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The world I'm building is similar to medieval Europe but with magic and dragons. Instead of riding horses knights ride dragons. I wonder if it possible for a medieval country the size of England to provide for five hundred dragon knights with only limited help from magic.

Note that the average dragon should be the size of Drogon from Game of Thrones.

Magic is used to heal any wound or sickness that can kill any cattle and sheep or make them infertile. So cattle and sheep only die of old age and should all continue breeding till death. However, magic is not used to make them breed any faster than normal.

Drogon's size: wingspan 48-60 yards or 44-55 meters. His body is 40 feet long. 87,500 pounds.

Dragons can hibernate but must awaken for one full day every two weeks both to feed and to exercise so as to maintain muscle mass.

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  • $\begingroup$ I'm not an expert in got, but especially in the generally very sloppy 2nd to last episode those beasts changed their size within a couple of frames. Since i suspect more people are not experts, would you be so kind to provide us with the official got Dragon weight? $\endgroup$ – Raditz_35 Oct 20 '17 at 15:47
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    $\begingroup$ Glad to see you stated limits of your magic precisely. $\endgroup$ – Mołot Oct 20 '17 at 16:15
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    $\begingroup$ For reference a large carnivore we all know is Tyrannosaurus Rex. A T-Rex is much smaller than your dragons and (as always) xkcd.com helps us visualize T-Rex's dietary needs. $\endgroup$ – StephenG Oct 20 '17 at 16:37
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    $\begingroup$ Bryan, it's kind of bad manners to change the question after answers start rolling in, thus rendering some of them no longer applicable. The best thing to do is to think about these details ahead of time, and then only add clarifying details if requested by the community. The new details regarding hibernation impact my answer, for example, and I may end up getting down-votes, etc. if people think that I've gone off topic, or am not being helpful. If you want to bounce ideas off of the community, join the chat, or the question sand-box, and flesh out the basic concepts there. $\endgroup$ – AndreiROM Oct 20 '17 at 16:39
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    $\begingroup$ Remember that, even if they can't provide for the dragon, a modern biosphere can't naturally support dragons anyway, so 100% diet coverage wouldn't be strictly necessary. The humans have most of the leverage here. $\endgroup$ – user70585 Oct 20 '17 at 22:12
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It looks like no, not if they are carnivores, but it is possible if they are omnivores

There is a nice helpful calculator for this.

So if your dragons metabolism is comparable to a dinosaur or mammal you are looking at roughly about 1,039,878 kilocalories a day, per dragon.

With 975 kilocalories for a pound of beef, that is ~1067 lbs of beef, or roughly
1,778 lbs of cow (only about 3/5th of a cow's weight is "food" aka not bone or skin).

A medieval cow weighed about 75% of a modern cow and a modern cow weighs on average 1,390lbs (so medieval would be 1,045lbs). So that is roughly 2 cows per day per beast or 730 cows per year per beast.

Now what does this mean for your kingdom

It takes 1.5 to 2 acres to feed a cow/calf pair for 12 months and takes about 2 years to raise a cow to slaughtering age, **so to feed your beasts for 1 year, you need 1460 acres of pasture That is roughly 1 large barony (of half one on the small estimate) just devoted to feeding one animal.

For 500 dragons we are looking at 730,000 acres)

Now England contained roughly 43 million acres of farmland today, so it is indeed possible, but you would be looking at 1.6% of the total farm land, and that is modern farmland, BUT a lot less would have been farmable during medieval times, medieval england only had approximately 8,000,000 acres of farmland (according to the domesday survey) that would mean you are using 9% of your total farmland. This is where the estimate gets a bit sketchy pastureland is not the same as farmland but at the same time the medieval farming systems were only capable of utilizing about half the farm land at any given time. Either way thats a huge amount of food, probably more than they could spare. (estimates are medieval communities could only spare about 2% of their food production for the military.

Conclusion So in the end you might well be be starving your farmers to feed the dragons. At the very least would have very little else including no other military or aristocracy, which means their country would very quickly fall apart because it can't feed it's own government.

EDIT alternatively if you go with Will's idea and say they are herbivores (or omnivores) you are looking at only ~200,000 acres to feed all of them, that much more reasonable, double the acreage and say they get some meat/fish with each meal and you have something with a noticeable impact on the kingdom but not a prohibitive one.

