Wikipedia:Reference desk/Archives/Science/2014 August 20

= August 20 =

Wheel base anf friction
Can we say that wheel base is proportional to friction acting on a vehicle,when brakes are applied.I think i solved a problem in h c verma(12 class physics) using this assumption.please correct me if i am wrong.

Sameerdubey.sbp (talk) — Preceding undated comment added 03:38, 20 August 2014 (UTC)


 * Wheelbase is normally understood to mean the distance between the front and rear axles of a vehicle. Your statement accordingly makes no sense at all. AndyTheGrump (talk) 03:41, 20 August 2014 (UTC)

I appreciate your effort in commenting Grump.See google bookpg 371,there's a derivation that has wheel base in numerator and denominator as well.Then what do you say?whether frictional force would increase or decrease with wheel base. please read derivation and then comment.Bit engineeering involved. SD — Preceding unsigned comment added by Sameerdubey.sbp (talk • contribs) 07:12, 20 August 2014 (UTC)


 * Link is broken. yes there is a bit of physics involved, that's a high school physics problem judging by the search terms, but your question is at best very misleading, but answering the most likely rendition, you are wrong. Greglocock (talk) 07:55, 20 August 2014 (UTC)

Mr cock ,justify whatever you want to say.let it be high school physics. SD — Preceding unsigned comment added by Sameerdubey.sbp (talk • contribs) 09:58, 20 August 2014 (UTC)


 * [ was able to get the link to work, but google books is notoriously hard to link to... try this one maybe.
 * Anyway, as far as I can tell, the OP's claim is sound, if we understand it not to be about friction per se but the retardation in speed as the book calls it. The book uses D'Alembert's_principle to calculate the retardation of applied brakes in a three scenarios, 1)rear brakes, 2) front brakes, 3) all four wheels.
 * Basically, the wheelbase L comes into play because the car is going up an inclined plane, and the the brakes are only applied to the rear wheels in that example. This setup effectively creates a moment arm due to the fact that the center of gravity is above the plane containing the centers of the wheels. This should make intuitive sense: if the car is going uphill quickly, then brakes only using rear brakes, the car will start to lift at the rear, thus reducing the normal force on the rear wheels, thus diminishing the effect of braking. Using a very long wheelbase truck, e.g. a Ford F-650, this effective decrease in retardation will have lesser magnitude, compared to e.g. the same effect in a Mini.
 * Likewise, L appears in the solution to the front brakes only.In the later example of all four wheels braking, no L term appears. This book contains a bunch of fairly complicated and analyses of force diagrams, including some bothersome algebra and calculus. So, while not terribly "hard" math, it's more than I can work through and explain in a few minutes, which is all I have to spare right now :)
 * So, OP, you are not entirely wrong, and I'd give a gentle trouting to the above posters for assuming you were wrong without really looking for how you might be right! I still can't tell what your specific question is, nor can I check your answers. But the idea that the effect of braking, "retardation", can depend on wheelbase, is sound, provided that we are interested in the case of an inclined surface and brakes not applied to all wheels (or with different types of brakes on front and rear wheels, which used to be common). As the equations show, wheelbase can affect retardation in that scenario, but it is still incorrect to say the wheelbase is directly proportional to the retardation, because you cannot factor equation 8.24 into the form a=L*(a constant term), where a is the symbol for retardation. Hope that helps, SemanticMantis (talk) 17:43, 20 August 2014 (UTC)


 * Trout all you like, " wheel base is proportional to friction acting on a vehicle,when brakes are applied" is wrong. If you double the wheelbase of a typical vehicle (say cgz=0.7m, wb=2.6m) on a typical slope (up to say 0.25) then the frictional braking force at any axle is NOT doubled. Do the physics, no calculus required. The OP asked if he was right or wrong, he is wrong.Greglocock (talk) 22:13, 20 August 2014 (UTC)
 * Well, I did say a gentle trouting :) and I did specify that it is not correct to say that it's directly proportional. I'm assuming OP doesn't have English as a first language, and is also learning new physics. And based on the ref OP provides, it is true that wheelbase can affect braking effectiveness if not all four wheels have equal braking power. The equation in the book gives for rear-wheel breaking up an incline is $$ a_{retartadion}= \frac{(L-x)(\mu g \cos \alpha)}{(\mu h +L)} + g \sin \alpha$$. True, that is not what we call directly proportional, but there is a near linear dependence there. For certain values of the parameters (e.g. large L>>1, x <<1, 0< sin \alpha <<1 ), it is very nearly proportional. I mainly brought up trouting because I assumed from your response that you didn't even look at the OP's link before responding. SemanticMantis (talk) 00:20, 21 August 2014 (UTC)

