SPEAKER_01 0:06

So the other day I came across this beautiful brown bird with black, brown, and gray feathers. It was small and stout and it chirped boldly, had bright white cheeks. Naturally, I looked it up and I told Sabrina about it.

SPEAKER_02 0:17

Yeah, it turns out they were sparrows. I was telling Heath how my dad despises them for nibbling on his tomatoes, but I think he's being dramatic.

SPEAKER_01 0:24

I'm just having a hard time imagining how these cute tiny birds could be so hated. They seem pretty unproblematic to me. Nessa, what do you think?

SPEAKER_03 0:32

I mean, honestly, I hadn't paid much mind to it before, but now I'm kind of curious, are sparrows the good or bad guy?

SPEAKER_02 0:44

Okay, let's start with the basics. How do you identify sparrows? I feel like they look like every other bird.

SPEAKER_01 0:49

Well, there are sparrows from all over the world, right? To simplify, there are old world sparrows, which originated from Afro-Eurasia, and New World Sparrows from the Americas. Today we're going to talk about old world sparrows.

SPEAKER_03 1:01

You've definitely interacted with them. They live in both rural and urban environments, wherever humans are. So street signs, city lights, near trash cans, building crevices. We'll come back to that.

SPEAKER_01 1:11

And that's probably part of why people have such strong opinions. Sparrows are so intertwined with human environments that we sometimes don't give them a second thought. But historically, people have gone to great lengths to try and get rid of them.

SPEAKER_02 1:23

One of the most dramatic cases happened in China during the late 1850s when sparrows were officially labeled enemies of the state. Well, isn't that a bit dramatic? Mao Zedong was a leader of communist China, but came from a farming background himself. He grew up in a peasant family in Hunan, so agriculture, poverty, and rural life weren't abstract ideas to him. By the late 1950s, Mao wanted to prove that China could rapidly transform itself.

SPEAKER_03 2:09

The belief was that if the whole population mobilized together, China could catch up with or even surpass the West.

SPEAKER_01 2:15

From this came the Four Pests Campaign, which identified four quote-unquote enemies who threatened public health: rats, flies, mosquitoes. Take a guess of the fourth one.

SPEAKER_03 2:25

Sparrows. The Chinese government believed that the sparrows were affecting the grain seed production from farms, reducing the country's food supply.

SPEAKER_01 2:32

This was based mostly on farmers observing sparrow flocks around grain fields. And it wasn't totally baseless. Sparrows do eat grain. But what the government missed was that sparrows were also eating the insects that destroyed crops. So they were only looking at half the picture.

SPEAKER_02 2:47

Scientists tried to point out consequences of losing these sparrows, that eradication could cause insect population spikes, but given it was China in 1958, speaking out against a national campaign wasn't just a professional risk, but also politically dangerous.

SPEAKER_01 3:02

Think about it.

SPEAKER_03 3:10

It got intense fast. This wasn't casual pest control. It was violent and systematic. People destroyed nests, they broke eggs, killed chicks, trapped birds, used poison bait, and attacked sparrows with poles, slingshots, and guns.

SPEAKER_02 3:25

People gathered outside, banging pots, drums, anything to create a loud continuous disturbance. And sparrows have to land periodically to conserve energy, so if you keep them from landing long enough, the birds would literally fall from the sky from exhaustion.

SPEAKER_03 3:40

There are horrifying photographs from this era showing masses of dead sparrows and huge crowds participating in the campaign, even children. And this was official policy.

SPEAKER_02 3:49

Schools, workplaces, and communities were mobilized to help eliminate sparrows through these violent manners.

SPEAKER_01 3:55

In their eyes, it was quite patriotic. Participation was framed as a civic duty, and efforts were encouraged through propaganda, like huge posters and public campaigns, and organized rallies, with the campaign slogan translating to Man Must Conquer Nature.

SPEAKER_02 4:09

Yeah, and by the numbers, it quote unquote worked. Somewhere between one and two billion sparrows were killed, bringing them near extinction.

SPEAKER_03 4:16

But just as scientists feared, once sparrow populations collapsed, insect populations boomed, especially locusts and other agricultural insects that were keeping sparrows in check.

SPEAKER_02 4:26

Areas with more aggressive sparrow killings saw rice production drop around 5% and wheat around 8%. Which sounds small until you remember this was across enormous agricultural regions already under pressure to feed hundreds of millions of people.

