than 60 percent of the time, the insects were successfully able to extrapolate that if they needed to choose the fewest dots between an image with a few dots and an image with no dots at all, no dots was the correct answer. They could grasp the concept that nothing can still be a numerical quantity.

It’s not entirely surprising that bees are capable of such feats of intelligence. We already know that they can count, teach each other skills, communicate via the “waggle dance,” and think abstractly. This is just more evidence that bees are strikingly intelligent creatures, despite the fact that their insect brains look nothing like our own.

Considering how far apart bees and primates are on the evolutionary tree, and how different their brains are from ours—they have fewer than 1 million neurons, while we have about 86 billion—this finding raises a lot of new questions about the neural basis of understanding numbers, and will no doubt lead to further research on how the brain processes concepts like zero.

[h/t Vox]

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