Semantic is the man,thanks a lot!!,It means,i said the reverse.while riding a vehicle,without the brakes applied.I must say wheelbase is inversely proportional(Third Case) to the retarding force acting to bring vehicle to motion or keep it in motion.since braking force is proportional to (mu*constant/L),where L is the wheelbase(See the third case in Bookpg347).Now as L increases opposing force or braking force on vehicle decreases.Hence Low wheelbase vehicles are harder to bring into motion and less fuel efficient.Is it the thing Practically,i feel the reverse.What do u say? Mr.Cock be Human. — Preceding unsigned comment added by 121.242.75.225 (talk) 03:18, 21 August 2014 (UTC)
 * I think you need to be careful about generalizing from the math shown in the book. While fairly detailed, this is still very much an idealized representation of car physics. Equation 8.26 is the conclusion of third case, where all four brakes are applied equally, and no L terms occur. There are L terms in the previous lines, but they eventually cancel out. I think L will only come into play for braking two wheels at a time, which isn't very common in the real world. I don't think this analysis will help you draw any conclusions about cars with small wheelbase being less fuel efficient. In the real world, smaller cars tend to be more fuel efficient in terms of miles per gallon, because they usually weigh much less. If you factor weight into your idea of efficiency, then perhaps some larger cars have a higher (miles)*(weight)/gallon. But for real world scenarios, there are far more details than included in your linked book. This is why things like mpg are tested empirically, not calculated from first principles of physics. Anyway, I hope I've helped clear up this example. If you have more questions I'd probably recommend starting a new thread, and spending a little more time composing your English. While I can understand you, it is a bit difficult to do so, and some people make the mistake of thinking poor English means the writer is not that smart ;) SemanticMantis (talk) 14:27, 21 August 2014 (UTC)


 * Actually due to tire load sensitivity in the real world there is always an L term present even with 2 axles braking and on a flat road, that is, weight transfer always matters. Greglocock (talk) 00:27, 22 August 2014 (UTC)

Velocity of Saturn's moons
Any of the many, doesn't matter - I'm writing a fantasy where there's a vehicle tethered to one of Saturn's satellites, towing it around one of the rings. My preference is for one of the Inuit, Gallic, or Norse moons, because their names are so cool, but I gather they're further out than the orbit of the rings.

Thanks for your indulgence

Adambrowne666 (talk) 04:42, 20 August 2014 (UTC)


 * Velocity relative to what? Saturn?  If one end is tethered to the satellite, what's the other end tethered to?  (It can't be Saturn, because it doesn't have a solid surface.)  --Bowlhover (talk) 05:06, 20 August 2014 (UTC)


