This Bird Can Stay in Flight for Six Months Straight | Hacker News Reader

This Bird Can Stay in Flight for Six Months Straight

blogs.smithsonianmag.com

271 pointsdanso74 comments

This is a HUGE outlier among birds capable of long endurance flight, if the data turn out to be accurate. The Alpine Swift is tiny, 2-ft wingspan and 0.2-lb weight. In contrast, the Albatross stretches its wings to 12 ft and weighs 20 lb, and can fly for up to a few days straight (longest known endurance). Similar for the Condor and Stork. The large wingspan minimizes induced drag and lets it glide extremely efficiently, just like the U-2. As bird wingspans decrease, flapping frequency increases and flight endurance decreases, as with pigeons, hummingbirds, and flying insects. Aerodynamically, flight is vastly less efficient at smaller scales because the air molecules remain the same size. There are physical justifications for long-endurance birds being huge, just as there are with long-endurance aircraft.

Data collection seems highly suspect. Collecting v_dot every 4 minutes seems insufficient for takeoffs/landings that probably take a few seconds. I wonder if this polling rate satisfies the Nyquist criterion for typical acceleration changes of the bird? Then they mention relying on the pitch angle to determine flight. How clear is this correlation? Birds attain pos/neg pitch in climbs and dives. They adjust their pitch on the ground as they walk, while picking up bits to build nests, and ducking down to feed their young. I look forward to seeing this undergo peer review as alphakappa mentions. This type of flight seems very unusual, but perhaps they manage to feed off insects enough to sustain themselves.

Since I know practically nothing of birds in depth, how do they sleep during these extended flights? Or is bird "sleep" something different?

Completely guessing here, but I suppose it's the same sort of involuntary control you have over your body during sleep that keeps you from wetting yourself or rolling off the bed in the middle of the night.

http://en.wikipedia.org/wiki/Sleep_(non-human)#Birds:

"A peculiarity that birds share with aquatic mammals, and possibly also with certain species of lizards (opinions differ about that last point), is the ability for unihemispheric sleep. That is the ability to sleep with one cerebral hemisphere at a time, while the other hemisphere is awake"

In other words: the brain has two CPUs, and they switch off only one at a time.

Early M7 variant? I'd sure like the creator to chime in and dismiss the work as a marketing gimmick.

I was more curious about how they eat and drink during extended flights.

Swifts catch insects in flight, so food isn't a problem. I think there are species which can extract all the water they need from their food, so they may be able to go without drinking.

Swifts drink in flight, you can often see them flying very close to the surface of water... a bit like water bombers.

> Aerodynamically, flight is vastly less efficient at smaller scales because the air molecules remain the same size.

What also counts is wing size relative to air swirls/bubbles/thermals ... turbulence in general.

"Data collection seems highly suspect."

My understanding is they collected every 4 minutes for 200+ days, which implies 72,000 measurements.

If there were 72,000 measurements and none of them found the bird stationary, that's a pretty good sign the bird rests extremely infrequently.

Also, they got measurements from three birds so they have 216,000 continuous non-stationary measurements. A stats guru might be able to figure out the effective reduced sample interval.

Unless they land for very brief moments to rest - as I've seen swifts do... in west africa.

Sample rate is everything.

Look - this lady can fly!!! (Neat photos, to boot...)

http://kotaku.com/this-lady-appears-to-be-floating-5950132

Yet a Ruby-Throated Hummingbird can fly 450 miles (20 hours) nonstop over water when migrating, which I've always found amazing.

http://www.worldofhummingbirds.com/migration.php

wikipedia says it average 3.5g... we should usem them as batteries.

http://jeb.biologists.org/content/178/1/39.full.pdf rates their muscles at 100-120 W/kg, and ~25% of body weight as flight muscles.

So, 3.5 grams of hummingbird would be ~0.1 Watt, or, for a 20 hour trip, 2Wh of capacity. On the other hand, a kg of hummingbirds could give you 600 Wh, or 2-4 times what LiOn gives you.

