Previous: Nurseryfish Dads Give Their Young a Headstart… Literally
Next: Thank Goodness for Bacterial Cannibalism



View count:222,693
Last sync:2022-11-23 10:00
When humans build a city, most species in the area tend to disappear. But there are some, called synurbic species, that are living their best lives in our concrete jungles.

Hosted by: Stefan Chin

SciShow has a spinoff podcast! It's called SciShow Tangents. Check it out at
Support SciShow by becoming a patron on Patreon:
Huge thanks go to the following Patreon supporters for helping us keep SciShow free for everyone forever:

Kevin Bealer, Jacob, Katie Marie Magnone, D.A. Noe, Charles Southerland, Eric Jensen, Christopher R Boucher, Alex Hackman, Matt Curls, Adam Brainard, Jeffrey McKishen, Scott Satovsky Jr, James Knight, Sam Buck, Chris Peters, Kevin Carpentier, Patrick D. Ashmore, Piya Shedden, Sam Lutfi, Charles George, Christoph Schwanke, Greg
Looking for SciShow elsewhere on the internet?
Peregrine falcons


Northern water snakes

Flying foxes

Mugger crocodiles


Image Credits:,p%27-dichlorodiphenyltrichloroethane.svg
[♪ INTRO].

Cities are full of wonderful, exciting things, like museums, and nightclubs, and... raccoons that eat garbage! Yes, animals love our cities, too.

Some of them, anyway. When humans develop an area, most species tend to disappear. But there are some that not only survive in our urban jungles, they thrive there.

We call these animals "synurbic". And they're great examples of just how resourceful and adaptable creatures can be. Peregrine falcons used to be happy on their lonely cliffs.

And then humans discovered a wonder-chemical called dichlorodiphenyltrichloroethane—but let's just call it DDT because no one should ever have to say “dichlorodiphenyltrichloroethane.” It was such an effective pesticide that we used it everywhere — to control crop-eating pests, mosquitoes, bed bugs... During World War II, the military even used it on body lice! Unfortunately, it harmed off-target species, too.

While DDT isn't lethal to adult falcons, it weakens the eggshells they produce. So DDT-exposed falcons ended up making eggs that were all too easily crushed. By the mid 1960s, peregrines were dangerously close to extinction.

Thankfully, a breeding program established in 1970 helped bring them back. And that's where the story gets kind of weird. When captive-bred falcons were released back into the wilds of New England, a good number of them moved to New York City, of all places.

And in the midwestern US, apparently no self-respecting peregrine wants to be caught dead on an uncultured cliff-top. So now, almost all peregrines in that region live in urban areas. Which might seem kind of odd, but all you really have to do is ask yourself why anyone wants to live in the city.

And the answer is obviously the food. Cities like New York are renowned for their pizza, pastrami ... the pigeons ... well, maybe not so much for humans, but the falcons are definitely into the pigeon. Pigeons another synurbic species, so there are tons of them, and they're easy to prey on.

In fact, city falcons have it so good that they lay more eggs. In the wild, a peregrine clutch usually has three eggs in it. But in the city, a clutch can have as many as five.

Plus, the skyline of a big city isn't all that different from the cliffs they used to call home. Skyscrapers provide high nesting sites near steep drop-offs, where the birds can continue to catch prey the way they always have: by diving on it at incredible speeds. So the falcons probably feel right at home.

Now, raccoons also love cities for the food—the food we throw away, that is, hence the nickname “trash pandas”. Though, they aren't mindless scavengers. They've got real street smarts, and that's a big part of why they've taken so well to urban environments.

Some experiments suggest they're as good at solving problems as crows. And not only that, they're also capable of understanding cause and effect. And that makes sense when you look at their brains.

Raccoons have as many neurons as dogs, but their brains are much smaller, which means that the density of neurons is more similar to primates. Of course, the idea that raccoons are super smart probably isn't a revelation to anyone who has woken up to the sight of a week's worth of trash strewn across the lawn. Oh look, the raccoons have figured out how to bust into a “raccoon-proof” garbage can.

Again. And the more they're exposed to human inventions, the smarter they seem to be getting. Still, you'd think that a creature this clever could find food anywhere, so it might seem odd that they'd choose to live where there are tons of really dangerous animals—humans, I mean.

And the first urban raccoons probably didn't make that choice. As cities grew, they took over the raccoon's natural range. Once that happened, though, the raccoons went, “Cool, garbage.” And that was that.

Nowadays, our cities offer up so much food that the animals can eat and reproduce to their heart's content. For instance, in one park in Fort Lauderdale, Florida, researchers counted roughly 238 raccoons per square kilometer. Which is, like, a ton of raccoons—and that's way more dense than wild populations.

Now, the northern water snake is a fairly harmless species that looks a little bit like the very venomous northern cottonmouth. Which is pretty unfortunate for them, since some people kill cottonmouths on sight. Even worse, many humans that can tell the difference still don't like these snakes... because they're biters.

Oh, yeah, and they spray poop when they're disturbed. Which as you can imagine, makes them kind of hard to appreciate. Still, our antagonism hasn't stopped the snakes from moving into big cities.

Like raccoons, the snakes probably took to urban areas because they had to. We like our cities to be near waterways, and that's where these snakes live. But now that they're used to city life, they seem to prefer it.

Research suggests that when water snakes have access to both natural and urban areas, they choose the urban one. That could have something to do with an abundance of hiding places. They're often found hiding in stuff that we make, like piles of concrete and scrap metal, or the material we put on riverbanks to prevent erosion.

