Wikipedia:Reference desk/Archives/Science/2015 April 29

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

April 29

Mourning dove sounds

Mourning dove#Sounds says "In flight, the wings make a fluttery whistling sound that is hard to hear. The wing whistle is much louder and more noticeable upon take-off and landing". How does this sound get produced? Nyttend (talk) 14:36, 29 April 2015 (UTC)

See (and hear) e.g. here [1]. These science papers discuss the role of the wing whistle as a form of communication both within and between species [2] [3] as an alarm signal. As for the actual mechanism, it's sort of like a Bullroarer -it's just the wind whistling through the feathers, much like you may hear the wind whistling through certain fences - most birds' wings make some sounds when they fly. Some, like the owl, have pressure to fly as quietly as possible. Others, like the doves, have found it beneficial to have a more pronounced sound available. Anyway, the key recent review seems to be "Mechanisms of feather sonation in Aves: unanticipated levels of diversity KS Bostwick - Acta Zool. Sin, 2006" - freely accessible here [4].

(WP:OR There are currently dozens of doves in my yard on a daily basis. They make the wing whistle more when actually startled, compared to when they just decide to take off and forage elsewhere. Once the doves' wings whistle, most other birds in the yard also spring up, with possible exception of the entirely-too-bold-for-my-taste great-tailed grackles. )

I have updated mourning dove to include a link to sonation, it would probably be an improvement if someone wants to add some explanation about alarm signaling, using the refs to the first two articles I linked above.SemanticMantis (talk) 15:15, 29 April 2015 (UTC)

Race and outgroup homogeneity

I have often heard some individuals say that members of a different race look alike, and they easily mistake an individual for someone else because that individual is not part of their race. In contrast, when I look at people, I notice that every individual looks different, even when they do not share my racial background. Is outgroup homogeneity related to prosopagnosia, giving some individuals the ability to distinguish different faces while other individuals may struggle at this task? 140.254.70.33 (talk) 15:01, 29 April 2015 (UTC)

Link to Prosopagnosia. Bus stop (talk) 04:05, 1 May 2015 (UTC)

Wikipedia has articles titled Out-group homogeneity and Cross-race effect which you can read. One thing to remember about these concepts, they are descriptive and probability based phenomena. What they do not do is expect uniformity of individual results or mechanism. That is, the concept allows you to say what usually happens, not that the same things happens all the time, nor does it in any way describe why something happens, just that it does. Thus, in most people, they have a greater ability to distinguish individuals who look most like themselves, and less ability with people who look significantly different from themselves. That does NOT mean that EVERY person is identical with regard to this property, NOR does it mean we can explain what causes this to happen. So when you ask a question along the lines of "Why doesn't this work for me", there are two reasons it can't be answered. One is that there's no guarantee it will work for you. If it doesn't, we can't even say why you're different, because we don't have a mechanistic cause. There is some correlation between outgroup homogeneity bias and living in ethnically isolated areas, many studies have shown that people who grow up in more ethnically diverse areas show less bias in this regard. See here for an example, which discusses the difference in the bias between children attending ethnically heterogeneous schools vs. those attending single ethnicity schools. One can find similar studies across the board. So, if perchance, you grew up in an area with people from lots of different ethnic backgrounds, that may lead you to have less bias than someone who grew up surrounded only by a single ethnicity. But again, that's only talking likelihoods, not certainties. If you say "Nope, I grew up where everyone I knew was all a single race", it still doesn't invalidate the concept, nor does it invalidate your experience. Sometimes, people don't fit the models. --Jayron32 16:30, 29 April 2015 (UTC)

• An anecdote you can take for what it's worth. Having grown up in a town that was 97% white, non-whites looked similar enough to each other to me that I certainly understood the "they all look the same to me" phrase. Then, after living and working mostly with blacks and hispanics since high school, I note non-white diversity much more keenly, to the point that I feel odd in areas that are "all white", and more at ease when I'm back in NYC. μηδείς (talk) 18:51, 29 April 2015 (UTC)

• I'll confirm Medeis's experience as similar to my own. I grew up in a state which literally (not figuratively-literally, but yes-honest-to-goodness literally) had less non-White people than the current school I am a teacher in right now. I can say that my experience has changed as well by being exposed to different races. In both the neighborhood I live in and the school I teach in, I (a white person) am a local minority. It does change your experience. --Jayron32 02:13, 30 April 2015 (UTC)

Predation in human history

Since when did humans become apex predators? If other predators (bears) eat a human carcass, does that remove humans from apex predator status? If a human being gets lost in the wilderness and away from villages that may otherwise provide safety and society, then will he or she become susceptible to natural predators? 140.254.70.33 (talk) 16:18, 29 April 2015 (UTC)

It isn't that humans are apex predators, per se. It's that we removed ourselves from the predator-prey relationship by animal domestication; we don't really hunt so much as we grow our meat. So the answer is "We didn't win the game, we stopped playing the game". --Jayron32 16:32, 29 April 2015 (UTC)