I would go for hornets or other nasty insects, though. That gives less hassle with the law and animal rights activists.

You can't actually say that it's "a huge outlier", simply because it's the only small bird for which we have such data.

There was never any reason to think swifts had sleeping patterns anywhere close to those of albatrosses, condors or storks. Albatrosses, condors and storks also all have vastly different behaviours and live in completely different environments.

There's also the common swift, who spends almost all its time in the air and absolutely never lands on ground, due to being unable to take-off -- its legs are too short and weak to do that. They only land on rock faces and take off by letting go. That's where they build their nests too. You can see them in a lot of cities actually -- high buildings are pretty much perfect for them to nest on.

I almost hesitate to say it, but I did read the article hoping to find the average airspeed velocity of a slightly-laden European-African swift. I feel as though the BBC would have included this important information.

From the study[1] here is an image[2] of the comparison between flying, gliding and resting.

[1]http://www.nature.com/ncomms/2013/131008/ncomms3554/full/nco... [2]http://www.nature.com/ncomms/2013/131008/ncomms3554/carousel...

Edit. Its a shame there no technical details of the sensor, I'd be interested in seeing how a device like this kept functioning over a year.

It only takes ones reading every four minutes, which probably pushes the duty cycle for the processor and sensor chips down enough to make the energy budget.

Assuming a slow 3 seconds for each cycle of "wake up, initialize sensor, take a reading, store it to flash, set timer, go to sleep", that's a duty cycle of 1.3% which is pretty nice.

> "wake up, initialize sensor, take a reading, store it to flash, set timer, go to sleep"

Actually, you can do all that in about 30ms.

Less, if you just save to RAM and then only write to flash when you have filled up your buffer.

Scientists generally don't want their data stored in volatile memory. If something goes wrong, they lose valuable data points.

If something goes wrong, the rest of the dataset will be missing anyway. I don't think it matters much if 25000 points are missing or 25100.

You can't typically write just 1 byte into flash - you have to write in pages of say 4KB.

And writing to flash is painfully slow.

So it's most efficient (current-wise) to store up 4KB worth of data in RAM and then write it all to flash in one fell swoop.

It's a tradeoff with data security, but I think it's a good tradeoff because only rarely will things go wrong, but the additional current burn is guaranteed and constant if you write every datapoint to flash.

Magnetic FRAM is making a comeback just to scratch some of these low-power itches. It's faster, uses less power, and has greater write endurance. TI even put it in one of their latest MSP430's.

I know, that's why I said "slow". :) I wanted to aim for a very "bad" estimate, just to make the point more clearly: the duty cycle is low for this system.

There could be a tiny pendulum generator, like in watches.

The large chip on the image seems to have a number starting with 16F (or maybe 18F), so it seems to be some PIC microcontroler in a 20QFN package. The other two black objects on the board seem to be the accelerometer and light sensor, there are loads of these available in these sizes from your favorite parts suppliers.

According to the (german) page https://pdb.bfh.ch/search/pdbwebviewdetail.aspx?lang=de&proj... they are currently working on a next version that does also include air pressure and magnet field measurements.

(Note, this is just a critique, not criticism of some obviously painstaking research)

It would be good to see the results after these experiments get peer-reviewed and replicated. Without just the information presented, it's possible to imagine issues. For example, data is collected every four minutes (We don't know for how long, but let's assume that it's for a few seconds to conserve power). Is it possible that when they are on the ground, they aren't completely still - will their motion on the ground be mischaracterized as flight?

It would be great if an altitude sensor could be practically added to the sensor package.

Pressure sensors don't really give a good measure of altitude from one sample. For starters weather can drastically change the pressure in a region. If a sensor package could somehow filter that out with a 4 minute sample rate (doubtful) then the sensor is still giving you altitude relative to sea level which means the data would have to have a GPS component to differentiate between on the ground on a tall hill or flying over a flat lowlands area.

