Wikipedia:Reference desk/Archives/Science/2011 July 21

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July 21

Easy-to-understand applications of calculus

I'm looking for example applications of calculus that a middle schooler can understand. The first couple examples I came up with were not very good (they required too much explanation to be understood.) Can someone suggest a few easy-to-understand examples? --71.185.178.173 (talk) 01:47, 21 July 2011 (UTC)

(1) You have 60 feet of fencing and you want to build a rectangular enclosure with the largest possible area -- what should the dimensions be?

(2) You drop a rock from the top of a building and it takes five seconds to hit the ground. How high is the building? Looie496 (talk) 02:07, 21 July 2011 (UTC)

Calculus is the mathematics of change. If you can get that point across, you can probably come up with all sorts of applications. Whereas other forms of mathematics a middle schooler is familiar with are primarily mathematics of being (that is, they allow you to describe static systems), calculus allows you to mathematically calculate what happens in systems where everything is changing. Differnetial calculus is useful for calculating instantaneous change in a complicated system. Instantaneous change is pretty easy for a kid to understand. If you drive a car for 60 miles and it takes 2 hours to get where you are going, that's an "average rate of speed" of 30 miles per hour. However, when you look at the speedometer at any point on your trip, you don't see 30 miles per hour the whole time. What you see sometimes is 40 or 50 miles per hour; other times you are stopped completely. The speed at any given instant is the "instantaneous rate", and differential calculus is about calculating that instantaneous rate for any complex system. Integral calculus is about the effects of cumulative changes; that is looking at how a dynamic (or constantly changing) system accumulates change over time. So, if I am trying to see how much gas my car uses, ultimately that ends up being an integral problem, because it is always using gas, and over time I just keep using more and more of it. For any complex system where I want to know what cumulative effects of all of the little changes along the way are, integration is the way to go. --Jayron32 02:50, 21 July 2011 (UTC)

Uuh, you don't need calculus to solve Looie's second problem. Clarityfiend (talk) 03:49, 21 July 2011 (UTC)

You do to solve it starting from $F=ma$, with the assumption that gravity generates a constant force. (Well, strictly speaking there are alternative ways, but they are much more complicated.) Looie496 (talk) 04:05, 21 July 2011 (UTC)

You don't need calculus to solve either of Looie496's example problems! the first can be solved with analytic geometry, and the second with kinematics. But, the solutions are easier and more flexible in both cases if you use a calculus approach. This is true of most simple calculus applications; a more elaborate treatment using simpler concepts exists; but if you take the time to learn the more complex concepts of calculus, the solutions are simpler to compute. Nimur (talk) 06:37, 21 July 2011 (UTC)

All I'm saying is that the second question (as stated) is too simple. You can easily figure out the rock's speed after five seconds and use that to calculate the total distance traveled, all with nothing more than arithmetic. Why risk confusing a middle schooler by telling him/her to attack a problem by a much more involved method when a simpler, more intuitive one works fine. It makes sense to use Jayron's car example instead. Clarityfiend (talk) 08:19, 21 July 2011 (UTC)

Strictly speaking, you don't need calculus to solve any problem; it's just such a handy, general framework for solving certain classes of problems that it might as well be indispensable. If one understands the calculus-based approach to Question 2 (and how integration can take you from a force – and corresponding acceleration – to a velocity, to a displacement) then one can start to incorporate additional physical principles, like drag (as a function of velocity, or even as a function of both velocity and altitude). Consider a parachutist instead of a rock for a bit more intuitive relevance. In a similar vein, one might look at a rocket that produces constant thrust, but is burning fuel (and so loses mass with time). That one's pretty easy, but a pain in the neck to do by anything but calculus. TenOfAllTrades(talk) 12:55, 21 July 2011 (UTC)

You would need to know the terminal velocity of your rock though if you wanted a real world solution rather then a highschool textbook solution. Googlemeister (talk) 12:58, 21 July 2011 (UTC)

