Wikimedia Commons
Wikimedia Commons

Some Birds Benefit From Having Parasites

Wikimedia Commons
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. 

10 Notable Gestation Periods in the Animal Kingdom

The gestation periods of the animal kingdom are varied and fascinating. Some clock in at just a few weeks, making any human green with envy, while others can last more than a year. Here are 10 notable gestation times for animals around the globe. The lesson? Be thankful that you’re not a pregnant elephant.

1. ELEPHANTS: 640-660 DAYS

Elephants are pregnant for a long time. Like really, really long. At an average of 95 weeks, the gestation period is more than double the length of a human pregnancy, so it shouldn't come as a shock that female elephants don't often have more than four offspring during their lifetimes. Who has the time?


A photo of a mother hippo and her baby in Uganda

Yes, it takes less time to make a hippopotamus than it takes to make a human.


Baby giraffes can weigh more than 150 pounds and can be around 6 feet tall. Another fascinating tidbit: giraffes give birth standing up, so it's pretty normal for a baby to fall 6 feet to the ground.


There’s a reason for the long wait: after that 17 months, Baby Shamu emerges weighing anywhere from 265 to 353 pounds and measuring about 8.5 feet long. Yikes.

5. OPOSSUM: 12-13 DAYS

A baby opossum wrapped up in a blanket

Blink and you'll miss it: This is the shortest gestation period of any mammal in North America. But since the lifespan of an opossum is only two to four years, it makes sense.


Hey, they get off pretty easy.


It's not a huge surprise that their gestational periods are pretty similar to ours, right?


A pair of black bear cubs

Also less than a human. Interestingly, cubs might only be 6 to 8 inches in length at birth and are completely hairless. 


This is the longest gestation period of any rodent. Thankfully for the mother, porcupine babies (a.k.a. porcupettes) are actually born with soft quills, and it's not until after birth that they harden up.


Baby walruses? Kind of adorable. They certainly take their sweet time coming out, though.

Goldfish Can Get Depressed, Too

Don’t believe what Pixar is trying to sell you: Fish are not exactly brimming with personality. In aquariums, they tend to swim in circles, sucking up fragments of food and ducking around miniature treasure chests. To a layperson, fish don’t appear to possess concepts of happy, or sad, or anything in between—they just seem to exist.

This, researchers say, is not quite accurate. Speaking with The New York Times, Julian Pittman, a professor at the Department of Biological and Environmental Sciences at Troy University, says that fish not only suffer from depression, they can be easily diagnosed. Zebrafish dropped into a new tank who linger at the bottom are probably sad; those who enthusiastically explore the upper half are not.

In Pittman’s studies, fish depression can be induced by getting them “drunk” on ethanol, then cutting off the supply, resulting in withdrawal. These fish mope around the tank floor until they’re given antidepressants, at which point they begin happily swimming near the surface again.

It’s impossible to correlate fish depression with that of a human, but Pittman believes the symptoms in fish—losing interest in exploring and eating—makes them viable candidates for exploring neuroscience and perhaps drawing conclusions that will be beneficial in the land-dwelling population.

In the meantime, you can help ward off fish blues by keeping them busy—having obstacles to swim through and intriguing areas of a tank to explore. Just like humans, staying active and engaged can boost their mental health.

[h/t The New York Times]


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