You're right. So how else could this problem be solved given the power constraints?

(P.S. I do have to mention - It's very likely that my critique is completely invalid because they may have performed measurements of these birds in flight Vs. these birds on ground, and the accel data may show completely different characteristics for both. It's also likely that they may have chosen the sampling rate and data duration based on these experiments, but since this is HN, it's fun to speculate on how this experiment could be improved.)

Somebody else posted a link to this graph from the publications that shows results for different movement patterns actually observed while the birds were in the summer colony: http://www.nature.com/ncomms/2013/131008/ncomms3554/carousel...

how else could this problem be solved given the power constraints?

I wonder if gravity changes enough at a typical flight ceiling to be detectable by a very accurate accelerometer?

At 5km up the difference is miniscule, back of the napkin says the difference is ~-0.01 m/s^2. Which is pretty small to use as a classification filter. All the way up to 40km it's still only ~1.2% weaker.

With fish they have tags that record light intensity, pressure and temperature which is enough to give a low res position estimate [1]. Not sure how well this would transfer to this problem but it is cool tech.

[1]: http://www.gtopppublications.org/repository/254_07-11-11_Blo...

Mostly a nitpick, but pressure sensors don't give a good measure of absolute altitude ever, regardless of the number of samples. You must calibrate it using pressure measurements from a ground station nearby in space and time, or else it tells you roughly nothing.

Weather matters a lot, as you say. The variation caused by weather can be equivalent to several thousand feet of altitude. Worse, changes due to weather are long-term. You can't filter them out, period. Samples taken four minutes apart can tell you changes in altitude, since the weather won't change that much in such a short time, but there's no way to backtrack to absolute altitude without calibration, no matter how many samples you take.

True. However if we're looking for very brief landings followed by periods of flight you might see that in the pressure data.

You'd expect some flat "flight level" pressure over a day, with V pressure changes to correlate with landings (or swoops in mid-air). You would need to correlate these with other sensors for it to mean anything concrete but it could corroborate or disprove other theories.

Right, but you couldn't distinguish a V that was a brief landing from a V that was a dive and climb, nor could you distinguish a flat line that was cruising from a flat line that was sitting on the ground.

I don't doubt that pressure data would be useful, it just doesn't give you altitude data.

My first thought would be to scoff at your criticism. Would the birds' travel patterns be any less impressive if they were resting for very short periods during these 200 days? The sensor measures acceleration, so the only potential confusion might be with light movement near ground / trees.

But according to another study, some migratory birds rest for only seconds at a time during their flights:

http://www.livescience.com/1045-migrating-birds-hundreds-dai...

At 4-minute intervals over 200 days, you have 72,000 datapoints. There are 1,920,000 9-second intervals (avg nap period from other article) over 200 days, so given their data collection spans only 3.75% of this time there's a chance they missed one of these naps.

Nevertheless, this is still very interesting.

That got me curious, so I ran the numbers on the chances they'd miss all of the naps; assuming these birds take only one 9-second nap a week (28 naps total over 200 days) there's a 35% chance the researchers would have missed all of them ((1 - (28 / 1920000)) ^ 72,000), which is pretty reasonable. But that chance goes down to 8% for one nap every 3 days, and to 0.055% for one nap a day. I'd say maybe one 9-second nap every few days is the lower limit of what I'd find plausible (assuming this was run for only one bird).

EDIT: Ah, missed this in the article - they were three birds. So the chances they'd miss all naps for all three birds goes down to 0.055% for one nap every three days, and 4% for once a week. So 9 seconds once a week is barely believable, but if they can reproduce this with another couple of birds that becomes really unlikely.

Those thrushes don't land to just nap for 9 seconds and then take off. They sleep for 9 seconds during a longer rest period, because they have to stay alert. They can't fly during the day because of airborne predators.