I mentioned the dropped-rock problem because I have used it myself when teaching calculus to a university class, and found it to work very well -- it actually engaged the class more than any other problem I showed them. I think part of the reason it interested them is that I could say that I had actually used the method to estimate the height of a cliff I was standing on top of. Looie496 (talk) 17:31, 21 July 2011 (UTC)

I think Zeno's paradox is a nice example of something that needs calculus to solve. --Stephan Schulz (talk) 11:42, 21 July 2011 (UTC)

Length-of-curve and area-of-surface for mathematical shapes are some possible practical applications. "How much wire to connect two poles a certain distance apart?" "How much cardboard to make a megaphone of a certain length and cone-angle?" "How much silver for a parabolic reflector?" etc. Each could be reduced to a specific equation for a particular shape and perhaps certain restrictions on dimensions, but those are all just specific results "in each of these cases, use this separate simplified solution" of the general calculus (single approach vs different analytical-geometry for each?). DMacks (talk) 14:40, 21 July 2011 (UTC)

Calculus is needed to compute almost anything, even in problems that seemingly don't require any calculus at all. E.g. if you do some primary school level geometry problem and you find that some ratio is given by sin(10°) = 0.173648... then this involves calculus. This is hidden from you because your calculator computed the numerical approximation for you.

A lot of what is considered to be "pre-calculus" strictly speaking isn't. The moment you need to evaluate a logarithm, some trigonometric function, some square root etc. etc., you are already doing calculus. Even using a calculator to perform a division can involve calculus, because your calculator does not use long division to compute the answer, it uses more advanced algorithms that are typically based on calculus. Count Iblis (talk) 14:53, 21 July 2011 (UTC)

A simple example is radioactive decay. If you count the decays of a long-lived isotope you could extrapolate linearly and come to the conclusion that there will be no material left after a certain time (the multiplicative inverse of this time is called the decay constant). Use calculus to show that the fraction of the original material still left after this time span is in fact the multiplicative inverse of e. You don't need calculus in order to see that there is an exponential law, but you probably need it in order to compute half-lives from decay constants. Icek (talk) 21:32, 22 July 2011 (UTC)

Calculus is just a "discovery" that aids in many math problems. Try this rather famous example template: A frisbee disk is thrown in a straight line on a diagonal, and a dog must run in a hyperbolic path to reach it in the shortest time while constantly running toward the disk. Calculate the total distance formed by the path. ~AH1 ^(discuss!) 16:46, 25 July 2011 (UTC)

need help

My dad is suffering from ckd stage 5 we wish to have a artificial kidney transplant we need some details where it happens and the procedure if you can provide some info it will be of great help looking forward to here from you soon — Preceding unsigned comment added by 106.77.63.81 (talk • contribs)

The Wikipedia Reference Desks may not provide you with any medical advice. However, in terms of general information, our article on artificial kidneys says that the only artificial kideny technology currently available is hemodialysis, and that "currently, no viable bioengineered kidneys exist". Gandalf61 (talk) 08:32, 21 July 2011 (UTC)

If you used "artificial" inadvertently, you might want to read our article kidney transplantation, which is about the forms of renal transplants actually available at the present time. - Nunh-huh 18:41, 22 July 2011 (UTC)

Shuttle deviated from planned track?