 * Note that if you have a tether running from the spacecraft to the moon, remember that you only need the tow to get the vehicle up to the speed of the moon - then you can cut the tether and the spacecraft will continue to follow the moon around. Of course the moon will have some tiny amount of gravity - so after that initial acceleration, you'd pretty much have a slack tether.  So calling this a "tow" is a little confusing. SteveBaker (talk) 05:20, 20 August 2014 (UTC)
 * The statement that Saturn doesn't have a solid surface isn't entirely correct. Like Jupiter and the other gas giants, it does have a nickel-iron core, surrounded by a layer of ultra-dense hydrogen metal. The metallic hydrogen is probably a liquid, but the nickel-iron core is presumably definitely solid, and certainly has a surface. Saturn is mostly hydrogen all the way down, so the prevailing theory is that changes in pressure mean that the metallic core is surrounded by a giant hydrogen sea just beneath the gaseous layers we're familiar with. According to our article on Saturn, the transition from gaseous to liquid hydrogen occurs at such an altitude that 99.9% of Saturn's mass is within the pressure range for liquid hydrogen&mdash;so maybe we should be calling it a liquid giant. As an aside, some scientists now think that Jupiter and Saturn's magnetic fields are largely produced by this massive amount of metallic hydrogen, rather than by their fairly small nickel-iron cores.
 * Given strong enough materials, you could easily utilize the principle behind Clarke's space elevator to either tether something directly to the solid core, or to a buoyant object floating in that sea. Evan (talk&#124;contribs) 15:54, 20 August 2014 (UTC)
 * This must be some meaning of the word "easily" of which I was previously unaware. SteveBaker (talk) 19:08, 20 August 2014 (UTC)
 * I am assuming, of course, that someone wants to spend the money necessary. Space elevators are completely possible given current technology; a simple tether (read: spaceworthy bit of string) would be even easier. Evan (talk&#124;contribs) 19:33, 20 August 2014 (UTC)
 * No, space elevators are impossible with current technology, even on Earth. The only known material strong and light enough is carbon nanotudes, and it's not currently possible to make more than a few centimeters of it.  See space elevator.  --Bowlhover (talk) 05:19, 21 August 2014 (UTC)
 * I've read the article, but I think we're talking past each other. Carbon nanotubes seem to be the technology practical space elevators will require; the problem is manufacturing them in large enough chunks for a construction process of that magnitude. I look at that as a manufacturing (and not insignificantly, a funding) problem. I might have too much faith in science, but I struggle to imagine the world's scientific community failing to work out the manufacturing difficulties, given access to Apollo-project-style funding. "Impossible" is a strong word; "hasn't been done yet" is more appropriate. As an aside, space tether is another fun article. Evan (talk&#124;contribs) 18:53, 21 August 2014 (UTC)
 * Which is totally irrelevant anyway, as I just noticed. Adam specifies that the satellite is tethered to a vehicle (though perhaps vice-versa would be more appropriate), and I'm thinking that means the vehicle is either in orbit around the satellite or trailing behind it (being towed) in the same orbit around Saturn. If the latter, then what you're looking for is the orbital velocity of whichever moon you'd like to use&mdash;meaning the moon's velocity relative to Saturn&mdash;since a perfectly tethered object would, of course, attain the same velocity relative to Saturn as the body towing it. If the former, then you need to find the moon's escape velocity&mdash;i.e., the minimum speed an object must achieve to escape the surface and enter an orbit around that moon&mdash; There are probably orbital velocities listed for most or all of Saturn's moons... somewhere. And keep in mind that the easiest orbital tether is going to be one with the "space end" in geosynchronous (lunosynchronous? selenosynchronous?) orbit, so that is probably the number you want. Evan (talk&#124;contribs) 16:29, 20 August 2014 (UTC)


 * The only reason I can see to "tow" something "around the rings" is if you want it to move at a speed different from that of the ring particles (without constantly expending reaction mass), so I'm guessing you mean to hang your vehicle from a body in higher orbit? So you want to divide the circumference of a ring orbit (2&pi;&times; the radius of some circle in the ring) by the period of whichever moon you use as the anchor, and that gives you the speed. —Tamfang (talk) 01:17, 21 August 2014 (UTC)


 * I'm not too sure about the antecedents, but this does seem like a clever use of a space elevator, or really, a space tether. Because the gravity of Saturn's moons is so small, very little tensile strength is needed for a short distance - of course, if you're laying 500,000 km of cable from Rhea (moon) to somewhere deep in the atmosphere of Saturn, then no standard-issue nanocarbon space elevator cable would be sufficient.  But if you're just looking to hang off some shepherd moon and scoop up chunks of ice out of the rings for whatever purpose you have in mind (batting practice???), my guess is you can do it with plain steel.  (Though I'm too lazy to work the math)  The advantage of using a moon is that you don't need to worry about a counterweight; the moon is so heavy that its equilibrium will be little altered by the hanging cable. Wnt (talk) 22:23, 21 August 2014 (UTC)


 * The orbital speeds of Saturn's moons can be calculated from the table in Moons_of_Saturn. Multiply the orbital radius by 2*Pi, then divide by the orbital period to get the speed in kilometers/day.  (Multiply the result by 24 to get kilometers/hour).--Wikimedes (talk) 08:23, 22 August 2014 (UTC)

Can a shooting cause gradual brain death?
Hello. In a script I'm writing, a character is mortally wounded by gunfire. After a protracted period, the character suffers brain death. Is this plausible? I've read some articles on the subject and I'm not entirely sure how a bullet wound would lead to slow brain death. 73.184.21.12 (talk) 05:36, 20 August 2014 (UTC)


 * Your question is misleading. If a human is suffering from a gunshot wound. The human will suffer from a slow brain death while they are also suffering from a slow liver death and a slow death for every part of their body. The blood system in a human body is for all parts of the human organ. So technically yes, the character will suffer a slow brain death. 202.177.218.59 (talk) 05:59, 20 August 2014 (UTC)