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  • $\begingroup$ Can you please clarify how you obtained those Calorie requirements? Using the highest metabolism rate on the calculator site you provided (38.3), I get only 1.5 million Calories, rather than the 9.7 million Calories you list for a dinosaur. Using my own calculations (an average caloric intake of half a dozen different animal species) yields an even lower number for the given body mass. (Note that the Kleiber Law requires body mass in kg, not pounds.) $\endgroup$ – MikeB Jan 25 '18 at 5:07
  • $\begingroup$ yes I put it in pounds not kilograms that is my bad, I will try recalculating $\endgroup$ – John Jan 25 '18 at 7:15
  • $\begingroup$ 9% nothing! I'd think England would simply invade neighbouring countries taking their land and enslave the populace, forcing them to produce food for their dragons! $\endgroup$ – colmde Jan 25 '18 at 17:18
  • $\begingroup$ except invasion rarely result in high net returns. And how exactly do they invade and hold without an army? $\endgroup$ – John Jan 25 '18 at 17:24
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It all depends on how "realistic" you want to make your dragons. Quite frankly, reality takes a back seat when discussing this topic, because flying, fire-breathing beasts that large are not actually feasible.

The amount of food that a large specimen would need to consume to survive, let alone engage in strenuous physical activity such as almost daily training, etc. would be insane, and I seriously question the ability of a medieval nation to keep up with the requirements.

However, since these are magical beasts, there's no reason why they shouldn't be able to subsist on magic itself.

I would probably make it such that dragons love meat, and are consummate carnivores, with the caveat that eating even a whole cow does not provide nearly the amount of energy that dragons require. Which is why traditionally, dragons spend decades hibernating, emerging only to gorge, and then retreating back to their dens.

Dens which they take great pains to stock with magical items they pillage from their hapless victims. They then slowly leach the magical energy from those items over time, thus surviving for decades without having to venture out to hunt.

The very first dragon knights realized that the large piles of gold and gems that dragons are found resting on are not valuable to the beast in and of themselves, but were once a critical source of magical energy! Armed with this knowledge they eventually tamed the first beasts.

The way that modern dragon fleets are maintained, is by having mages enchant dragon pens/harnesses etc. such that the dangerous beasts have a steady source of "food" available, thus remaining awake, and cooperative.

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    $\begingroup$ Great Answer! +1 : So leaving an evil relic in the possession of a dragon is a great way to eventually destroy it AND simultaneously keep it safe from evil people who would want to use it. I am definitely stealing this idea! Awesome! $\endgroup$ – Henry Taylor Oct 20 '17 at 16:48
  • $\begingroup$ @henrytaylor - imitation is the sincerest form of flattery! $\endgroup$ – AndreiROM Oct 20 '17 at 17:13
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    $\begingroup$ @HenryTaylor That is a good idea until you notice that dragons are what they eat. Book 1: How we saved and hid the evil artifact. Book 2: How we have slain the guardian dragon. Book 3: How we accidentally left the magical remains near the stables. $\endgroup$ – J_F_B_M Oct 21 '17 at 9:21
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    $\begingroup$ LOL @J_F_B_M, but I'll be using the dragon as a concealed narrator, telling a story to the reader, who lives in our post-magical age. As the story evolves, the heroes defeat the evil mage, leaving the now neutral artifact with the dragon to guard. Then in the denouement, have the dragon reveal itself, explaining that it eats magic so the artifact has kept it fed for many eons; allowing it to guard the now-magic-less kingdom without need for live-sacrifices. Then reveal a diminished artifact, showing that the free ride (or the dragon's life) is nearly over. No need for books 2 or 3... yet! $\endgroup$ – Henry Taylor Oct 21 '17 at 9:56
  • $\begingroup$ What do you mean dragons aren't feasible in real life? :P worldbuilding.stackexchange.com/questions/313/… $\endgroup$ – DonyorM Oct 22 '17 at 7:59
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This dragon is huge! A WW2 B29 super fortress only had a 43m wingspan. Of course any flying animal of that scale would be impossible in our world, but since you are using magic I think we can let that pass. If you still want to do some sort of realistic-ish calculation without resorting to magic feeding as well as magic lifting, then you need to know the weight of the beast.

Taking a flying fox as a model – not that accurate but this is a rough calculation to say the least and the data is available.

1m wing span and 1kg in mass and assuming an average density of 1kg/litre of animal.