[1] This is a screen capture from just a moment ago on NASA TV of STS-135 landing. Did the shuttle left its planned track? Why? thanks 122.61.218.145 (talk) 10:10, 21 July 2011 (UTC)

We need more information about that diagram to be able to interpret it. It made a perfect landing according to BBC News. The diagram presumably shows in-flight adjustments.--Shantavira|^{feed me} 12:26, 21 July 2011 (UTC)

The objective of the guidance and navigation systems is to arrive at a certain place (the heading alignment cone, which is the circle you see at the end of the green line) with a certain amount of energy (airspeed and altitude). The objective is not to follow the predicted path exactly; in fact the navigation system probably doesn't know it's off the green line. It knows where it is, where it should go, and computes how to get there. The green line is only an estimate on how the guidance and navigation will steer the vehicle and is limited by the knowledge of atmospheric density, winds, and a host of other factors which can't be known precisely. The yellow line and red triangles show how the actual vehicle responded to the actual conditions. The deviation from predictions is not a big deal so long as the shuttle arrives at the right place (the HAC) with the right airspeed and altitude, so the next phase of guidance can point it right to the runway. anonymous6494 15:50, 22 July 2011 (UTC)

Very helpful, thanks. 122.61.218.145 (talk) 12:06, 24 July 2011 (UTC)

world map in future

I want to know (roughly) what will the world map be like around 20 million years.Please!! thanks in advance.--Irrational number (talk) 10:41, 21 July 2011 (UTC)

This NASA article has projections at 50 million years and 250 million (Pangaea Ultima) projected by Christopher Scotese. An animation showing now->250 is here. At only 20 million it's quite similar to the current map. -- Finlay McWalter ☻ Talk 10:56, 21 July 2011 (UTC)

Of course, this is all highly speculative. We still don't know enough about mantle dynamics and plate tectonicss to make an accurate prediction beyond "Stuff's going to keep moving the way it's been moving". -RunningOnBrains^(talk) 13:01, 21 July 2011 (UTC)

The prediction for +20 million years is not very speculative -- even the fastest continents can only move a few hundred miles in that time. The main exception is the southwest Pacific, which has the fastest motions and a very complex plate topography. Other than there, simply extrapolating the current motions ought to give a pretty good prediction. It's only beyond the 50 million year mark that the extrapolations start to become dubious. Looie496 (talk) 17:22, 21 July 2011 (UTC)

India was an exception, estimated at 18-20cm/yr for some time, maybe ~4000km in 20ma. Impressive. Sean.hoyland - talk 17:59, 21 July 2011 (UTC)

Regarding the NASA popular article, wouldn't there be a new sea in place of Africa's Great Rift Valley? Icek (talk) 21:14, 22 July 2011 (UTC)

You could, of course, make your own simulation by shifting around paper models of plates on a sphere...or something. ~AH1 ^(discuss!) 16:41, 25 July 2011 (UTC)

FTL

I read the articles about faster-than-light traveling wormholes and alcubierre drine. my conclusion was that FTL traveling is either impossible or not practical (and I was very disapointed,by the way) is my conclusion correct?

my other question is that are speeds like 0.5c efficient for traveling inside the galaxy?thanks in advance--Irrational number (talk) 10:50, 21 July 2011 (UTC)

Well that depends on what you mean by efficient. At .5c, the nearest star to us is a 9 year journey. I would not be that interested in a 9 year one way trip, but others might be. The trick is to be able to supply all water, food, oxygen and medical treatment for a group of people (sending just 1 would be a bad idea because people don't usually do too well with that kind of isolation for a long duration). Googlemeister (talk) 12:55, 21 July 2011 (UTC)

1. (edit conflict)According to the laws of physics as they are known today, FTL travel is impossible.
2. It depends on where you want to go in the Galaxy. The Milky Way is 100,000 light years across, so if you want to get to the other side, you're SOL. I don't have time to do calculations right now, but I suspect at 0.5c you're still going to need years to get beyond the closest few stars. In principle the technology exists for humans to at least visit our local neighborhood of stars within a couple decades; see Project Orion. But unfortunately we're not going to be visiting the center of our galaxy any time soon.-RunningOnBrains^(talk) 12:58, 21 July 2011 (UTC)

Also bear in mind that the faster you travel, the slower you move through time, so at high enough speeds, what might seem like a years-long journey to those stuck on earth could be just a couple weeks to those in the spaceship. --Goodbye Galaxy (talk) 13:36, 21 July 2011 (UTC)