Thank you for the response. I've been doing mental gymnastics trying to figure out how a person's brain would die slowly from indirect bullet wounds a la drowning, while idiotically overlooking the fact that the whole body would slowly succumb from such an injury. 73.184.21.12 (talk) 06:28, 20 August 2014 (UTC)
 * In general terms, this would be the basis for the notion of charging Hinkley with murder 34 years after the fact. ←Baseball Bugs What's up, Doc? carrots→ 08:59, 20 August 2014 (UTC)
 * Presumably you mean not Olaf "Braindead" Hinkley the lead guitarist of Norwegian CyberPunk-Polka fusion band "Real Asset" that disbanded in 1979 but this Hinkley. If you propose a test case to try the contention that every "attempted" murder must in the natural order of things eventually succeed, the defence will likely point to the extenuating circumstance that so-called murder victims are all biochemically pre-programmed to die anyway. Observation of Brain death can lead to a false positive test on a patient that may recover with more time. Zack Dunlap in 2008 had a false positive of this type, likely due to temporary Cerebral edema. Such events feed the fear of being buried alive that has troubled humankind for centuries. Plato wrote in "The Republic" in 380 B.C., about an Armenian soldier who was revived two days after being pronounced dead. Fear turned to frenzy in the 19th century, when wrongful burial inventions were marketed with some success. The Safety coffin was a casket with a bell attached by a piece of string which might be pulled to alert people that the buried person was in fact alive (but it is not true that this is the origin of the phrase "saved by the bell"). However if the internee really is dead, his rest in peace or maybe pieces could be assured by a US patent in 1881 on deterring grave robbers by exploding shells that fit onto a coffin. 84.209.89.214 (talk) 12:00, 20 August 2014 (UTC)
 * And I remember when the exploding whale video was the coolest thing. One slip-up with the arming mechanism and that would be a funeral to remember! Wnt (talk) 12:04, 20 August 2014 (UTC)


 * Although of course it's true, as others have pointed out, that a wound to any part of the body can eventually lead to general system failure which causes brain death, it's also quite possible for an injury directly to the brain to cause brain death after a protracted period -- days, weeks, months, or even years. The main causes of delayed brain death are (1) the initial injury causes swelling of the brain, which gradually crushes other parts, or (2) the initial injury causes an infection inside the brain.  It can also happen that the initial injury causes a blood clot that eventually breaks loose, causing a stroke.  Or you can get a subdural hematoma. Looie496 (talk) 13:59, 20 August 2014 (UTC)


 * According to our article Mortal wound, "A mortal wound is a very severe and serious injury ...... which leads directly to the death of the victim. Death need not be instantaneous, but follows soon after." Based on this, a wound that results in a slow lingering death would not usually be called a "mortal wound".  CBHA (talk) 14:13, 20 August 2014 (UTC)

Question my nephew asked me to pass on
Eight ingots of pure sodium walk into a bar. The juke-box immediately starts playing this music. Why? --Shirt58 (talk) 12:27, 20 August 2014 (UTC)
 * The Batman Theme's lyrics are "nananananananana BATMAN". Na is the atomic symbol for sodium.  -- Jayron  32  12:41, 20 August 2014 (UTC)
 * And as they begin to leave the establishment, someone could play Na Na Hey Hey Goodbye. ←Baseball Bugs What's up, Doc? carrots→ 13:07, 20 August 2014 (UTC)
 * Naa na na nana na naa, nana na naa, Hey Jude ... Gandalf61 (talk) 13:22, 20 August 2014 (UTC)
 * Presumably these songs fall within the genre of Light Metal. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:24, 20 August 2014 (UTC)
 * Wrong answer! That light pop act from the 1980's "BaNaNaRaMA" are by definition an admixture of light and heavy metals. Or something like along those lines.--Shirt58 (talk) 13:56, 20 August 2014 (UTC)
 * Vic Bondi's band opened for them. DMacks (talk) 14:23, 20 August 2014 (UTC)

