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.
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.
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.
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.
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.
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.
(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.
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:
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.
> 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.
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.
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.
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).
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:
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.
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.
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.
[+] [-] nether|12 years ago|reply
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.
[+] [-] jhonovich|12 years ago|reply
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.
[+] [-] slowmover|12 years ago|reply
http://www.worldofhummingbirds.com/migration.php
[+] [-] anonymous|12 years ago|reply
[+] [-] interstitial|12 years ago|reply
[+] [-] seszett|12 years ago|reply
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.
[+] [-] xuhu|12 years ago|reply
What also counts is wing size relative to air swirls/bubbles/thermals ... turbulence in general.
[+] [-] samatman|12 years ago|reply
[+] [-] cadab|12 years ago|reply
[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.
[+] [-] unwind|12 years ago|reply
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.
[+] [-] fhars|12 years ago|reply
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.
[+] [-] nether|12 years ago|reply
[+] [-] alphakappa|12 years ago|reply
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.
[+] [-] deltaqueue|12 years ago|reply
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.
[+] [-] seszett|12 years ago|reply
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.
[+] [-] rtkwe|12 years ago|reply
[+] [-] aaron695|12 years ago|reply
What is really needed is access to the raw data.
[+] [-] 205guy|12 years ago|reply
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...
[+] [-] antsar|12 years ago|reply
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.
[+] [-] Someone|12 years ago|reply
[+] [-] takluyver|12 years ago|reply
[+] [-] wikiburner|12 years ago|reply
http://lasvegas.cbslocal.com/2013/10/07/aerospace-company-de...
[+] [-] argumentum|12 years ago|reply
[+] [-] ccleve|12 years ago|reply
[+] [-] PhasmaFelis|12 years ago|reply
[+] [-] Ellipsis753|12 years ago|reply
[+] [-] cjensen|12 years ago|reply
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.
[+] [-] piokuc|12 years ago|reply
[+] [-] davorak|12 years ago|reply
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.
[+] [-] texasCoder|12 years ago|reply
http://en.wikipedia.org/wiki/Sleep_%28non-human%29#Sleep%20d...
Comparative average sleep periods for various mammals (in captivity) over 24 hours
Glad the avg sleep period of humans in captivity has been measured...[+] [-] forgottenpaswrd|12 years ago|reply
[+] [-] GuerraEarth|12 years ago|reply
[+] [-] goblin89|12 years ago|reply
> 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.
[+] [-] X4|12 years ago|reply
[+] [-] tocomment|12 years ago|reply
It just physically couldn't store enough fuel to fly to fix months straight, right?
[+] [-] dllthomas|12 years ago|reply
By, say, catching airborne insects. Which is how swifts (and also swallows) typically feed themselves.