SPEAKER_01 4:39

So humans removed the pest, but accidentally removed the thing that had been protecting their crops the entire time.

SPEAKER_03 4:45

This contributed to the Great Chinese famine between 1959 and 1961, with around 30 million deaths. Some estimates tie the sparrow campaign alone to nearly two million deaths.

SPEAKER_02 4:57

Eventually, the Chinese government quietly removed sparrows from the enemy list altogether.

SPEAKER_01 5:02

The government viewed nature mechanically, removed the bad organisms to improve productivity. But ecosystems don't work that way.

SPEAKER_03 5:10

Predators control pests, pests affect crops, crops affect food systems. It's all connected.

SPEAKER_01 5:15

So the real tragedy isn't just the ecological disaster, it's that it reflects this deeply human belief that the state can dominate nature and that no one, not even scientists, can say otherwise.

SPEAKER_02 5:27

Okay, so we told you about China, but I feel like we should also tell you about the sparrows we're a bit more familiar with here in North America. This wasn't the first major conflict humans had with the sparrows either. Turns out people have been going back and forth with these birds for a long time.

SPEAKER_03 5:43

Let's rewind to 19th century America, because while China was on a mission to wipe sparrows out, Americans were intentionally bringing sparrows here from Europe.

SPEAKER_02 5:52

Quick clarification though. China's campaign targeted the Eurasian tree sparrow while the species introduced to the US was the house sparrow, a species also in the old world sparrow family.

SPEAKER_03 6:02

That distinction actually matters a lot because house sparrows were understood to be tougher, more aggressive, and basically built for city life. They nested in buildings, tolerated noise in crowds, and could raise multiple broods every single year. So once they settled somewhere, their populations could grow really fast.

SPEAKER_01 6:18

Eurasian tree sparrows were more associated with rural areas and farmland, but house sparrows, they were made for more dense human environments. So rooftops and gutters and vents and signs, basically any small opening in a structure.

SPEAKER_02 6:32

Which made them really appealing to European settlers who were trying to recreate a sense of the old world in the Americas. Most historians traced one of the first major introductions to a man named Nicholas Pike, who released eight pairs of house sparrows into Brooklyn in the 1850s after bringing them over from Liverpool. And there were a couple of reasons people wanted to bring them here in the first place.

SPEAKER_03 6:52

The first was nostalgia. To European settlers, the house sparrow was familiar, something they'd grown up hearing and seeing around villages and markets back home. There was actually a broader pattern of settlers intentionally importing European plants and animals because they believed it made American landscapes feel more civilized, more recognizable.

SPEAKER_01 7:10

This mindset ran pretty deep. There was even a group called the American Ecclematization Society that wanted to introduce every single bird mentioned in Shakespeare's play Here to North America. They were trying to bring Europe here.

SPEAKER_02 7:23

But House Sparrow fit right into that. It was a little piece of home.

SPEAKER_03 7:26

The second reason was more practical. As American cities were rapidly expanding, urbanization was disrupting local ecosystems in a big way. New buildings, cleared land, and dense human settlements created conditions that certain insects thrived in. Linden moth caterpillars, inchworms, and other insect pests were tearing through the vegetation.

SPEAKER_01 7:45

Basically, humans have built these environments and inadvertently created the conditions for an insect explosion. And since house sparrows were known to eat insects, people assumed they were a natural fix.

SPEAKER_02 7:56

And part of what made house sparrows so effective at exploiting these new urban environments comes down to something called neophobia.

SPEAKER_01 8:02

Which sounds like a medical condition.

SPEAKER_02 8:04

Right. It literally just means fear of new things.

SPEAKER_03 8:07

Scientists compared house sparrows to Eurasian tree sparrows and found something really important. House sparrows adapted to unfamiliar objects much faster.

SPEAKER_01 8:16

So basically, if humans suddenly changed an environment, like adding a new structure, introducing a new food source, or changing a city space.

SPEAKER_03 8:24

House sparrows were way more daring to explore it. Meanwhile, Eurasian tree sparrows stayed cautious for much longer.

SPEAKER_01 8:30

Researchers even found that house sparrows habituated to new objects within about a week while Eurasian tree sparrows still avoided them. And this matters because cities are constantly changing environments.