Plastics oxidation
Did the plastics had been oxidation by water?--Alex Sazonov (talk) 14:01, 20 August 2014 (UTC)
 * There is no common plastic that reacts with water. But see the article on Biodegradable plastic. For example, aliphatic polyesters are biodegradable due to their potentially hydrolysable ester bonds. 84.209.89.214 (talk) 18:27, 20 August 2014 (UTC)
 * Is it the paradox that, the water which is the simple chemical substance is reacted with complex (implex) chemical substances as plastics?--Alex Sazonov (talk) 16:37, 21 August 2014 (UTC)
 * I know that, only simple chemical substances always are reacted with simple chemical substances and only complex (implex) chemical substances always are reacted with complex (implex) chemical substances, is it right?--Alex Sazonov (talk) 17:52, 21 August 2014 (UTC)
 * I know that, a water always had the simple chemical valence.--Alex Sazonov (talk) 19:56, 21 August 2014 (UTC)
 * I know that, the chemical substances which had a simple valence are not reacted with chemical substances which had a complex valence. Valence of chemical substances is identified a statics or dynamics of charge?--Alex Sazonov (talk) 11:09, 22 August 2014 (UTC)


 * There is absolutely no reason why simple and complex molecules (whatever you might choose to mean by these) cannot react. Valence is a property of (oxidation states) of atoms or ions, not of molecules, so I don't understand your last two questions. --ColinFine (talk) 13:45, 22 August 2014 (UTC)
 * Does the properties of charge don’t prevents the chemical reactions between chemical substances which had a complex and simple valence? What does a valence of chemical substances is identifies a statics or dynamics of charge?--Alex Sazonov (talk) 15:29, 22 August 2014 (UTC)
 * Valence (chemistry). 84.209.89.214 (talk) 12:11, 23 August 2014 (UTC)
 * As I learned, the Law of conservation of energy always is right in mathematics, that’s why the mathematical Law of conservation of energy always is observed in chemistry and physics. And also, the properties of charge of chemical substances always are determined the faster time of all chemical reactions and it chemical effective. That’s why I supposed that, in according with the Law of conservation of energy only simple chemical substances always are reacted with simple chemical substances and only complex (implex) chemical substances always are reacted with complex (implex) chemical substances.--Alex Sazonov (talk) 16:48, 23 August 2014 (UTC)

Opera singer vs bulletproof glass
This question was inspired by X-Men: Days of Future Past, in which one character is breaking another character out of a glass-and-plastic prison. I am aware that superhero movies are rarely reliable sources for how real-world physical laws behave, but I'm curious about the general principle behind the first character's method of pulling off the jailbreak: Since in the story his mutant power is the ability to move at very, very high speeds, what he essentially does is press both of his hands to the pane of bulletproof glass separating him from the imprisoned character and vibrate his hands at a high rate of speed. The glass, of course, shatters.

It seems to me that the filmmakers intend for this method to work on the same physical principle by which opera singers are capable (under certain circumstances) of shattering wine glasses. The two main problems I see with this idea are, 1) Unlike wine glasses, bulletproof glass is not hollow and thus does not resonate as much as a wine glass, and 2) Bulletproof glass is... well, bulletproof, at least in theory. It ought to be much harder to break it than your average wine glass using only sound, and the amplitude required to do so would probably be great enough that it would be very hard to contain the damage to the glass alone. While I don't doubt that you could construct a sonic cannon of some kind that could break bulletproof glass, I wonder what difficulties there would be in doing so without destroying just about everything else in the surrounding area, including human (or mutant) eardrums. Evan (talk&#124;contribs) 15:43, 20 August 2014 (UTC)


 * Presumably the destructive power applied by contact is ultrasound. In established Ultrasonic welding of plastics, high frequency low amplitude vibration is used to create heat by way of friction between the materials to be joined. Increasing the sound power to the liquefied plastic could cause Cavitation as employed in ultrasonic cleaning baths, which can erode holes in a metal foil. Crazing (sudden formation of a network of cracks) can be triggered in some glassy polymers, which offers interesting Special effect possibilities in filming. Humans exposed to ultrasound will not necessarily hear the inaudible vibrations, although it is possible to generate audible sound frequencies by mixing of ultrasonic frequencies in body tissue, but they are vulnerable to cavitation damage that may cause nausea, headache, tinnitus, pain, dizziness, and fatigue. See the article Sonic weapon. 84.209.89.214 (talk) 18:10, 20 August 2014 (UTC)


 * Bullet RESISTANT glass is a laminate made up of thick glass panes and/or polycarbonates/laminates. The very design makes it impossible to fully shatter via sound or direct vibrations. Justin15w (talk) 15:40, 21 August 2014 (UTC)


 * Agreed. Only very hard items are subject to shattering due to vibration, because they can't move much.  Sandwiching in softer materials allows them to squish around and absorb vibrations and change them to heat.  So, melting is more likely than shattering.