And having lots of places to hide is great for the snakes' survival, even when there are snake-hating humans around, because most humans know better than to go sticking their hands in a pile of rubble. And there may also be a thermal benefit to living in cities. Like other reptiles, they can't stay warm enough on body heat alone, so they prefer warmer bodies of water.

And urban rivers tend to be warmer than rivers flowing through natural areas. These snakes don't even need natural habitats. Pretty much any fresh water does the trick.

And we should be pretty excited about that. In one urban canal in southern Florida, researchers found that water snakes perform an important service: eating invasive fish. In fact, invasive gobies make up more than 90 percent of the diet of one northern water snake subspecies.

So this snake's presence is often a win-win—good for the snakes and for the surrounding habitat. But, urbanization is bad news for most bats. Most species—especially the smaller, slower ones—need darkness to remain safe from high-flying predators like owls.

And cities are full of light. But flying foxes don't seem to mind. And unlike raccoons and northern water snakes, who were sort of forced to live with people at first, scientists think these fruit-eaters may have moved into cities by choice.

That's because people like fruit just as much as the bats do. So, they plant fruit trees in their backyards. And these trees provide the bats with an abundant source of food.

Flying foxes might also feel more comfortable in cities because of their warmth. It's a phenomena known as the “urban heat island effect”. Basically, our artificial structures don't reflect as much heat during the day, and retain it well at night, so the whole area is a bit warmer than nearby wildernesses.

And warmer nighttime temperatures give the bats a nice, even climate for flapping around, stealing fruit, and pooping on peoples' stuff. Which has become somewhat of a source of conflict. You see, flying foxes are pretty big.

Adult grey-headed flying foxes, for instance, have a wingspan of around one meter. Which means that when they poop, they poop big. Plus, they're noisy, and kind of smelly.

So, people living in cities haven't been all that welcoming. In places like Australia, they've taken to putting nets or barbed wire around their fruit trees to discourage snacking —which, sadly, can kill the bats. And, for a bat, there are other perils to city life—like, the heightened odds of flying into a power line.

But still, the free meals do seem to be offsetting the hostile neighbors, as their numbers seem to keep growing. Mugger crocodiles are a medium sized species of crocodile that lives in India. And they were once really abundant, but then people became fond of crocodile skin bags and belts.

Luckily, in 1972, they became a protected species, and now, they're on the rebound. One of the areas where they're coming back is the Vishwamitri River in Vadodara, India. Around 250 crocs live in this urban waterway.

And at first, humans in the area tolerated them because they have religious significance. But... humans and crocodiles don't really get along. And that's made the city a pretty dangerous place for both the people and the crocs.

Also, muggers are migratory, so they're often killed by cars while attempting to cross roads. And if that's not reason enough to leave, the river they live in is extremely polluted. Basically all of Vadodara's sewage is dumped directly into it.

But, when officials have tried relocating the animals, they tend to come back. And, weird as it might seem, that's probably because of all that sewage. Polluted rivers don't tend to have a ton of fish, but the crocs can improvise and snag animals like dogs and goats that wander near the water.

And when that meat's hard to come by, they just feed on refuse. See, crocodiles are hunters, but they're also scavengers. And in an urban environment, they do a little bit of both.

Researchers even think some of them would rather scavenge than hunt, because hunting is more work. But this life of leisure isn't necessarily good for them. A few of them even appear to be overweight.

But, if things were too bad, there would be a lot fewer of them. And some experts think that their presence has been good for the river, too, because they help clean up some of the waste before it decomposes. Macaques haven't always lived in cities.

Their first interactions with humans probably occurred in temples, where they were welcomed because of their religious significance. Then, cities were built near and around the temples. And as it turned out, city life agreed with them.

Macaques are actually a lot like us, which is to say that they're super adaptable. They can thrive in all sorts of habitats—like, tropical jungles, temperate forests, deserts, and swamps. So it probably wasn't that hard for them to ease into city life.

And, unlike most of the other animals on this list, the humans in those cities have been pretty chill with it. Sure, they can be a bit of a nuisance, what with all the begging for handouts and stealing from anyone who isn't paying attention. But they're good for the economy.

Tourists love urban macaques, and tourists spend money, so there's a whole industry that's grown up around interacting with city monkeys. It's also pretty obvious why the monkeys do so well. Foraging for food in the forest is much harder than getting it handed to you just for being cute.

One temple even has an annual festival which includes a feast ... for the monkeys. In fact, the monkeys have become so dependent on humans for food that when COVID-19 shut down the city of Lopburi in Thailand, the local macaques made the news for brawling over a pot of yogurt. But aside from the usual abundance of food, there are other perks for the monkeys, too—like, that the temples provide safe, protected housing.

Macaques have been hanging out in cities for so long that they're almost domesticated — almost. While they're comfortable around people, they're nobody's pet. They still live in troops and can be really aggressive—especially when a person doesn't have or chooses not to give them what they want.

Still, we kind of like having them around, and they aren't going to leave of their own volition. So we'll probably have city monkeys for a long time to come. When humans built the first cities, they probably thought they were shutting out the rest of the world.

But we're just one clever animal in a world full of clever animals. So it was almost inevitable that some of them would come join us in our safe, warm, and abundant urban habitats. Thank you for watching this episode of SciShow!

And thank you to all of you who support the show on Patreon. We're only able to keep making fun, free, educational YouTube content because we have this wonderful community of patrons. So thank you to all of you who are a part of that community and help us keep making this content.

If you want to learn more about joining our patron community, you can go to [♪ OUTRO].