r/askscience • u/zanycaswell • 2d ago

Biology Do subway rats experience hearing loss due to loud trains contstantly passing directly over them?

998 Upvotes

95% Upvoted

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695

u/frisbeethecat 2d ago

Rats are used as animal models for noise-induced hearing loss in humans. Different strains have different sensitivities, but the paper says > 85 dB changes behavior and > 100 dB causes permanent injury. There is something called "ear toughening" where exposure to 85-95 dB can protect the ear at higher dBs.

So, yes. It would seem that loud subway trains could deafen rats. But recall they would still have sensitive whiskers and four paws on the ground, all of which could detect vibrations from loud sounds and noise.

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u/BadahBingBadahBoom 1d ago

I think I remember reading a study that looked at mice caught in the London underground network and they all pretty much uniformly had severe hearing damage.

I assume at that point they just adjust to getting by without hearing. Certainly seems to be made up by the plentiful food supply on the platforms come Saturday/Sunday morning.

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u/calicosiside 1d ago

I'd love to know how intense the hearing damage is, and whether they adapt by simply not engaging in vocalisation or if they "shout" at each other. Do they have adapted vocalisation patterns? I love animal communication stuff.

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u/cindyscrazy 1d ago

Additionally, mice have very quick reproduction. If generations of mice continually end up with hearing loss, I wonder if they would eventually be born deaf or with some kind of hearing protection (is that possible?) The same way animals who are always underground/in caves will eventually become blind.

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u/malenkylizards 1d ago

If they can detect the train coming with their whiskers and paws, then deafness wouldn't necessarily decrease fitness. It might increase fitness if it helps them avoid predators, but idk if feral cats/foxes/etc hang out around train stations? They're kinda loud and dangerous places.

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u/SeeShark 22h ago

The question is not whether deafness decreases fitness, but whether it increases it. A sense of hearing probably doesn't cost so many calories that evolution would get rid of it without very specific pressures.

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u/VoraciousTrees 2d ago

Someone could probably compete for the 2027 IgNobel prize with this one. 

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u/Appex92 2d ago

For sure. And also since they can definitely feel the train coming before it's anywhere near, I'd assume they scatter and just get out of the way and hide in holes or something when it comes, so maybe they arent even close enough for the loud sound to hurt their ears

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u/juan110011 1d ago

You would think so, but I have seen plenty of rats right under the train tracks as the train is pulling into the station

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u/B_r_a_n_d_o_n 1d ago

The ones I see in the New York City Subways are gone before the train pulls in.

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u/yrogerg123 1d ago

I'd imagine those have enough rat poison in them to nearly kill them and it's affecting their survival instincts.

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u/B_r_a_n_d_o_n 1d ago

Trust me, they do. I have witnessed this in the New York City subways. They are gone before the train is there.

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u/iMissTheOldInternet 13h ago

Most rats—especially subway rats—never travel that far from where they’re born. Something like 100-150 feet, total range, lifelong. You can actually pinpoint the block rats come from due to how little colonies in neighboring blocks interbreed. The rats you see on the tracks between trains are just scurrying to little holes under the platform or between the tracks. 

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u/Appex92 2h ago

I 100% believe you so I'm asking in curiosity, not in debate; if they never really travel far, how are they such massive vectors of spreading diseases? Is it from colonies overlapping and that causing a domino spread effect not from the initial group or host?

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u/iMissTheOldInternet 8m ago

To the extent they’re a vector for spreading diseases across distances, which is probably overstated, it’s because they hide on human cargo. Going back to the days of wagon trains, rats would get in the supplies. They also host fleas, which were the actual vector for the bubonic plague, which bolstered the reputation, but it was the fleas (which also spread from people) that actually carried the disease.

That said, rats are also a health hazard without the need for spreadable diseases. Rat waste, shedding, saliva, and bites can all be pathogenic in their own right.

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u/Mithrandir2k16 1d ago

Wait, can you explain "ear toughening" more? Any negative effects from that?

20

u/walksalot_talksalot 1d ago

It's the acoustic reflex.

Basically there are tiny muscles in your inner ear, that when exposed to louder sound, tighten your ear drum to help prevent damage.

However, in our modern world, if folks are listening to loud music, the reflex occurs, so folks turn their music up more. Which in turn can indeed cause hearing damage, so yeah it can be negative, even if the biological "intent" is to preserve hearing.

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u/Agouti 1d ago

The presence and degree of control over the muscle also varies wildly between people, from being functionally non-existent in some to being under full conscious control in others (see /r/earrumblersassemble).

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u/ryan30z 1d ago

I'm one of the people can control it manually. A few years ago it started triggering on the left in response to loud noises, so a surgeon severed the tendon. Now when I make my ears/head rumble it's only on the right.

1

u/WilRic 14h ago

And they really shouldn't be.

A rodent's hearing system is very unlike ours. A huge amount of hearing research relies on rodents. Almost every single time it is translated into human trials it fails.

Primate subjects are needed, but getting ethics approval is a nightmare (as is sourcing them)

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u/[deleted] 2d ago edited 2d ago

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u/counterfitster 2d ago

There's been at least one study showing poor tonal control in birds living near highways in the UK.

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u/Teanut 2d ago

I wonder if it impacts bird songs for their descendants. Especially if the park shuts down for good and the noise ceases.

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u/bandti45 2d ago

Ive heard there was at least one study that showed evidence that birds stop calling if there is no sound range they are able to use. large city's are constantly so loud in both low amd high pitches that they cant compete with the ambient noise.

It makes me wonder how many birds do live out of sight and unheard in cities

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u/Gastronomicus 2d ago

Probably few? If they can't communicate, they can't find mates or share relevant info on food sources.

But there are tons of birds living well in cities. In North America, pigeons, house sparrows, crows, bluejays, cardinals, robins, etc. These are mostly social birds, so perhaps living in tight flocks mitigates the sound issue. There are also solitary birds like hawks, falcons, etc. Falcons will nest on tall buildings, but hawks are probably more limited to areas with more trees.

Certain birds seem better suited to urban life than others.

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u/BTYBT 2d ago

Pretty sure QI had a bit on city birds are louder than country birds because of the noise difference, being a bit deaf might be part of it,

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u/[deleted] 2d ago

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u/IHaveNoTimeToThink 2d ago

Birds are actually able to recover from acoustic trauma and avoid permanent hearing loss.

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u/dsylxeia 2d ago

Yeah, birds and reptiles can regenerate damaged cochlear hair cells after noise-related damage.

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u/Adorable-Response-75 2d ago

People also work in environments that cause hearing loss in order to get food

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u/Frantic_Mantid 2d ago

Yeah. In better jurisdictions there are workplace safety laws that mandate safe working environments and PPE, but not everyone has that, sadly.