What is the formula for that? If you travel at 50% of light speed, does time move half as fast? --George100 (talk) 14:27, 21 July 2011 (UTC)

No. I believe the formula is $\gamma ={\frac {1}{\sqrt {1-{\frac {v^{2}}{c^{2}}}}}}$. So if my math is right, a 4 lightyear trip at .5 c would appear to take approximately 6.95 years for those aboard the spaceship (instead of 8 years for everyone on Earth). It's not until you get much closer to the speed of light that time dilation really starts to ramp up. --Goodbye Galaxy (talk) 14:41, 21 July 2011 (UTC)

Here is the article about this formula. It is a version of the Lorentz contraction. --Mr.98 (talk) 14:48, 21 July 2011 (UTC)

Okay, now I'm confused. It's been a few years since I took relativity, so bear with me. I know there are two effects at play when you talk about interstellar travel at relativistic speeds: time dilation and length contraction. So at 0.5c, does that mean that the distance to Proxima Centauri is only 3.6 light years instead of 4.2 light years? And so then your time of travel would be 7.2 years to that star? -RunningOnBrains^(talk) 14:58, 21 July 2011 (UTC)

It would be nice if someone would start an article on roddenberry (unit) and make up a pretty conversion table. In theory I could do it, but I never seem to... Wnt (talk) 14:58, 21 July 2011 (UTC)

Yes, I believe you have it right, Runningonbrains. --Goodbye Galaxy (talk) 15:06, 21 July 2011 (UTC)

It's true that for someone on the ship the trip only takes 7.2 years. You can attribute this either to time dilation (their sense of time is slower than the Earth people's), or you can attribute this to length contraction (the sun and Proxima Centauri are both moving at 0.5c relative to the ship, but they pass by in only 7.2 years to the people on the ship so their distance in this frame must be only 3.6 ly). Rckrone (talk) 15:23, 21 July 2011 (UTC)

A photon rocket that uses anti-matter as fuel would be pretty efficient for travelling very close to the speed of light. If the initial mass of the rocket is $M_{1}$ and the final mass is $M_{2}$, then the gamma factor that is reached is given by:

$\gamma ={\frac {1}{2}}\left({\frac {M_{1}}{M_{2}}}+{\frac {M_{2}}{M_{1}}}\right)$

If you want to travel some distance and then stop, the same mass ratio is needed again (because after stopping, you would be moving at the same gamma factor relative to the previous co-moving frame), so the gamma factor you can travel at, given some amount of anti-matter fuel on board is then given as:

$\gamma ={\frac {1}{2}}\left({\sqrt {\frac {M_{1}}{M_{2}}}}+{\sqrt {\frac {M_{2}}{M_{1}}}}\right)$

Count Iblis (talk) 15:12, 21 July 2011 (UTC)

animal classification

I wanted to have some information about animal classification in order to understand evolution (by observing similarities between several species).The wikipedia articles are a bit too advanced for me, and I found this helpful, but a bit short because it's mostly about human.do you know any better place? thanks.--Irrational number (talk) 11:04, 21 July 2011 (UTC)

Well, we can help if you have specific questions about taxonomy or taxa. The 'observing similarities between species' idea is loosely the business of phenetics, while the more modern approach to taxonomy is based on cladistics. I don't have any good external references, but you may enjoy the 'simple English' versions of some of these pages, such as evolution here: [2]. SemanticMantis (talk) 14:24, 21 July 2011 (UTC)