"My first thought would be to scoff at your criticism. Would the birds' travel patterns be any less impressive if they were resting for very short periods during these 200 days?"

The criticism isn't aimed at the birds; it is aimed at the logic of the researchers. The critic claims their conclusion does not follow from their data.

> Is it possible that when they are on the ground, they aren't completely still - will their motion on the ground be mischaracterized as flight

Well, actually swifts can't even walk and have a very hard time taking off from ground. I don't know their behaviour once in Africa, but while they're in Europe you only ever see them in flight, on phone cables or clinging on cliffs. They fly straight to and from their elevated nest. I doubt very much that these situations would look the same as flight.

Also... I think you guys could just try to have a little bit of trust in the knowledge of people who obviously know swifts better than you do. I think you can trust them for having studied their data a bit.

Dude. Asking questions and offering constructive criticism is how we understand good science, improve bad science, and discern the one from the other. "Having a little bit of trust" instead of asking questions is exactly what scientists should never do.

The people in here who ask questions aren't scientists. Asking "but are you sure the sequence shows flight and not moving on the ground" for a bird that is widely known to never touch the ground is not constructive criticism, not good science, it doesn't improve anything, it just distracts from pertinent questions from knowledgeable people.

Good science is criticism from people who have some knowledge in the field. Otherwise you're no better than the client who tells the designer that making the page title blink would add a nice touch to the homepage.

> Asking "but are you sure the sequence shows flight and not moving on the ground" for a bird that is widely known to never touch the ground is not constructive criticism

"Widely known"? Are you reading the same article? No one had any idea this happened until this study.

(Yep, double post. Too late to delete. Sorry.)

> Asking "but are you sure the sequence shows flight and not moving on the ground" for a bird that is widely known to never touch the ground is not constructive criticism

"Widely known"? Are you reading the same article? No one had any idea this happened until this study.

Minor point -- swifts don't perch on phone cables. That would be swallows and martins (unrelated). Swifts only land on the sorts of sheer rock faces / buildings that they nest in AFAIK.

Final random swift observation: you can see some swift species hovering very briefly to take nectar from flowering trees which is cool, seeing as molecular and other evidence shows hummingbirds to be their closest extant lineage.

I think it has been peer reviewed? http://www.nature.com/ncomms/2013/131008/ncomms3554/full/nco...

What is really needed is access to the raw data.

Like others, the tech is really promising, and it would be useful to have more info.

I also think it's fascinating how the advanced tech is allowing scientists to gain more insight into the animal behaviors that are all around us, yet still unknown.

Another migratory bird feat is the Pacific golden plover[1] that fly from Alaska and Siberia to Hawaii and New Zealand over several days. The incredible thing is that after raising their young in the north, the parents fly south without them. The young birds fly south by themselves and find the islands by themselves (presumably). There is much unkown about this migration, and these sensors would be very helpful.

[1] http://www.kilaueapoint.org/education/naturefocus/hnf3/index...

Worth noting:

The tags only collect data every four minutes, so it’s impossible to rule out the chance that they touched down occasionally in between these intervals—but every single one of the data points collected for more than six months in a row indicated that, at the time, they were either actively flying or at least gliding in the air.

A different species, a different insane record, and different technology, but also discovered only because of advances in the miniaturization of electronics: some arctic terns fly 90.000 km in about 9 months (http://ardea.nou.nu/ardea_show_abstract.php?lang=uk&nr=4099).

Nice. To convey the scale better: that's the equivalent of flying twice around the world.

Even better, that's not just the equivalent but they actually do fly around the world - ok, not two straight flights around the world, but from the Arctic to Antarctica and back!

Slightly related, but here's a recent article on a "Drone That Can Fly Continuously For 5 Years". I think this was submitted recently and didn't take off, but it's pretty interesting:

http://lasvegas.cbslocal.com/2013/10/07/aerospace-company-de...

