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How Some Birds Evolved to Build Protected Nests

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Birds' nests are as diverse as the creatures who build them. The variety of locations, shapes, and sizes they’re built in and the materials they’re made from can be staggering. Hamerkops, for example, spend weeks assembling thousands of twigs into a massive nest that’s insulated and waterproofed with mud. Then there’s the horned coot, which makes its nest on top of an island of pebbles that it piles up in shallow lakes. Meanwhile, the edible-nest swiftlet builds its home entirely from hardened layers of its own saliva.

Even for someone more focused on birds’ brains, like neurobiologist Zach Hall was during his Ph.D. work, the diversity of nests didn’t go unnoticed—nor did the fact that the evolution of such wildly different nest types isn’t well researched. With a new study, Hall thinks he’s figured out how one variety of nest, a protected dome-shaped one, evolved. As they say in real estate, it’s all about location, location, location, and dome nests appear to have evolved as some birds transitioned from nesting in trees to nesting on or near the ground and needed a different kind of nest more suited to the new terrain. 

It’s not exactly a new idea, Hall says. Biologist Nicholas Collias suggested it nearly 20 years ago to explain why some some birds from a family called the Old World babblers build dome nests while others build open, cup-shaped ones. At the time, though, Collias didn’t have enough information or the right techniques to test his hypothesis. With a more complete picture of babblers’ evolutionary history and relationships now available, Hall and his team decided to see if the idea held up. 

The researchers gathered descriptions of the nests built by 155 different species of babbler and mapped their heights and structures (either cup- or dome-shaped) to the birds’ family tree. They found that Collias was on to something. Across the babbler family, species that build dome nests live closer to the ground than their cup-building relatives, and as the birds diverged from ancestors that built cup-shaped nests high in the trees, dome-shaped nests coevolved with nest height as some species ventured closer to the ground.

While they confirmed that nest height and structure go hand in hand, the researchers are still left with the question of which trait arose first and influenced the other. Nesting closer to the ground could have driven some species to add domes to their nests for protection against predators, as Collias suggested (though the team says it can’t yet rule out other influences, like parasites or the need to keep nests warm on shady forest floors), but the domes might have also come first and allowed the species that built them to stake out new nesting sites. The team notes, though, that the first situation is more likely. Changing nest height is an easier leap than changing nest shape, and more consistent with what researchers have seen in other birds. 

There’s still more work to be done, but Hall’s team is confident that their approach can answer the remaining questions about babblers and be used with other birds to uncover the reasons they build their nests they way they do.

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Good News, Dog Parents: You Can Teach Puppies as Well as Their Canine Moms Can
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If you’ve ever adopted a puppy, you probably know how frustrating it can be to teach your new family member the basic tenets of common decency, like not to pee on the carpet or tear up a whole roll of toilet paper.

In other areas, though, pups are rather impressive learners, capable of mimicking some human behaviors. In fact, for some tasks, they learn just as effectively from watching people as they do from watching other dogs, including their own mothers, a new study in Nature revealed.

Researchers from Hungary and the UK took 48 young puppies of various breeds and studied the conditions under which they can be taught to open a puzzle box containing food. The experiment revealed that the puppies were able to learn how to open the box regardless of whether the task was first demonstrated by a person, their mother, or an unfamiliar dog. In other words, not only are puppies capable of social learning, but they're able to learn tasks from humans they don't know—in this case, the experimenter.

However, researchers were surprised to learn that the puppies were more likely to learn how to open the box by watching an unfamiliar dog than by watching their own mothers. That may be because puppies spend more time looking at—and thus, learning from—an unfamiliar dog that intrigues them. This differs from other species such as kittens, which “learn to press a lever for food more rapidly from their mother than from an unfamiliar adult,” the study notes.

In addition, the puppies were able to perform the task again after a one-hour break, indicating that they had retained some memory of the learning experience.

The ability of dogs to learn from humans has been recorded in previous research. A 2015 study revealed that dogs learn better by demonstration (or the “do as I do” method) than training techniques that involve a system of punishments and rewards. The "do as I do" approach probably isn't the most practical method of teaching your pup to do its business outside, but if you already have an adult dog at home, your new puppy can follow the older dog's lead and learn by example.

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Michael Hutchinson
Spiders Can Fly Through the Air Using the Earth's Electric Field
A spider exhibiting ballooning behavior.
A spider exhibiting ballooning behavior.
Michael Hutchinson

Every so often, otherwise Earth-bound spiders take to the air. Ballooning spiders can travel hundreds of miles through the air (and, horrifyingly, rain down on unsuspecting towns). The common explanation for this phenomenon is that the spiders surf the wind on strands of silk, but there may be other forces at work, according to a new study spotted by The Atlantic.

In the research, published in Current Biology, University of Bristol scientists argue that Earth's atmospheric electricity allows spiders to become airborne even on windless days. To test their hypothesis, the researchers exposed spiders in the lab to electric fields similar to those naturally found in the atmosphere.

When the electric field was turned on, the spiders began to exhibit behavior associated with ballooning—they "tiptoed" on the ends of their legs, raised their abdomens, and released silk. Spiders only exhibit this behavior when ballooning. And when they did become airborne, the spiders’ altitude could be controlled by turning the electric field on and off. When the electric field was on, they rose through the air, but when it was off, they drifted downward.

This provides a potential explanation for why spiders take to the skies on certain days but not others, and how they can fly in calm, windless weather— something scientists have puzzled over since the early 19th century. (Even Darwin was flummoxed, calling it "inexplicable," The Atlantic notes.) However, the researchers note that these electric fields might not be totally necessary for ballooning—wind alone might work perfectly fine on some days, too. But understanding more about when and how spiders become airborne could help us predict when there will be large masses of arachnids flying through the skies (and hide).

[h/t The Atlantic]

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