To put it in simple terms; using physical characteristics can be confused by issues such as convergent evolution; it would be like claiming that bats, birds, and butterflies we closely related merely because they shared the ability of flight. Cladistics means developing a taxonomic system based on common ancestry, and to think in terms of going forward in time, rather than backwards. Thus, a clade can be thought of as all of the decendents of a common ancestor. Some of our common classifications of animals are cladistic, and some are not. For example, the entire group of primates are a clade; in that all primates share the same common ancestor, and that ancestor's complete set of decendents are the primates (that is, there aren't a group of non-primate animals that are decended from that common ancestor). The group of animals we call monkeys, however, are not a clade because they do not share a single common ancestor that whose decendents includes only monkeys. The group of animals we call "reptiles" are also not a clade, but for a slightly different reason: the common ancestor of all reptiles has decendents (birds and mammals) which are not considered to be reptiles, thus the traditional classification of reptiles doesn't represent a clade. The clade that contains reptiles would also contain mammals and birds, since the common ancestor of all reptiles can also count birds and mammals as its decendents. --Jayron32 18:07, 21 July 2011 (UTC)

Just to add some terminology to Jayron's nice explanation, these concepts are discussed in more detail at monophyly, polyphyly, and paraphyly. SemanticMantis (talk) 18:25, 21 July 2011 (UTC)

Dishwasher magnets for softer water

Norwex (one of those innumerable semi-pyramid home-selling things) is offering an item they call a magnet ball (this has more details). The blurb says "The Norwex Magnet Ball is a money-saving device that removes calcium molecules from the water by magnetically attracting them to the inside of the ball. This action makes the water behave as though it was "soft"." I'm not a scientist (liberal arts major!), but I just don't see how this could possibly work. Reviews like this don't give me a warm feeling either: "There's no way this could work" vs. "My customers love them!" So, science-types, what's the skinny here? Matt Deres (talk) 11:28, 21 July 2011 (UTC)

It's a scam. If you are concerned about your laundry, simply knocking on wood before starting the machine is twice as effective, at a much lower price. --Stephan Schulz (talk) 11:44, 21 July 2011 (UTC)

A laundry ball by another name I think.--Shantavira|^{feed me} 12:29, 21 July 2011 (UTC)

I agree. It is a scam. The claim that it "removes calcium molecules from the water by magnetically attracting them to the inside of the ball" is total, complete bullshit. 148.177.1.212 (talk) 12:36, 21 July 2011 (UTC)

Is calcium even magnetic? This product seems absurd. Googlemeister (talk) 12:51, 21 July 2011 (UTC)

No, calcium is not magnetic. The claims are intentionally deceptive. ChemNerd (talk) 12:56, 21 July 2011 (UTC)

Calcium (the Alkaline earth metal in elementary form) is slightly diamagnetic, meaning the magnets in the ball would repulse it. Of course, "slightly diamagnetic" is scientist lingo for "really really not magnetic in the everyday sense of the word". Moreover, metallic calcium reacts fairly violently with water. The "calcium" making water "hard" is mostly calcium carbonate (or calcium bicarbonate), and I have no idea if individual Ca²⁺ ions in aqueous solution have a significant magnetic moment. --Stephan Schulz (talk) 13:06, 21 July 2011 (UTC)

Calcium ions are diamagnietic, but then again, so is water. -RunningOnBrains^(talk) 13:12, 21 July 2011 (UTC)

It's not cheap either. How do these people get away with it? These things have been around for some years now. Aren't there laws against this sort of thing?--Shantavira|^{feed me} 13:01, 21 July 2011 (UTC)

We have a magnetic water treatment article, which seems applicable. It calls such devices "ineffective and pseudoscientific." -- Finlay McWalter ☻ Talk 15:19, 21 July 2011 (UTC)

There are certain key words which are redflags for bullshit products that are outright lying to you about what they claim to be able to do. Magnets, ions, and toxins are three which almost always mean what they are selling you doesn't do anything. --Jayron32 17:55, 21 July 2011 (UTC)