SPEAKER_03 8:40

Exactly. So being willing to explore unfamiliar things can mean more access to food, shelter, and nesting opportunities.

SPEAKER_01 8:46

Which helps explain why house sparrows seem so comfortable around humans.

SPEAKER_03 8:50

Yeah, they almost evolved alongside human expansion itself. And because they aren't afraid of novelty, they're able to exploit human-made environments really effectively.

SPEAKER_01 8:59

So their success essentially comes down to behavioral flexibility.

SPEAKER_03 9:02

For a while, communities actually welcomed them. People seemed to genuinely like having them around, but that changed pretty quickly once the population started exploding. Humans have a lot to do with it, which is why we've got to tell you about it.

SPEAKER_02 9:17

We needed the help of an expert to explain this, so we reached out to Dr. Andrea Liebel, an associate professor at the University of South Dakota, who studied house sparrows during her PhD.

SPEAKER_04 9:26

When I did my PhD, I worked a lot in house sparrows. I studied them in Kenya. That's one of the most recent introductions of house sparrows. They were introduced to Mombasa on the eastern coast of Kenya in the 1950s, and they spread all the way west and one of the westerns.

SPEAKER_01 9:43

That made Kenya a really unique research site. She could compare older established sparrow populations near the original introduction area with newer populations at the edge of the expansion. What stood out was where she found them.

SPEAKER_04 9:55

So when I was catching them, I was catching them in garbage dumps in Kenya. But then I would also get them in slums sometimes, which was an ideal. But places where there are garbage, there were some places where the ideal place was like a gas station, or there was this milk storage facility where people would bring their milk from their home cows and mix it all together and pasteurize it, or and then they would bottle it and send it out. I put a whole bunch of nest boxes there, and so they were always associated with humans. I think they need the structures.

SPEAKER_02 10:27

But the birds themselves also had biological advantages that made them unusually adaptive. How sparrows were evolutionarily set up to thrive around humans.

SPEAKER_03 10:35

Dr. Lebel's work also looked at what made sparrows at the edge of that expansion so successful, not just where they moved, but how their bodies responded to new environments.

SPEAKER_04 10:44

What happens with the sparrows at the range edge is they're able to raise it really high and then bring it down really quickly too.

SPEAKER_01 10:51

By eight, she's referring to corticosterone or quart, a stress hormone in birds.

SPEAKER_03 10:56

We spoke with Dr. Michelle Rentzel, an associate teaching professor and vice chair of undergraduate education in UCLA's Institute for Society and Genetics, who is a trained avian behavioral endocrinologist who spoke to us a little bit more about this.

SPEAKER_00 11:10

My research background is in hormones and behavior, which is the study of how hormones interact with behavior, but in non-humans. In particular, for my PhD work and my postdoctoral work, I looked at stress hormones and other steroid hormones and how they interact with various elements of behavior in a couple different species of birds. We like to think of the physiological stress response as a way that sort of the environment is communicating with the rest of the body and the body is able to respond. So it's kind of like a messenger. Cortisol is really a messenger between the internal and external world and the rest of the body. So in the context of, say, an anthropogenic disturbance, having a stress response might help an organism to increase its alertness and its awareness. So that's one of the impacts of elevated cortisol. It might actually impact the brain, right? And help kind of retain a memory or pay attention to what's happening. That might be really advantageous if you're facing some sort of new threat or novel environment or like a human being showing up in your territory or something like that.

SPEAKER_02 12:18

Dr. Lee will explain that this quick rise and fall helps sparrows cope with stressors without keeping their bodies in a constant state of stress.

SPEAKER_03 12:25

So they elevate court really quickly, they cope with the stressor that they need to deal with, and then they bring it back down.

SPEAKER_01 12:30

So most organisms, but especially for sparrows, stress isn't a weakness. And short bursts actually helps them respond to unpredictable environments.

SPEAKER_02 12:38

Basically, they can turn the stress response on when they need it, then shut it off before it becomes damaging.

SPEAKER_03 12:44

And that matters because human environments are full of unpredictable stressors: new foods, new nesting sites, new predators, traffic, buildings, people, noise.

SPEAKER_01 12:54

And this adaptability doesn't stop at stress. Researchers studying urban house sparrows discovered that many of them carry a gene called AMY2A, which helps them produce an enzyme called amylase. Amylase helps break down starches, things like wheat, corn, and potatoes, which are all major agricultural crops tied to human civilization.

