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What would be the daily calorie requirements of a flying creature that could carry 200 lbs on its back? Are there features that could make a significant difference in this calculation (cold blooded/warm blooded, mammalian vs reptile, marsupial vs egg laying ect)? (If evidence is brought that supports a significant difference in calories needs based on this I will clarify my question.)

In nature I think the wyvern would only fly to hunt for food, to find mates, and to look for new nesting grounds. Though domesticated ones would have a more aggreesive flight schedule and need more food.

As for how high/far/fast, pick options that tend towards lower calorie requirements. Evolutionarily speaking, lower calorie requirements makes it easier for the animal to survive (unless it's too slow to catch prey).

I'll include that the planet is currently earth. Azuaron's answer may end up being the best. I chose 200 lbs because I knew it was at the very extreme end of what could be possible, if it even was.

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    $\begingroup$ Does this article answer your question: en.wikipedia.org/wiki/Kleiber%27s_law ? $\endgroup$ – cobaltduck Jun 9 '17 at 15:49
  • $\begingroup$ @cobaltduck It provides supportive information. Although it is called a law from a read through it looks more like a theory right now. $\endgroup$ – PCSgtL Jun 9 '17 at 16:07
  • $\begingroup$ @cobaltduck I read the page but it seems like most of it is saying how poorly the theory seems to work outside of specific sizes and at that only accounting for base metabolism. $\endgroup$ – Adrienne Jun 9 '17 at 18:18
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    $\begingroup$ @Adrienne (and also OP): I merely wanted to draw attention to the idea that there has been research on the relationship between an animal's mass and metabolic rate, and that there have been results - albeit still debated- that could serve to provide a first estimate. // While I am here, mandatory xkcd reference: what-if.xkcd.com/78 $\endgroup$ – cobaltduck Jun 9 '17 at 18:35
  • $\begingroup$ Very much related: What efficiencies make a realistic food chain? $\endgroup$ – a CVn Jun 10 '17 at 16:54
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So I did some math by comparing beasts of burden to flying critters and their caloric intake and requirements.

A Bald eagle will consume about 1 pound of food a day with an estimated calories of 832. This number is likely small but is the best I could find online. A Bald eagle weighs about 3 kg.

A horse doing moderate work is recommended to have a daily intake of 25000 calories. To carry a person weight, assumed 100 kg, the horse needs to be at least 500 kgs. This is our best bet on how much a wyvern would have to weigh at minimum to carry a human rider for any amount of distance.

taking into account their calories per kg ratios and applying the ratio of the eagle to that of the horse ends up with requiring 138,000 calories a day to carry around a rider on their back. Now this is assuming that they have a metabolism similar to that of a birds which as non-birds is probably inaccurate but that number can give us an estimate on how much they might need. Also this number is likely most accurate for a wyvern in nature. This means that the creature would need a much larger likely half again as large of a diet to be healthy. Also this number is likely on the low side in ways that I can't account for but guess would mean upwards of an additional 20-50% more calories due to caloric intake not being a linear in relation to mass. This brings us to a total of 312000 calories a day. Or in more easy to digest terms 320ish pounds of 85% lean ground beef a day per wyvern.

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    $\begingroup$ metabolic needs do not scale linearly, you can't just multiply X eagles and say that is what it needs. one 100lb eagle would eat far less and need fewer calories than a hundred 1lb eagles. $\endgroup$ – John Jun 10 '17 at 19:06
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    $\begingroup$ @John the more important question though is which would win in a fight $\endgroup$ – PyRulez Jun 10 '17 at 19:25
  • $\begingroup$ Also the wyvern is cold blooded (I assume), I'm not sure if that will impact it... $\endgroup$ – Liath Jun 13 '17 at 14:43
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I would start with a logarithmic Average, I know that Humming Birds have rather high intakes, insanely high actually, I'm rather surprised they survive as a species honestly, whereas a horse, we know what it takes to fire that hefty hunk of muscles I'm fairly sure, keep in mind, I don't actually have any of these exact numbers on me, I'm simply offering ideas to at least attempt to give you a coherent answer using the knowledge which I am familiar with.

There's also Elephants, Whales, Wildcats, and any other Large Creatures that you can get the intake Data on, remember to regulate your Weight values, some might give you kg whilst others give you g and others (eg. Whales) might be measured in T (I know 1 Ton = 1,000 kilograms = 1,000,000 grams = ~2,000 Lbs. for reference).

You likely need to figure out the average intake per pound across the various Species. I believe your question Title specified Wyverns, which I believe are regularly Cold Blooded, Egg Laying, Reptile types, which would make Snakes a good comparison, you probably want slightly larger than "Titanoboa" (extinct Ancestors of modern Snakes), depending upon Size and Activity Levels you might need to adjust accordingly.

One hypothesis I've heard for real Dragons being currently extinct is simply a Lack of Food, they were so Massive, that they couldn't Hunt anymore, probably didn't even have enough Energy to Fly, it simply starved to Death in a field somewhere in most cases, our at least that's the Theory.

If you can at least figure out a decent average intake, you should be able to get a decent portion for your Flying friends.