I'd say the placebo effect has a role in this as well. Say someone, Mrs X, falls for the ad, gets her calcium ball thing and uses it. Now, by sheer virtue that the water is supposed to be softer and the clothes are supposed to be cleaner, she will be convinced of the fact that it really is so because her brain will more or less tell her that it is supposed to be like that. She speaks to Mrs Y, who has a lot of problems with her hard water, and Mr Z, that insecure retired shopkeeper who is always looking to protect himself from toxins, and they get their balls as well... and so on... now, for those two other people, the advertisement will probably play no role because they've been offered hard proof (i. e. Mrs' X conviction that the thing actually works wonders) - they're been offered facts. --Ouro (blah blah) 07:35, 22 July 2011 (UTC)

I don't know why I was thinking about clothes... --Ouro (blah blah) 13:57, 22 July 2011 (UTC)

I think the elephant in the room with the blue laundry balls is that to some degree all laundry soap is a placebo. We have a tradition of clothes-washing that dates from the days when the streets were mudded ruts full of horse poop and chamber pots tossed out windows, when buildings were blackened with soot from unregulated air pollution. Machine washing gets better and better, but all people are trying to lose is the smell of sweat and maybe a few drops of butter. So you can throw in your clothes, leave out the detergent, toss in an imaginary blue laundry ball, and be perfectly satisfied with the results, much of the time. I think in this case the scam is simply being extended to a new field, but the idea is similar: a fancy modern dishwasher using hot water can simply physically remove most of the trouble anyway. Obviously this scam makes money, so people will keep doing it and adapting it further. Wnt (talk) 18:09, 22 July 2011 (UTC)

. Having forgotten to add laundry detergent to many a load, I can say that it certainly removes odors; the converse (washing stinky laundry without the soap) has a certain bouquet which is instantly recognizable as "crap, I forgot to add the laundry soap again". You can decide whether or not such odors represent a real problem or not, but I don't like them, so I will continue to use soap to get them out. --Jayron32 19:29, 22 July 2011 (UTC)

ISS Airlock Spec

Are detailed specifications of the International Space Station's airlock freely available, or do only well-moneyed companies like SpaceX that would really be able to do something with them have access? You don't need to tell me "See Quest Joint Airlock." I see the section entitled Airlock Specifications, but I'd like to just look at engineering drawings. 20.137.18.50 (talk) 14:25, 21 July 2011 (UTC)

I found it myself. For anyone else curious, it's here. 20.137.18.50 (talk) 16:33, 21 July 2011 (UTC)

I'm slightly confused by your question. That last thing you've linked to is IDSS, which is an international ISS spec based on the US International Low Impact Docking System, a spacecraft docking and berthing mechanism. Quest isn't for docking; it's an EVA airlock. I don't see why any vehicle would need to be compatible with Quest, as it's permanently mated to ISS. -- Finlay McWalter ☻ Talk 16:57, 21 July 2011 (UTC)

When I said airlock, in my mind I was only thinking about the docking, meaning the point of connection between two spacecraft. I was apparently wrong to reference Quest then. What part of the ISS "joined lips" with the Space Shuttle? 20.137.18.50 (talk) 17:02, 21 July 2011 (UTC)

TO an APAS-95 on one of the three Pressurized Mating Adapters. -- Finlay McWalter ☻ Talk 17:08, 21 July 2011 (UTC)

Venom

How come humans never evolved venom glands in there body as a defensive feature. — Preceding unsigned comment added by 109.76.37.33 (talk) 20:14, 21 July 2011 (UTC)

Evolution does not create something just because it might be cool. Evolution is not intelligent. Evolution is merely the result of which sperm and eggs were used to create the next generation. There hasn't been a trend to prefer to breed with humans who have anything similar to venom glands. -- kainaw™ 20:16, 21 July 2011 (UTC)

See also venomous mammals. There are very few. SemanticMantis (talk) 21:37, 21 July 2011 (UTC)