As volume increases with the square of size a creature 50x the size would weigh in at 50 cubed ~125 tons (166tons for a big one)

Animal food requirements very roughly (from here) say 10,000kJ / 100kg / day so a 125,000kg animal would need 1250 x 10,000 kJ / day = 12,500,000 kJ /day

At 7570 kJ /Kg (for beef) so 12,500,000/7570 = roughly 1.6 tons of beef per dragon per day.

At 400 Kg per cow (assuming lighter weight cows from years gone by) that’s 4 cows per dragon per day.

For a …flock? Of 500 dragons that’s 2000 cows per day. I don’t think its manageable.

Solutions – use magic, have fewer dragons, have smaller dragons, keep the dragons resting for a large part of the time so minimising energy expenditure might cut the requirement by a lot x0.25 perhaps? Breed larger cows like today – maybe 1000Kg could be doable, use extensive ranching on a huge scale.

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    $\begingroup$ This answer makes a number of assumptions (namely that the numbers scale proportionally, which is not always true) but I'm going to give it a pass as "being within a power of 10" which is close enough. i.e. even at 0.4 cows per day, that's a lot of cow (146 per year per dragon, meaning your herd size needs to calf that many every year, meaning you need 146 sows just to replace the animals being consumed--and each cow needs ~2 acres of grass to feed itself). $\endgroup$ – Draco18s Oct 20 '17 at 18:05
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    $\begingroup$ Yes fair comment, although given the circumstances I think an order of magnitude estimate is not bad. I assume that these dragons are not the fire breathing variety...that could burn up a few extra calories ;o) $\endgroup$ – Slarty Oct 20 '17 at 18:10
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    $\begingroup$ Food requirements increase at (3/4) power compared to mass. This is known as Kleiber's law. $\endgroup$ – corsiKa Oct 20 '17 at 21:22
  • $\begingroup$ "For a …flock? Of 500 dragons that’s 2000 cows per day. I don’t think its manageable." - Currently, cows are slaughtered at roughly 18 months' age. That means you'd need a total running livestock count of 2000 * 31 * 18 ~= 1.1 million cows. In modern UK, there are about 10 million beef cows. So I'd say on the face of it this sounds feasible, if taxing. The logistics involved in a medieval country would be... interesting. $\endgroup$ – marcelm Oct 21 '17 at 19:43
  • $\begingroup$ @marcelm unmanageable is my way of saying interesting ;o) $\endgroup$ – Slarty Oct 22 '17 at 10:04
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If dragons existed naturally, then their food supply also existed naturally. I think you have to go through the entire chain before wondering whether humans could support them.

How did they live before the humans tamed them? If they lived in this world, save for dragons and magic, then they must have necessarily lived far apart, and spent several hours a day eating small meals over a vast territory. Otherwise they would essentially strip the land of animals and have to move on.

But if they lived far apart and had a huge range (so as not to outstrip their food source) then they didn't reproduce very frequently. Which means they can't adapt. But this then raises the question of how the evolved into such large creatures and survived anyway - what's the evolutionary advantage to a creature that reproduces infrequently, takes up a huge amount of space, and eats vastly more food than any other creature? Typically in evolutionary systems you'd find carnivores are physically smaller (though more powerful) than the herbivores they eat.

I'd suppose that instead there were other very large herbivores in the world that had a high enough reproduction rate and a high enough mass gain rate that they could supply the needs of the dragons. But then either they died off or they are still around. If they died off, then the dragons had to change strategy quickly to survive (ie, had to be somewhat intelligent) as a species because there's no food source to replace theirs with. Perhaps they became more territorial, and then started reproducing less frequently (due to territory issues and finding a mate requires leaving one's territory).

Otherwise the huge herbivores must still be around. They must reproduce frequently, grow quickly, and consume tons of grass daily.

So if you don't want to magically feed your dragons, your best bet is to invent their food source as well - huge cows.

The only remaining issue, then, is that there's not enough land in the UK to grow enough grass to feed the herbivore herd sufficiently to maintain 500 dragons.

So make the "huge cows" sea creatures, and make the dragons fishers. This is necessarily limiting, as the dragons then must live near a coast, but the sea can hold and feed huge creatures, and if the dragons can feed like certain birds, searching for signs of whales, diving, and pulling them out of the water to feast on nearby land, I'd say it passes believability muster.