SPEAKER_03 13:14

Researchers from Norway, Iran, and Kazakhstan sequenced sparrow genomes from across Eurasia and found that urban house sparrows split from wild sparrow populations around the same time farming developed in the Middle East roughly 11,000 years ago.

SPEAKER_02 13:26

So human agriculture likely shaped their evolution. They weren't just randomly invading human spaces. Humans kind of created the conditions that helped them succeed.

SPEAKER_01 13:35

As agriculture expanded, especially grain farming, humans created huge and predictable food sources that sparrows could rely on.

SPEAKER_02 13:42

And as cities grew around those agricultural systems, sparrows found even more places to nest, reproduce, and survive.

SPEAKER_03 13:49

So when we describe sparrows as quote-unquote urban birds, that urban environment didn't just appear naturally. Humans built it through agriculture, industrialization, transportation networks, and expanding cities.

SPEAKER_01 14:00

These urban environments only grew more well into the 20th century, especially after World War II. That World War World War II. These urban environments only grew more well into the 20th century, especially after World War II, when agriculture became more industrialized.

SPEAKER_02 14:20

By that point, farms got larger, more mechanized, and much more focused on efficiency and maximizing production, which also meant there was less tolerance for species that interfered with that system.

SPEAKER_01 14:31

So the centuries-long conflict with sparrows became tied not only to crop damage, but also to protecting a highly industrialized agricultural economy. Does that make sense?

SPEAKER_03 14:40

Yeah, and sparrows were living directly inside those systems the entire time.

SPEAKER_02 14:44

Let's also consider the sparrow's reproduction biology, which helped them spread successfully.

SPEAKER_03 14:49

Okay, so house sparrows are considered socially monogamous, meaning they usually form long-term pair bonds.

SPEAKER_01 14:55

Aww, cute.

SPEAKER_03 14:56

Well, socially monogamous. Genetically, things are more complicated. These birds are messy.

SPEAKER_01 15:02

Researchers found that female house sparrows sometimes may outside these long-term pair bonds. This is called extra pepperinity.

SPEAKER_02 15:09

And one reason this is important is because it increases genetic diversity among offspring, which can improve survival in changing or stressful environments.

SPEAKER_03 15:16

Exactly. Greater genetic diversity means a population has a better chance of adapting to disease, environmental stress, climate differences, or food shortages.

SPEAKER_01 15:24

So their biology keeps reinforcing the same pattern, flexibility.

SPEAKER_02 15:29

And that flexibility also shows up in the way sparrows reproduce across different climates.

SPEAKER_03 15:33

In colder regions near the poles, house sparrows rely heavily on changes in daylight and temperature to determine when to breed.

SPEAKER_01 15:40

This makes sense because they need their chicks to hatch when food availability is highest.

SPEAKER_02 15:44

But near the equator, daylight and temperature stay relatively stable year-round, so sparrows adapt differently.

SPEAKER_01 15:50

In places like Panama, India, and parts of Africa, researchers found that sparrows oftentimes breed around rainfall patterns instead.

SPEAKER_03 15:57

And some populations even breed during completely different seasonal conditions depending on the local environment.

SPEAKER_02 16:02

So they aren't locked in on one specific reproductive strategy. They're biologically flexible across radically different climates and ecosystems.

SPEAKER_03 16:10

So whether they're living in freezing northern regions or tropical urban centers, they somehow keep finding ways to survive and reproduce.

SPEAKER_02 16:17

With that in mind, we gotta tell you why the sparrow population boom was so significant.

SPEAKER_01 16:24

In our research, we learned that part of the reason why sparrows were so problematic was because of the actions that they took against non-native birds. Recall that we briefly mentioned that house sparrows are old world sparrows, meaning that they didn't originate from North American land.

SPEAKER_02 16:38

This is significant because when house sparrows came onto American soil, they needed a place to set up their nests.

SPEAKER_03 16:44

Many of the urban areas that they gravitated towards were already occupied by birds who already claimed these spaces fair and square. Some examples you can think of are purple martens, eastern bluebirds, and tree swallows.

SPEAKER_01 16:55

So sparrows are actually quite aggressive as they go through great lengths to try and take over the nests. And when scientists say competition, they don't just mean birds arguing over space.

