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Bats slam into buildings because they can't 'see' them (nature.com)
67 points by TrickyRick 14 days ago | hide | past | web | 37 comments | favorite

This reminded me of (humor) http://www.mjt.org/exhibits/foundation_collections/depmori/d...

"The key idea in the Griffith hypothesis was that as the Myotis lucifugus emission increased in frequency, the emission actually crossed the thresholds from the extreme ultraviolet into the X-ray, thereby allowing the bat to fly unharmed through solid objects."

Reminds me of a an anecdote about the F-117 Nighthawk which was the first stealth airplane nearly invisible to radar. Apparently the engineers working on it would come into the airplane hangers to find many dead bats as it was also invisible to sonar.

Interestingly enough this made the engineers realize the stealth technology also could work for submarines which led to the IX-529 Sea Shadow stealth ship.

The bats died because the radar absorbent material used on the F-117A was highly toxic.

Poor bats. They also get their lungs exploded by the pressure differences created near wind turbines: https://www.wind-watch.org/news/2016/09/27/wind-turbines-are...

Meh, a 5 Mega Watt wind turbine kills less wildlife than the average outdoor cat.

turbines and cats put different selective pressure on the prey population - cats kill weak, ill, etc. thus improving the overall quality of the population where is turbine kills are probably spread uniformly and even may be skewed toward healthy active animals.

Something to keep in mind is that turbines don't actually kill a statistically significant number of bats or birds. While unfortunate, it's highly unlikely to stress the populations of any particular species.

Modernity comes at a cost.

How did you come to this conclusion? This is so unbelievable wrong I don't even know where to begin.

Cats do not just kill weak animals. They kill strong and healthy animals at an alarming rate. Cats have been responsible for at least 33 island animal extinctions in recent/recorded times [0].

[0] https://www.nature.com/articles/ncomms2380

There are 10B birds born per year in the US. In Nature pretty much everything is a food for the next level in the food chain, and there is no family&friends funerals. The more weak/ill/old - the higher probability to become predator's dinner. We don't have dead old birds littering the streets of cities. Somebody takes care about it.

And as you see from your own link cats mostly eat smalls mammals. Around humans it is mice and rats mostly. Rats do enjoy bird eggs and there is no protection here, until of course somebody takes care about the rats, like for example cats do.

As result cats do positive service to the birds population. The population which somehow manages to survive the urban and agricultural development - the main dangers for the wildlife causing population decimation and extinctions.

And island extinctions, really? So the cats brought by humans should have just committed suicide by starving themselves? Of course things can easily go wrong in any small system when the system gets severe kick from outside. And humans do just that to various eco-systems. How many species on various islands got extinct once humans reached those islands?

That's an overly simplified model to the point of incorrectness. A Lion wants a sick / old / or young water buffalo because it's less dangerous. However, a house cat does not really care about a mouse or bird.

If you look at mice reproduction they mostly get eaten before adulthood. Young healthy animals are often preferred prey because they are easy targets.

Finally, predators regularly drive species to extinction, which is a large part of why the vast majority of species to ever exist are not currently around.

TLDR; Cat's need 8 adult mice a day if that's all they are eating and they really can't afford to just look for sick animals. They easily hunt healthy adult birds, some baby rabbits, or other small animals.

Where do you think tens of billions of old mice/rats that are to die yearly are supposed to go, especially in developed areas where there are not many other predators?

In predation even without any specific choice by the predator, the resulting prey is naturally skewed toward weak/sick/old, ie the ones who is slower, has lower attention/senses, etc. Until some age the young are naturally on the weakest side and not surprisingly may fell prey a lot. Such filtration results in more healthy/agile/stronger adult population.

Relative size makes a big difference. The most extreme version of this is krill, as a blue whale really does not care about the fitness of the millions it needs to eat.

What your missing is most mice don't reproduce. The average litter is 6-8 and mice can have multiple litters per year. So, mice basically never reach old age.

The selective pressure has more to do with caution because a completely heathy mouse can't out run a cat / owl etc.

Put another way cats rub at up to 48 Km/h mice 13 Km/h. Thus, 'fitness' has little to do with athletic prowess.

> "Meh, a 5 Mega Watt wind turbine kills less wildlife than the average outdoor cat."

Do you have some sort of data to back this up?

I imagine that Retric (https://news.ycombinator.com/item?id=15228800) is referring to stories like https://www.washingtonpost.com/national/health-science/outdo... and https://www.nytimes.com/2014/03/22/opinion/sunday/the-evil-o... (DDG results for "outdoor cats wildlife death"), compared to, say, http://www.smithsonianmag.com/smart-news/how-many-birds-do-w... (DDG result for "wind turbine wildlife death").