Every feature an organism has increases the amount of food it needs to eat, since every feature will consume energy (even if just to maintain the cells it is made up of). That means that the benefit of the feature needs to be greater than the cost of the extra food requirement (all in terms of reproductive success). It may well be that venom glands wouldn't meet that threshold. There is also the issue that evolution is a gradual process. If half a venom gland is not more use than no venom gland at all, venom glands won't evolve. The way evolution tends to get around that problem is by converting existing organs to serve new purposes (eg. snake venom is made by modified saliva glands), but even that requires useful intermediary steps (Evolution suggests the venom originally helped digest food, but that is yet to be determined with any certainty). So, as you can see, new features don't just appear. Conditions need to be just right. --Tango (talk) 21:42, 21 July 2011 (UTC)

Actually, I'm not sure that humans aren't venomous, or at least poisonous, in a broad sense. For example, in conflict with other primates, we know that Herpes B virus, carried with few symptoms by monkeys, is lethal to humans - I'm not sure humans don't carry some strain of cold sore that would be lethal to other primates. Like certain types of sharks, humans have high levels of uric acid in their tissues; I'm not sure how edible the meat really is - certainly there are enough predators that seem to avoid it. In the modern world, we try to reduce the level of predation on humans to such a low level that we really don't know that much about it. Wnt (talk) 22:07, 21 July 2011 (UTC)

Humans are extremely poor at up-close fighting. Not only did we not evolve venom glands, we've also got essentially no fangs, no claws, very soft skin, and very weak muscles.

In exchange we've got endurance, fine precision motor skills, opposed thumbs, and, of course, superior intelligence and the ability to learn languages easily. (At least when we're young.)

So, I don't think venom glands are in our near future. Right now we seem to be headed in the other direction. We've been given the ability to build weapons so we don't need to use our teeth to fight, and the ability to build cities so we don't need to fight other animals in the first place. Not as bad-ass as venom glands, I'll admit, but much more useful. APL (talk) 05:22, 22 July 2011 (UTC)

Who needs venom glands when you can have a CS gas grenade? Googlemeister (talk) 12:56, 22 July 2011 (UTC)

Do breeding GBB gulls utilize 'helpers'?

Yesterday, I had the chance to observe a breeding pair of Great Black-backed Gulls and their recently-fledged chick. The baby gull was walking back and forth between the birds which were obviously its parents, crying to be fed and pecking at the 'red spot' on mum and dad's beak (as they do) and it appeared as though the parents were mostly trying to ignore it, to encourage it to fly around and start finding its own food (as they do). However, there was also a third adult Great Black-backed Gull in the vicinity, the presence of which seemed to be tolerated by the breeding pair (which is unusual) and in turn, it tolerated the chick, which seemed to have decided to try begging food from another gull after having no luck with its parents, to approach and peck at its 'red spot', (again, this is unusual - it would be typical for an adult gull to peck at and chase away any unrelated chick that approached it). This got me thinking - are gulls ever known to use helpers at the nest? I've never heard of it before - but it would certainly be one explanation for the behaviour I witnessed, say if the third adult was the offspring of the pair. As far as I'm aware, there has been a pair of GBB gulls nesting in this location for several years now - and it is certainly possible that they are the same birds (gulls being long-lived, mostly-monogamous and definite creatures of habit), now old enough now to have fully-grown offspring. Any thoughts? --Kurt Shaped Box (talk) 23:25, 21 July 2011 (UTC)

Wait, aren't you the gull expert here? --Jayron32 01:18, 22 July 2011 (UTC)

Well, I know enough about gulls to know that the behaviour I described in my OP isn't typical of this species of dinosaur... --Kurt Shaped Box (talk) 01:49, 22 July 2011 (UTC)

I spent a few minutes searching, and found no record in the scientific literature... Keep in mind that birds of *many* species will beg food from anything remotely parent-like (and the other male may well respond aggressively next time). On the other hand, lack of published data doesn't mean it doesn't happen. Let us know if you see the young bird feeding from three different adults! SemanticMantis (talk) 12:49, 22 July 2011 (UTC)