Additionally, scavenging a carcass does not make one an apex predator. Vultures do not remove lions from being an apex predator if they eat their carcass. Removing a predator from its niche conditions and making it abnormally vulnerable also doesn't make it not an apex predator. If a lion wonders outside of its normal area or the whether suddenly, but briefly, changes, making it vulnerable to another predator, I don't think it could be said to lose its apex predator status just from that short period. Humans, when acting as predators (hunting rather than domesticating) have created a niche where we are largely not under extreme threat, but can take down basically anything else that we want. --OuroborosCobra (talk) 17:10, 29 April 2015 (UTC)

And even if humans suddenly lost all ability to distinguish between homophones, we would still not lose our niche. :-) StuRat (talk) 18:47, 29 April 2015 (UTC)

And on point here:

User:Sophocles wrote

Wanders [Ed: surely shome mistake?] are many on earth, and the greatest of these

Is man, who rides the ocean and takes his way

Through the deeps, through wind-swept valleys of perilous seas

That surge and sway. ...

They aren't homophones to me. "Wander" and "Wanda" are homophones to me, but I suspect not for you.

StuRat, feel free to ignore my intrusive question about your personal life, but are you rhotic?

Pete AU aka --Shirt58 (talk) 11:01, 30 April 2015 (UTC)

I have the bizarre habit of pronouncing an R when I see one, and not, when I don't. StuRat (talk) 17:09, 1 May 2015 (UTC)

(More a rant than an answer; technical works tend to be more careful than this...) "Predator" is a very crude classification for an infinitely diverse range of behavior, and so it will always be an approximation; the same is true of "apex" predators. The theory is that nothing preys on the apex predator. Presumably that means that the apex predator has no selective pressure acting on anti-predator adaptations. Yet usually the apex predator is only in that position because it has such adaptations, whether they be as simple as being big and having nasty teeth or as complex as the mechanism by which electric eels appear in the gallery on apex predator. And since such adaptations are not lost to genetic drift, it follows that there is not truly a lack of selective pressure, i.e. not a total lack of predation. So the approximation cannot be made perfect: the apex predator's yang has to have a little bit of yin in it to exist at all. If humans are an apex predator, why are we afraid of wolves? Because if we weren't, we wouldn't be. Wnt (talk) 19:55, 29 April 2015 (UTC)

Why does water moving inside a water pipe make noise?

Why does water moving inside a water pipe make noise? — Preceding unsigned comment added by 223.83.207.66 (talk) 17:49, 29 April 2015 (UTC)

Without you being more specific, I expect your referring to gurgling sound due to entrapped air. There is also water hammer (banging). Then there is fluter (tap washer) and a repeating sound caused by ball-cocks. If you watch old moves, a regular taping sound that incorporates a pattern, is probable your next-door prison cell-mate sending you Morse code. (E.g. 'ere Rocky, I'm due to fry to morrow – can you spare a quarter for the electricity meter.?)--Aspro (talk) 18:26, 29 April 2015 (UTC)

The general reason is because the motion of water has friction, that creates vibration in the pipe (and water, and air) that results in sound. Let us know if you need further help. There are several ways water in a pipe that can produce sound, Aspro has given some of those above, but they all come down to vibration and impulse in the physical matter. Water hammer, Aeroelasticity#Flutter, and Ballcock linked for reference. SemanticMantis (talk) 01:27, 30 April 2015 (UTC)

Also Turbulence (c.f. Laminar flow). --Jayron32 02:20, 30 April 2015 (UTC)

I understand Cavitation is also a source of noise around bends, valves, cocks etc. wherever the flow is constrained.Dolphin (t) 11:55, 30 April 2015 (UTC)

Major earthquakes distribution

Does the probability of a next earthquake increase by the long absence of earthquakes? Given a situation were there are no little hints like foreshocks or smaller earthquakes that anticipate a bigger event, can we calculate a probability that is better than random data? Or are big events completely randomly distributed and unrelated in time? --Llaanngg (talk) 22:06, 29 April 2015 (UTC)

Earthquake prediction--Aspro (talk) 22:34, 29 April 2015 (UTC)

There is nothing there about the probability distribution, although the articles discusses other methods of predictions, which I excluded from the answer.--Llaanngg (talk) 23:45, 29 April 2015 (UTC)

Look at plate tectonics, subduction zones and slip faults. The mere fact there hasn't been a quake for a long time in itself doesn't make a quake more likely if the reason is there is no geological fault for the quake to occur. But yes, in general the longer stress has built up at a fault, the more likely a quake becomes. Watch any of the Nat Geo documentaries at youtube on megathrust quakes for fun basic science. μηδείς (talk) 02:31, 30 April 2015 (UTC)

@Llaanngg: A useful search term is conditional probability - for a given location, say the San Andreas fault, it seems that the time since last earthquake can affect the probability of an earthquake. See e.g. this paper, which derives some estimates for conditional probabilities [5]. SemanticMantis (talk) 14:13, 30 April 2015 (UTC)