 * Note that a similar medieval technique was to combine wooden fortress defense walls with layers of sand, which would absorb impacts. (Quartz sand, ironically, is glass, so is quite hard, but the spaces between the grains allow it to move to absorb impacts or vibrations.) StuRat (talk) 16:19, 21 August 2014 (UTC)


 * You should be able to break it in theory. Shattering is another story. I don't know if ultrasonoic is all that destructive, but Quicksilver should presumably find the resonant frequency of the plane of glass, which can be very destructive. --Wirbelwind( ヴィルヴェルヴィント ) 23:42, 21 August 2014 (UTC)


 * Did the movie actually indicate the glass was bulletproof? I don't recall that it did, though I certainly could have missed it.  My impression was that it was simply a thick layer of ordinary glass (which of course could shatter).  Though to be fair, I may have formed that impression simply because Quicksilver shattered the glass and I already knew that bulletproof glass would never break that way.  Dragons flight (talk) 00:47, 22 August 2014 (UTC)


 * If I'm reading correctly, true Bulletproof glass is a combination of different kinds of glass as well as polymers. It's vaguely like a transparent equivalent of plywood. ←Baseball Bugs What's up, Doc? carrots→ 04:05, 22 August 2014 (UTC)

Feral estrildid-like finches-- ID needed
I just saw these odd little birds at a local park; they seem to be some type of estrildid finch, possibly a domestic breed. I assume they are cage escapees because no estrildids are native to my area, though some have been reported (I have recently seen a Zebra Finch myself). Photos are at the bottom of my eBird checklist: http://ebird.org/ebird/view/checklist?subID=S19523282 75.4.19.68 (talk) 16:40, 20 August 2014 (UTC)


 * Are all the photos of the same bird? Anyway, small chance it could be a society finch, they are basically the domesticated version of the zebra finch White-rumped_munia. However, their coloration patterns are highly variable (do some google image searches), so I don't think you could confirm it as a society finches without catching one... Society finch is also a parsimonious answer, as they are commonly kept as pets. While some people do keep e.g. Gouldian_finches or Red-cheeked_cordon-bleu, the Society and Zebra finches are far more common outside their native ranges. SemanticMantis (talk) 22:14, 20 August 2014 (UTC)


 * Those are two different birds, but they looked identical. Society finches look plausible, except I don't see any on Google with orange beaks. I might also note that there have been some odd sightings of orange-cheeked waxbills and bronze mannikins around here, but neither of those seem likely. 75.4.19.68 (talk) 22:24, 20 August 2014 (UTC)
 * Yeah, the orange/red color on the beak made me suspicious too. The only other guess I have is female or juvenile strawberry finch aka Red_avadavat, though again, they have a lot of variation in color, especially on the pet market where many birds are not purely wild type. Actually, come to think of it males probably wouldn't be in full color this time of year, assuming you are in North America. I'm fairly sure society finches can and will breed with other estrildids, especially if if a conspecific mate for the wild type is lacking (they are much easier to breed than wild types, and are often used as living incubators for other species). So, a hybrid (e.g. society and zebra) might be an option too. Looking through Estrildid_finch I only see a handful that I've ever heard of for sale on the pet market (my mom used to breed finches, so I heard a lot about that market...) Of course it might not even be an estrildid, but I agree with you that that's what these unknowns look like, based on size, body shape, and beak shape. That's about all I've got, good luck! SemanticMantis (talk) 00:03, 21 August 2014 (UTC)
 * Juvenile avadavats do seem like the most plausible option I've investigated so far. I have also wondered if their two-tone beaks are in a transitional stage, from juvenile to adult or nonbreeding to breeding. 75.4.19.68 (talk) 00:13, 21 August 2014 (UTC)

OP here: I have talked to a local birder who saw my eBird post, and it seems my birds are not estrildids at all. They are juvenile Pin-tailed Whydahs, which look like estrildids because they are both related to, and brood parasites of, birds in that group. So can I get this marked as resolved? 75.4.24.91 (talk) 18:47, 21 August 2014 (UTC)
 * Interesting! I can't find many good photos of juveniles, but I'm willing to trust the judgement over a local birder over my own armchair guesses :) FYI, you can mark any of your own questions as resolved whenever you like, using the tag, which I will do now below. Cheers, SemanticMantis (talk) 21:27, 21 August 2014 (UTC)