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  • $\begingroup$ I would like to note, that conversion table is using Metric, not US Standard which lists (1 T = ~1,800 Lbs), or the European standard which I'm not as familiar with, but instead the Global Standard Metric. $\endgroup$ – Blue64 Jun 17 '17 at 13:52
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The bird would need to be at least 100 lbs. 300lb would be a better guess. Wing span, would be really immense, and probably have to be kinda fast beating to make it smaller. Such as 20ft wingspans. I would guess they would need to eat up to 1/3 their weight each day. Chicken is 750 calories per pound. A 100lb wyvern would need 75K calories minimum per day. Up to 225K calories, or 25 chickens per day, for the 300lb wyvern.

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    $\begingroup$ This would mean they could carry nearly double their body weight. It's more likely the margin is going to be something like 5-10% additional weight beyond their own bodies, for any kind of long distance travel. Flying ain't easy. $\endgroup$ – MichaelHouse Jun 9 '17 at 19:32
  • $\begingroup$ Andien condors carry 1.5 times their weight. $\endgroup$ – Wally Jun 11 '17 at 0:33
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    $\begingroup$ I'm sure that's possible, for very short periods. You want a beast of burden to be able to go for hours. $\endgroup$ – MichaelHouse Jun 11 '17 at 0:54
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Science-based: A flying creature cannot carry 200 lbs on its back, so determining how much food such a creature needs is impossible.

The world record for largest lift weight by a flying creature is a bald eagle that lifted a 15 lbs mule deer. Alaskan bald eagles (such as this one) have been known to weigh more than 17 lbs. There's no note as to how far this particular eagle was able to lift this particular mule deer, but it's likely not far. Generally, eagles are considered able to fly normally while lifting half their body weight.

Say we're generous, and eagles can fly normally with 3/4 of their body weight. That means a 17 lbs eagle can fly normally with a 12.75 lbs animal in its claws. Or, in other words, a 17 lbs eagle can lift about 30 lbs in the air (its own weight plus the weight of the animal it's carrying).

Let's now talk about the largest known flying animal, the quetzalcoatlus, which probably weighed around 500 lbs (if we're feeling generous; other estimates place its weight around 150 lbs). Now, you may think we're golden, because 3/4 of 500 lbs is 375 lbs. But, we have to take into account the square-cube law. Simply put, the square-cube law states that while area of something (for instance, wing surface area) increases at a squared rate, the mass will increase at a cubed weight.

Bird lift generation is directly proportional to the surface area of the wing. The wing chord of a large bald eagle is 27.2 inches. The wingspan is 90 inches. Let's be extra generous and say that the entire bird counts as wing, and the entire wing is the width of the chord. That gives our bald eagle 2448 square inches of wing (17 square feet). So, 17 square feet of wing can lift 30 lbs into flight. Hold that number.

Quetzalcoatlus had a wing span of 36 feet and a wing chord of about 4 feet. Using our same generous estimates, quetzalcoatlus had a wing surface area of 144 square feet. Quetzalcoatlus' wing surface area is 8.5 times the wing surface area of the bald eagle. 8.5 * 30 = 255 lbs. Our back of the napkin math states that quetzalcoatlus can't even fly its own weight if we use the largest weight estimates quetzalcoatlus.

But, maybe that's because our wing estimates are double what they should be (bird wings are more like triangles than rectangles). Let's run the numbers again, but with bald eagles having 8.5 square feet of wing and quetzalcoatlus having 72 square feet of wing. This makes quetzalcoatlus' wing surface area 8.5 times the wing surface area of the bald eagle... which is exactly the same number we got before. The important point here is that the relationship between the two needs to be correct, not that the exact numbers are correct.

We can see the same thing happen with land-bound animals that scale up: an ant can lift many times its body weight, a human cannot. An elephant that jumps down from a chair will break its own legs. Similarly, a shrike is said to be able to lift much more than its own weight, while a bald eagle can't even lift its own weight. Extrapolating out to a size that could carry itself plus 200 pounds, such a creature cannot exist on a planet with Earth gravity and atmosphere.

The other major problem with this scenario is the phrase "on its back". I want you to flap your arms and pay special attention to your back muscles. Now imagine doing the same thing in midair with 150 lbs strapped to your spine. To be able to fly, creatures need unrestricted range of motion for their shoulders and back muscles. The only way to strap something to the back of a flying creature is to strap something that's so small the creature barely notices it. In our case, that would mean something many, many times the size of the largest ever flying animal.

But, even if you put people in a basket the wyvern carried in its feet, it would still never get off the ground (as illustrated above).

See this answer to a meta question. This question is based on false premises (a flying creature that could carry 200 lbs on its back in a science-based world). From the science-based tag description: "For questions that require answers based on hard science, not magic or pseudo-science, but do not require scientific citations." (emphasis mine)

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    $\begingroup$ I appreciate you taking the time to go into this. On my own I would not have known to apply the squard-cubed law to this. I don't feel your reasoning for the "on the back" portion is as strong, but all in all a great answer and help to what I am working on. $\endgroup$ – PCSgtL Jun 12 '17 at 21:05

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