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Why Do Brood V Cicadas Spend 17 Years Underground?

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In 1999, the cicadas of Brood V emerged in parts of Maryland, Ohio, Pennsylvania, Virginia, West Virginia, and New York, and then disappeared almost as quickly as they came, leaving only their eggs and molted exoskeletons behind. Once the eggs hatched, the new generation of cicada nymphs crawled underground, where they’ve spent the past 17 years biding their time and living off of fluid from tree roots.

Sometime this week, when the time is right and the soil is warm, they’ll emerge again to molt, enter their adult stage, mate, make a lot of noise, and lay their own eggs. (Brood V was due to emerge sooner, but scientists say the cool spring has delayed them.)

Not all cicadas play this long game of hide-and-seek. Most North American species are “annual cicadas” whose broods emerge every summer and have unsynchronized, two-to-five-year life cycles. Only a handful of species are “periodical cicadas” that have longer, synchronized life cycles, bursting forth together in huge broods every 13 or 17 years.

Seventeen years is a long time to hang out underground. Why do these cicadas spend so much time out of sight and out of mind? And why do they come out all at once?

Periodical cicadas have had scientists scratching their heads for centuries. As one team of researchers explained, “We do not know the answers to these questions but experimental evidence and mathematical models have enabled us to develop some ideas.”

One explanation for the cicadas’ long development times is that the 13- and 17-year cycles keep broods in the same region from emerging at the same time or too quickly after each other, which minimizes competition for resources and prevents interbreeding.

Another idea is that the cycles protect the cicadas from predators and parasites with shorter life cycles. Biologist Stephen Jay Gould explained it like this:

“They are large enough to exceed the life cycle of any predator, but they are also prime numbers (divisible by no integer smaller than themselves). Many potential predators have 2–5 year life cycles. Such cycles are not set by the availability of periodical cicadas (for they peak too often in years of nonemergence), but cicadas might eagerly be harvested when the cycles coincide. Consider a predator with a cycle of five years; if cicadas emerged every 15 years, each bloom would be hit by the predator. By cycling at a large prime number, cicadas minimize the number of coincidences (every 5X17, or 85 years, in this case).”

Staying out of sync with predators’ life cycles keeps the cicadas from becoming a reliable source of food. (It also prevents the predators from adapting or devising better ways of feeding on the cicadas.) This hypothesis is difficult to test because cicada emergences are so far apart, but mathematical models developed by researchers support the idea.

The long cycles might also be the result of North America’s prehistoric climate. Periodical cicadas evolved during a time when glaciers advanced and retreated over what is now the eastern U.S. Temperatures would have been unpredictably warm or cool and often too low for the insects to fly or mate. When researchers calculated the chances of survival for cicadas with different life cycles in this kind of climate, they found that the longer the insects stayed underground, the lower the chance they’d emerge during a too-cool summer. Over time, the scientists suggest, insects with shorter cycles died out, while those who by chance took longer to develop survived and reproduced.

There are other explanations for the broods’ impressive synchronization and overwhelming numbers. Some scientists suggest that high population densities are necessary to produce the deafening choruses that males use to attract mates. Another idea is that there’s safety in numbers. Cicadas don’t have much in the way of defenses, but when billions emerge at the same time, there are simply too many for predators to eat them all. Even after birds and other animals have had their fill, there are plenty of cicadas left to mate, lay eggs, and start the 17-year process yet again.

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Animals
Pigeons Are Secretly Brilliant Birds That Understand Space and Time, Study Finds
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Of all the birds in the world, the pigeon draws the most ire. Despite their reputation as brainless “rats with wings,” though, they’re actually pretty brilliant (and beautiful) animals. A new study adds more evidence that the family of birds known as pigeons are some of the smartest birds around, as Quartz alerts us.

In addition to being able to distinguish English vocabulary from nonsense words, spot cancer, and tell a Monet from a Picasso, pigeons can understand abstract concepts like space and time, according to the new study published in Current Biology. Their brains just do it in a slightly different way than humans’ do.

Researchers at the University of Iowa set up an experiment where they showed pigeons a computer screen featuring a static horizontal line. The birds were supposed to evaluate the length of the line (either 6 centimeters or 24 centimeters) or the amount of time they saw it (either 2 or 8 seconds). The birds perceived "the longer lines to have longer duration, and lines longer in duration to also be longer in length," according to a press release. This suggests that the concepts are processed in the same region of the brain—as they are in the brains of humans and other primates.

But that abstract thinking doesn’t occur in the same way in bird brains as it does in ours. In humans, perceiving space and time is linked to a region of the brain called the parietal cortex, which the pigeon brains lack entirely. So their brains have to have some other way of processing the concepts.

The study didn’t determine how, exactly, pigeons achieve this cognitive feat, but it’s clear that some other aspect of the central nervous system must be controlling it. That also opens up the possibility that other non-mammal animals can perceive space and time, too, expanding how we think of other animals’ cognitive capabilities.

[h/t Quartz]

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The Queen's Racing Pigeons Are in Danger, Due to an Increase in Peregrine Falcons
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Queen Elizabeth is famous for her love of corgis and horses, but her pet pigeons don't get as much press. The monarch owns nearly 200 racing pigeons, which she houses in a luxury loft at her country estate, Sandringham House, in Norfolk, England. But thanks to a recent boom in the region’s peregrine falcon population, the Queen’s swift birds may no longer be able to safely soar around the countryside, according to The Telegraph.

Once endangered, recent conservation efforts have boosted the peregrine falcon’s numbers. In certain parts of England, like Norfolk and the city of Salisbury in Wiltshire, the creatures can even find shelter inside boxes installed at local churches and cathedrals, which are designed to protect potential eggs.

There’s just one problem: Peregrine falcons are birds of prey, and local pigeon racers claim these nesting nooks are located along racing routes. Due to this unfortunate coincidence, some pigeons are failing to return to their owners.

Pigeon racing enthusiasts are upset, but Richard Salt of Salisbury Cathedral says it's simply a case of nature taking its course. "It's all just part of the natural process,” Salt told The Telegraph. "The peregrines came here on their own account—we didn't put a sign out saying 'room for peregrines to let.' Obviously we feel quite sorry for the pigeons, but the peregrines would be there anyway."

In the meantime, the Queen might want to keep a close eye on her birds (or hire someone who will), or consider taking advantage of Sandringham House's vast open spaces for a little indoor fly-time.

[h/t The Telegraph]

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