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Wikimedia Commons

Some Birds Benefit From Having Parasites

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Wikimedia Commons

Cuckoos are some of nature’s most practiced—and successful—con artists. Many species from this large family of birds are brood parasites. They lay their eggs in the nests of other birds and outsource the raising of their chicks to these foster parents, whose own babies are often murdered by the new arrivals. Even when the cuckoo doesn’t defenestrate its adoptive siblings, it usually outcompetes them for food and parental care. So they're typically lousy house guests—but scientists now think that hosting a murderous freeloader might have some benefits, too. 

Because of the costs of caring for them, many cuckoo hosts have developed defenses against them, like recognizing and evicting alien eggs or mobbing adult cuckoos when they try to sneak their eggs in. In northern Spain, carrion crows are plagued by great spotted cuckoos. More than two thirds of their nests are parasitized, but the crows don’t drive the cuckoos out. The cuckoo chicks leave their foster siblings alone as well, and they’re raised alongside each other without many problems. Even though they have to share food and attention from mom and dad, the crow chicks in parasitized nests don’t seem to be in any worse condition than ones that grow up cuckoo-free. 

Sometimes birds don’t defend their nests because cuckoos are a relatively new problem, but the crows and cuckoos have been neighbors for ages. Biologist Daniela Canestrari wondered if the crows instead keep the cuckoos around because they get something out of it. 

Canestrari has spent more than a decade studying crows in Europe, and long-term data from her years of crow studies showed that eggs in both parasitized and nonparasitized nests had roughly the same chance of hatching. Once the chicks were born, the parasitized nests were more successful (that is, more likely to produce at least one crow fledgling) than the ones without cuckoos.

To see if there was a benefit to getting saddled with another bird’s chicks, Canestrari and her team tracked four different kinds of crow nests: 14 ones that they’d transferred cuckoo hatchlings to; 16 ones they’d removed hatchlings from; and 28 parasitized and 24 non-parasitized ones that they left alone to serve as controls. The chick-shuffling experiment suggested a direct link between cuckoo chicks and the success of a nest. The nests that had their cuckoo chicks removed failed more than any of the others, including the controls, while the ones that had cuckoos added to them were the most successful of all the nests. 

So how do cuckoo chicks help crows when all they do is sit around and take free meals? Jostle a great spotted cuckoo and you’ll find out. When the chicks are harassed, they secrete a foul-smelling goo from their cloaca (a bird’s entrance and exit for mating and getting rid of waste) that’s loaded with “caustic and repulsive” ingredients like acids and sulfurous compounds. It’s not something you want around your mouth or nose, and the researchers thought that it might scare predators away from the nests. When they offered bits of meat covered with either cuckoo secretions or plain water to feral cats, falcons and other crows (the three main groups that prey on crow nests), the predators overwhelmingly rejected the one with the cuckoo goo.

Canestrari’s study area was home to plenty of predators, which cause the failure of anywhere from a quarter to three-quarters of the crows’ breeding attempts each year. As much of a pain as a cuckoo can be sometimes, any help a crow can get keeping all these predators at bay might be worth the hassle of taking care of someone else’s kids. The benefit only comes when the cuckoo actually has predators to repel, though. In years with overall low rates of predation and nest failure, cuckoo-parasitized nests were less successful than they were during times with more attacks from predators. 

The line between friend and foe, or parasite and protector, isn’t always as cleanly drawn as it seems. As the shifting relationships between crow and cuckoo show, a lot depends on context and sometimes even the most obnoxious nest mates are nice to have around. 

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Big Questions
Why Do Cats Freak Out After Pooping?
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Cats often exhibit some very peculiar behavior, from getting into deadly combat situations with their own tail to pouncing on unsuspecting humans. Among their most curious habits: running from their litter box like a greyhound after moving their bowels. Are they running from their own fecal matter? Has waste elimination prompted a sense of euphoria?

Experts—if anyone is said to qualify as an expert in post-poop moods—aren’t exactly sure, but they’ve presented a number of entertaining theories. From a biological standpoint, some animal behaviorists suspect that a cat bolting after a deposit might stem from fears that a predator could track them based on the smell of their waste. But researchers are quick to note that they haven’t observed cats run from their BMs in the wild.

Biology also has a little bit to do with another theory, which postulates that cats used to getting their rear ends licked by their mother after defecating as kittens are showing off their independence by sprinting away, their butts having taken on self-cleaning properties in adulthood.

Not convinced? You might find another idea more plausible: Both humans and cats have a vagus nerve running from their brain stem. In both species, the nerve can be stimulated by defecation, leading to a pleasurable sensation and what some have labeled “poo-phoria,” or post-poop elation. In running, the cat may simply be working off excess energy brought on by stimulation of the nerve.

Less interesting is the notion that notoriously hygienic cats may simply want to shake off excess litter or fecal matter by running a 100-meter dash, or that a digestive problem has led to some discomfort they’re attempting to flee from. The fact is, so little research has been done in the field of pooping cat mania that there’s no universally accepted answer. Like so much of what makes cats tick, a definitive motivation will have to remain a mystery.

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Watch a School of Humpback Whales 'Fish' Using Nets Made of Bubbles 

Just like humans, humpback whales catch many fish at once by using nets—but instead of being woven from fibers, their nets are made of bubbles.

Unique to humpbacks, the behavior known as bubble-net feeding was recently captured in a dramatic drone video that was created by GoPro and spotted by Smithsonian. The footage features a school of whales swimming off Maskelyne Island in British Columbia, Canada, in pursuit of food. The whales dive down, and a large circle of bubbles forms on the water's surface. Then, the marine mammals burst into the air, like circus animals jumping through a ring, and appear to swallow their meal.

The video offers a phenomenal aerial view of the feeding whales, but it only captures part of the underwater ritual. It begins with the group's leader, who locates schools of fish and krill and homes in on them. Then, it spirals to the water's surface while expelling air from its blowhole. This action creates the bubble ring, which works like a net to contain the prey.

Another whale emits a loud "trumpeting feeding call," which may stun and frighten the fish into forming tighter schools. Then, the rest of the whales herd the fish upwards and burst forth from the water, their mouths open wide to receive the fruits of their labor.

Watch the intricate—and beautiful—feeding process below:


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