This is likely unpopular (especially with cat people like me), but I'm not sure what's callous about it—unless you mean the "meh" part, in which case I'm not sure how backing it up with data makes it any less callous.

That's where the comparison comes from, however it's more that these articles are linking to harm without putting it into any perspective. If we replaced all electricity generation with wind farms you would kill fewer birds from pollution than the existing power plants directly kill.

There are 10+ billion birds in the US and a smaller but very large number of bats and well over 1 billion of them die every year. Talking about hundreds of bird/bat deaths in that context is almost meaningless.

PS: A fungus on the other hand is decimating bat populations and represents a real threat. However the actual threat is not exactly making the news. https://en.wikipedia.org/wiki/White-nose_syndrome

That made me wonder how bats see water surfaces. Though I suppose not seeing them is less of a problem since they're not vertical :P

The post explains this: they don't. Standing water exhibits the same behavior as reflectiveless flat surfaces.

When they fly over a space and "see" nothing beneath them, they interpret this emptiness as a flat, smooth body of water.

Thus the only real problem here is that for flat horizontal surfaces that aren't water, the bats will try to drink from them.

This is a good point. Perhaps the sound penetrates a distance into the water and you get scattering, returning a small signal.

Real life water surfaces are probably not as smooth as glass windows. Just a guess.

I had read this as Bots slamming into buildings, and was looking for a discussion of lidar and stereo vision systems.

But won't lidar have the same issue, with a clean glass surface? Similar with stereo vision - if there are no features at the surface to correlate.

Vision based on visible light doesn't suffer from the problem in the same way as echolocation or lidar, since it is not dependant on observing signals emitted by the observer. I guess very smooth surfaces might act as mirrors, which will probably bring it's own set of difficulties for machines. Anecdotally, I can say my own stereo vision doesn't have big difficulties with most smooth surfaces though :)

I know I have slammed into transparent surfaces because I couldn't see them.

It probably gets worse the higher you go, because there is less grassy people adding marks to them, and less "people are hitting this too much, we'd better reduce that glass size". Birds are famous for getting them wrong.

But bats also use vision based on visible light. I haven't read the article yet, but do they explain about why the bat wouldn't see the building with its eyes?

"researchers can rule out the possibility that the bats were visually confused, because the experiments were done under infrared light, which bats can't see, and so they would have been relying entirely on echolocation."

It might be nighttime.

Yes, lidar bounces off surfaces at shallow angles to give false readings. Also, the long wavelength of IR means that lots of flattish surfaces are good mirrors. In mobile robotics, glass panelled corridors are perceived very badly.[1]

Passive depth from stereo usually has big holes where no features are detected[2]. That's why Kinect and the like project their own IR texture into the scene. Outdoors ambient IR overwhelms the projection unless you use powerful lasers.

The upshot of this is that robots are vulnerable to banging into stuff, like bats.

[1] I don't know for sure but it's likely that the right hand side of this map I found online has glass walls causing bad range data: https://i.pinimg.com/originals/e0/87/04/e08704b6dc925b575c2f...

[2] If it doesn't, it's because the holes have been filled by interpolation - guessing what is there rather than observing it directly.

TIL Some Hawkmoths shoot ultrasound from their junk to thwart bat attacks. http://www.pnas.org/content/112/20/6407.full.pdf

I wonder how bats perceive the AT&T "Batman Building" in Nashville, TN.


I hope someone doesn't use this as inspiration for an exploit against LIDAR. On second thought, I hope people do start working on an exploit, so engineers can get on with hardening systems against it!

I built a number of robots that use infrared distance sensors for object detection and collision avoidance. Sadly the stereo cabinet I had made myself and painted flat black appeared invisible to them. Several robots ran into the cabinet at full speed :-(. The mitigation was to add another sensor (ultrasonic) which was better at seeing solid surfaces (but same problem as the bats for off angle approach).

The use cases I know of for lidar don't usually include a glancing reflection off a large flat surface.

Colliding with a large angled piece of sheet material in the middle of a roadway doesn't sound pleasant.

While I agree that the sensor systems should image just about anything you can imagine, wouldn't a large angled reflective sheet produce a shadow that could be distinguished from normal road surfaces and avoided?

That's a good 1st cut. But if we review the prior art -- namely stage magic's tricks with mirrors -- what's to stop someone from putting something in the region of the reflected image that would be expected by the driving AI? So, if what's expected are bushes in the background, why not aim the mirror at other bushes at the right distance?

Interesting hypothetical to track bat evolution in urban areas over time to determine if selection is occurring for bats whose sonar is more finely attuned for detecting diffused returns as actual signal for skyscrapers or, for that matter, improved actual sight to avoid the buildings in the first place.

Bats already have very good vision. They just can't see well in the dark.

Is probably more a case of blinded by electric lights here.

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