This is awesome .. also ironic that on the #4 and #6 stories on HN right now are these:

  *This Bird Can Stay in Flight for Six Months Straight*

and

  *Aerospace Company Develops Drone That Can Fly Continuously For 5 Years*

What's more likely: a bird that can fly for six months straight, or a software bug that caused the sensor to yield misleading data on what the bird was actually doing?

How likely would you say it is for an air-breathing mammal to spend its entire life in the ocean? It would need to be swimming all the time, even while it slept, to avoid drowning.

Awesome article and very interesting. However to go on a bit of a tangent what did people think of the sensor in the photo? It's interesting that such as small sensor still has long pads for connecting (presumably to program it and get data off) and also that it has a little tag on the left of the picture (making it bigger). I can't see a battery in the photo. Is it on the backside or is it powered in some other way? Also what is the little metal wire for? I would think that it was an antenna, however they state that they had to find the birds again to get the data back so it would seem that they don't communicate wireless. Could it be getting powered from radio waves instead? What do you think? Is there more information on it somewhere?

The interesting thing to me is why? What would cause this evolution? Most swifts fly all day and can barely perch, but they do perch for the night since they require sight to locate aerial insects and the effort of flying all night is a big energy drain on a small bird.

I can think of only two possibilities: First possibility is that insects are dense enough that they are feeding themselves at night. Second is that the safety of being off the ground plus abundant daytime food makes this a better survival strategy.

Can't wait to see what the ornithologists come up with to explain this.

Watch migration of eagle Arnold from Slovakia to (probably) South Africa, on a google map: http://spravatanap.sk/web/index.php/component/content/articl... The page is in Slovakian but Google translate does a good job.

Article at nature website: http://www.nature.com/ncomms/2013/131008/ncomms3554/full/nco...

Scroll through the figures here: http://www.nature.com/ncomms/2013/131008/ncomms3554/fig_tab/...

I could not find the raw data at a glance or the elevation over time which would have been useful to see if there were any likely points where it could have landed and taken off again between data points.

From the linked wiki article describing sleep in non-humans:

http://en.wikipedia.org/wiki/Sleep_%28non-human%29#Sleep%20d...

Comparative average sleep periods for various mammals (in captivity) over 24 hours

    Horses – 2.9 hours
    Elephants – 3+ hours
    Cows – 4.0 hours
    Giraffes – 4.5 hours
    Humans – 8.0 hours

Glad the avg sleep period of humans in captivity has been measured...

Great animals. It is spectacular seeing them flying in big groups. They are also very useful for controlling mosquitoes.

Since the birds can sleep with just one cerebral hemisphere dormant at a time, rest while gliding, eat and drink while airborne--and it is much safer in the air than on land, it actually makes more sense for the birds to remain aloft. It's just different than what we (can)do.

A sceptic in me suggests that new sensors could exhibit some sort of unexpected behavior that skewed experiment results.

> Perhaps most exciting is the fact that this finding came after just the first time the new, ultra-lightweight movement sensor was used in avian research.

Swift Rescue: Saving a Protected Alpine Swift, Stuck Atop a Six-Story Building (HD) – http://www.youtube.com/watch?v=T83EHM_rUlw

I feel like this wouldn't jibe with conservation of energy. Unless the bird can eat in the air somehow.

It just physically couldn't store enough fuel to fly to fix months straight, right?

"Unless the bird can eat in the air somehow."

By, say, catching airborne insects. Which is how swifts (and also swallows) typically feed themselves.

Psh, any bird can stay in flight for 5 years if aboard this drone: https://news.ycombinator.com/item?id=6528598.

Seems like this would make for a great model for long endurance UAVs

Make the UAVs refuel by eating insects in the air?

Or ride thermals.

Don't be silly. UAVs eat micro-USVs.

"For more than 200 straight days straight"

as opposed to 200 straight days on the sauce?

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