SPEAKER_02 17:05

We're talking about animals actively fighting for territory and survival.

SPEAKER_03 17:09

There's actually research from scientists connected to the Cornell Lab of Ornithology showing just how intense this competition became. According to their findings, house sparrows were responsible for nearly half of all reported nest box competition involving invasive bird species.

SPEAKER_04 17:31

I've seen them go into other nests and actually kick eggs and babies out. So I think that's probably the the biggest concern is it's the effect of that species on other species.

SPEAKER_01 17:44

So we can see how these are no longer just tiny, harmless chirping birds. They're skilled and strategic in their abilities to dominate other species.

SPEAKER_03 17:52

Yeah, like how male house sparrows defended nesting territory extremely early in the season, often before migratory birds like bluebirds and swallows even arrived.

SPEAKER_01 18:00

So by the time native birds came back to breed, many nesting spaces were already occupied. And once the sparrows settled into their new homes.

SPEAKER_02 18:08

Baby, it became theirs. But what's just as interesting is that sparrows didn't just disrupt bird populations.

SPEAKER_03 18:13

As house sparrow populations exploded, people also started complaining about the effects they were having on human spaces.

SPEAKER_01 18:19

The sparrow became the ultimate safety hazard. They gathered around rooftops, barns, city buildings, and their cacophonous sounds were at worst mildly annoying, the research tells us.

SPEAKER_02 18:30

The problem wasn't just the noise, though. It was their droppings and feathers that were causing great gernatorial problems with clogged gutters and vents, especially if they were near major roosting sites.

SPEAKER_01 18:40

There are publications out there emphasizing that the leave behinds for fire hazards.

SPEAKER_03 18:44

So Americans were increasingly seeing how sparrows as aggressive towards other birds and disruptive in human spaces. But nowhere did that hostility towards sparrows become more important than in the agricultural space. Here's one thing Dr. Liebel had to say.

SPEAKER_04 18:58

In kind of agricultural areas, they actually are a really big problem because they'll go into the agricultural areas around chickens, let's say, and they'll pick up diseases. And for a lot of diseases, they can be carriers. And so we've seen that with bird flu that house sparrows can be carriers, and so they'll pick up, they'll like go amongst the chickens in the poultry areas, they'll pick up these diseases, and then they leave and they bring those diseases out with them.

SPEAKER_01 19:24

So this makes the push label more complicated. In agriculture, sparrows are not just symbolic invaders or annoying birds out of feeder. The movement between poultry areas and their wider environment can create real disease concerns.

SPEAKER_02 19:36

But that's not all. Another pattern became very clear. The more house sparrows, the more crop damage.

SPEAKER_01 19:42

For example, I was reading into the study about greenhouse sparming systems that showed that higher sparrow densities are linked to higher damages to red pepper crops.

SPEAKER_03 19:50

This made it clear that a sparrow's diet wasn't limited to just insects. They munched on pretty much anything, especially seeds.

SPEAKER_02 19:56

Sparrows are opportunistic feeders and they're willing to hang around in parking lots, parks, or cafes waiting for crumbs.

SPEAKER_03 20:02

So just imagine the freedom they'd have when they encounter entire fields of food. Just because they're social doesn't mean that they don't find their way onto the fields away from people.

SPEAKER_01 20:11

Researchers found that house sparrows are willing to travel surprisingly long distances to reach dependable food sources.

SPEAKER_02 20:17

So these birds have a field day, literally, when they come to these agricultural spaces filled with grains, seeds, peppers, etc. It's a free-for-all.

SPEAKER_03 20:25

So with sparrows raiding crops, spreading disease, and taking over nesting spots, it was only a matter of time before humans decided enough was enough.

SPEAKER_01 20:34

As sparrow populations kept growing, public opinion shifted. They were no longer framed as helpers, they became invaders.

SPEAKER_02 20:40

It's interesting that the shift wasn't only happening in casual conversations or newspaper complaints. It eventually became part of a much bigger political language about invasive species.

SPEAKER_03 20:50

Historian Peter Coates shows that anti-sparrow rhetoric in 19th century America borrowed heavily from anti-immigrant discourse. Sparrows were called foreign invaders, accused of stealing resources, displacing native species, overcrowding cities.