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  • $\begingroup$ I know where there's a bunch of buffalo... it looks like England doesn't get to have dragons, unless just like its people, they are also masters of the sea. $\endgroup$ – Mazura Oct 21 '17 at 17:17
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    $\begingroup$ Re "near a coast": near is relative. Flamingos will fly hundreds of miles for breakfast: a much larger dragon should have a larger range. Since nowhere in England is more than 70 miles from the coast, all of it qualifies as "near". Of course, OP said "the size of England" rather than England. $\endgroup$ – Peter Taylor Oct 21 '17 at 19:54
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First: I think there is an order of magnitude problem in the OP weight given. The dragon is said to measure 40 feet and weigh 875,000 lbs. That is 396 metric tons. A blue whale is 100 feet and 173 metric tons. A sauropod is between 80 and 100 metric tons and many of them were longer than 40 feet.

Let us assume this was supposed to be 87,500 lbs or 39 metric tons. That is a medium sized sauropod. It is still nearly 3 times the size of a T.Rex.

The problem is that these dragons are too big for meat eaters.
The solution: they are not meat eaters.

marine iguana with big dreams http://www.birdsasart.com/brightideas/marine%20iguana%20showing%20teeth%20_w3c7795%20%20punta%20espinoza,%20fernandina,%20galapagos.htm

Iguanas are awesomely dragonlike. They have spines and claws and sharp teeth. If you mess with them they will definitely bite you and take off a chunk. And spit it out - they are vegetarians. So too your dragons. They will do all the dragony type stuff you need and then mow their way through swaths of swamp and forests. And kelp beds, like this marine iguana whom I think would be an excellent dragon.

I will point out that vegetarian mounts for knights have some precedent. Feeding grazers and browsers off the fat of the land also has precedent. Vegetarian dragons consuming huge amounts of low quality plant food would produce huge amounts of dung which offers the possibility of a different sort of aerial attack. I will also humbly suggest that dragons endowed with a rumen would produce methane, which offers a plausible method that they might breathe (burp) fire.

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    $\begingroup$ (Or, at the very least, they are not obligate carnivores) $\endgroup$ – Draco18s Oct 20 '17 at 18:53
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    $\begingroup$ @Draco18s - I suspect probably the iguana would not actually spit out the chunk it had bitten off of you. $\endgroup$ – Willk Oct 20 '17 at 18:56
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    $\begingroup$ Deer are herbivores, right? Wrong. They are opportunistic carnivores. They'll even resort to cannibalism given the opportunity. They'll also eat dead birds, for example. And so, don't be too quick to judge a species vegetarian. Most plants don't have the caloric density of meat. And an animal looking to simply survive, will take advantage of any source of food it can find. Sure, they may not digest that meat quite as efficiently as a carnivore, but they'll still eat it. $\endgroup$ – AndreiROM Oct 20 '17 at 19:37
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    $\begingroup$ ` huge amounts of dung which offers the possibility of a different sort of aerial attack` WTF am I reading?! $\endgroup$ – corsiKa Oct 20 '17 at 21:23
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    $\begingroup$ @John - my hope was also that the dragons could eat not only crop plants but noncrop vegetation from non-arable land, including seaweed. $\endgroup$ – Willk Oct 20 '17 at 21:30
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My kids and I tell stories to each other where the dragons all just eat metal (hence their habit of eating knights and treasure).

Another option is to have your dragons eat lots of seafood. Lots of meat on a whale...

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I think the answer is likely "yes". A Spinosaurus would likely have been 41-50 feet. This is larger than your dragons. And while it is possible that these were fish eaters, there are plenty of other species of primitive carnivores.

Could they survive in England, specifically? I'm less sure about it. From Wikipedia is not clear how many a given region could support (exercise left to the reader). It is significant that a predator of that size requires there to be prey of similar size — it takes a lot of effort to hunt, if a predator has to hunt constantly, that will lead to a net decrease in size. Of course, if these predators are being fed by humans, then they could theoretically get bigger.

If I were creating a world with dragons, I'd also create giant tree-eating herbivores while I was at it. The benefit of the tree-eaters would be that they would not take up valuable land for crops (keep them in the fallow field, near the woods), they would provide plenty of fertilizer, and they would give plenty of meat (for both the dragons and the people) without needing to sacrifice valuable grain-growing land. (The need to surrender croplands for animals actually caused a few problems in the Middle Ages, this would probably provide meat for cheap).

I think your biggest concern would then be how to prevent the apatosauruses from trampling the azaleas, and the dragons from eating your neighbor's dogs.

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