SPEAKER_01 21:02

Which mirrored exactly how immigrant groups were being talked about politically at that same time. And scholar Bonnie Suburmanium actually explains the mechanism for why that overlap wasn't a coincidence.

SPEAKER_02 21:13

She points out that the language used to describe invasive species follows the exact same progression used to describe immigrants. A species enters a country as an alien or exotic, over time it becomes a resident, eventually it gets naturalized.

SPEAKER_01 21:26

And the parallels go deeper than terminology. Publications about sparrows describe them as foreign invaders overtaking native birds' homes, reproducing rapidly, stealing agricultural resources. Those same characterizations, being aggressive, prolific, and economically destructive, were being applied to immigrant populations in newspapers and scholarly journals at that same time.

SPEAKER_03 21:46

Sabramium argues that this wasn't a coincidence. Scientific language demonizing sparrows and political language villainizing immigrants were being constructed at the same time, each giving the other legitimacy.

SPEAKER_01 21:57

And that language shouldn't just stay in the 19th century. In 1999, it was written into federal law.

SPEAKER_02 22:02

Clinton's executive order on invasive species directed the federal government to, and this is the real language from the order, fight the invaders and defend the nation against aggressive predators and pests. Concerns about invasive species became a way to reassert control and sovereignty over nature, but also over who and what belongs.

SPEAKER_01 22:32

The order even folds invasive species into the language of national security, warning they could threaten agriculture, infrastructure, and public health.

SPEAKER_03 22:41

So the rhetoric evolved, but the underlying logic stayed the same. Something foreign arrives, it doesn't belong, therefore it needs to be controlled.

unknown 22:48

Dr.

SPEAKER_01 22:48

Renzel actually had more insights about this.

SPEAKER_00 22:52

So even this idea of invasive species is problematic, and there's lots of geopolitical implications of using that term, right? We've saw this during COVID when we were talking about, you know, COVID itself, and it brought up all these sort of racist undertones. So we have to be really careful also, if we're thinking conservation, about how we're framing sort of the causes and the consequences and this whole idea of what is a native species and what is an invasive or an introduced species. And the reality is we've created a world where species move everywhere. And so how are we going to cope and kind of work to achieve some sort of balance with all those organisms and ourselves?

SPEAKER_02 23:34

So the sparrow became more than just a bird. It became a screen onto which people projected anxieties about who belonged and who didn't.

SPEAKER_03 23:40

And once sparrows were framed as outsiders threatening the nation, it became much easier for governments and communities to justify violence towards them and removing legal protections for them, allowing their nests and eggs to be destroyed.

SPEAKER_01 23:52

And at that point, the whole idea of sparrows as pests becomes more complicated. People weren't just reacting to the birds anymore, they were reacting to what the birds represented.

SPEAKER_00 24:01

It's not the house sparrow's fault that they're here. And it's really easy to demonize a particular species and to make claims and judgments that aren't really accurate to the reality of the world that we've constructed.

SPEAKER_01 24:17

So I know we just discussed the annoyance many have with sparrows, but I think it's also important for us to consider if they have any potential uses to humans in any way.

SPEAKER_02 24:26

Because one thing that surprised me in our research is that house sparrows are not only animals people try to control, they're also incredibly useful to science.

SPEAKER_03 24:33

Right. And one of the strongest examples is their role in studying evolution. House sparrows are one of the most widespread vertebrates in the world, and because they've been introduced across so many continents, scientists can study and compare how the same species adapts to totally different environments.

SPEAKER_01 24:47

House sparrows introduced to North America evolves noticeable physical differences across populations in roughly a century for evolution that's extremely fast.

SPEAKER_02 24:55

So instead of just seeing them as this invasive bird that spreads everywhere, scientists can turn that into evidence.

SPEAKER_03 25:01

Exactly. Their success becomes a research opportunity.

SPEAKER_02 25:04

There is a paper that explains that introduced species usually face genetic bottlenecks, meaning only a small number of individuals start a new population. That should make adaptation harder because there's less genetic diversity.

SPEAKER_01 25:16

But as we know, house sparrows often overcome that and still adapt rapidly to new spaces.

SPEAKER_02 25:21

Which is why they're so valuable. They help scientists study how animals respond to environmental change in real time and understand adaptation, invasion, climate responses, and survival.

SPEAKER_03 25:30

Now, if we switch to specifically looking at sparrow eggs, there's evidence that they can actually be an efficient alternative for experimenting with bird eggs.

SPEAKER_01 25:37

Yeah, this part was honestly unexpected. Researchers collected more than 1200 house sparrow eggs over three years from a colony of about 24 breeding pairs by putting nest boxes in livestock barns.

SPEAKER_03 25:48

And they found that house sparrow eggs can be utilized in nest predation experiments because the eggs are similar in size and shell thickness to many native forest songbirds.

SPEAKER_02 25:56

Yeah, and that makes them more realistic than alternatives like quail eggs, which are often too large and thick-shelled, or zebra finch eggs, which can be too small and fragile.

SPEAKER_03 26:04

So house sparrow eggs help scientists study what happens to other birds' nests, which is important because artificial nest experiments are used to understand predation risk, conservation problems, and why some bird populations may be struggling.

SPEAKER_01 26:16

So if the egg used in the experiment is unrealistic, the results can be misleading.

SPEAKER_02 26:21

Exactly. And then there's a third example, lead detection.

SPEAKER_03 26:24

Yeah, this one is fascinating. A recent article reported on research showing that house sparrows can help monitor lead exposure in children, especially in mining towns.

SPEAKER_01 26:32

Researchers collected blood samples from hundreds of sparrows at more than 40 sites, then compared those results to thousands of children's blood records from 1991 to 2022.

SPEAKER_02 26:43

And the results were shocking. Where sparrows had high lead levels, children nearby did too.

SPEAKER_03 26:48

And when you think about it, the logic makes sense. How sparrows live extremely close to people. They nest under leaves, forage in yards, and spend their lives in the same dust and soil children might be exposed to.

SPEAKER_01 26:58

So they're not just near humans, they're sharing our environments at a very intimate scale.

SPEAKER_02 27:02

And that completely changes how we see them because sparrows are not just birds living off human environments. They're helping reveal what those environments are doing to us.

SPEAKER_03 27:12

So all this to say, calling sparrows just a pest leaves out a huge part of its value. Because once we label a species as disposable, we may stop noticing the ways it is actually helping us understand the world we built.

SPEAKER_01 27:26

Once we started looking into all of this, the sparrow stopped feeling like just the bird people either liked or disliked.

SPEAKER_02 27:32

Yeah, because throughout history, humans continued creating relationships with sparrows. And then reacting to the consequences of those relationships.

SPEAKER_01 27:39

In China, sparrows were killed because they were believed to threaten food production.

SPEAKER_02 27:43

But in the United States, humans intentionally imported sparrows because they thought they would protect agriculture.

SPEAKER_03 27:48

Then later, those same birds became labeled invasive and destructive.

SPEAKER_01 27:52

Meanwhile, humans kept expanding the exact kinds of environments sparrows thrive in: cities, transportation systems, agriculture, food waste, and how sparrows adapted extremely well to these environments.

SPEAKER_03 28:04

So well that people eventually started trying to control their populations through trapping, nest removal, and exclusion methods.

SPEAKER_01 28:09

What's super interesting that we haven't mentioned is that sparrows are actually now declining in some urban areas too.

SPEAKER_02 28:14

Researchers point to things like pollution, pesticides, air quality, habitat change, and declining insect populations.

SPEAKER_03 28:20

So over time, sparrows have been viewed as useful birds, agricultural threats, invasive species, research subjects, and environmental indicators.

SPEAKER_01 28:28

And through all of it, humans were constantly reshaping the environments around them.

SPEAKER_02 28:32

The cities we built, the species we introduced, the ecosystems we changed.

SPEAKER_01 28:36

By the end of all of this, the sparrow starts to feel less like a simple good or bad animal.

SPEAKER_03 28:41

And more like a reflection of the environments and systems humans created around it.

SPEAKER_01 28:50

As we wrap today's episode, we'd like to extend our sincere thanks to Dr. Michelle Rensel and Dr. Andrea Liebel for taking time to sit down with us and share their expertise.

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Their insights helped us better understand not only the biology and behavior of the house sparrows, but also the broader ecological and evolutionary questions surrounding how animals adapt to changing environments.

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And thank you to everyone for listening. We hope this episode has given you a new perspective on one of the world's most familiar and surprisingly complex birds.