For me, the epitome of high fantasy is a troop of warriors on flying mounts. But what would it really take to support enough griffins to mount more than a few riders? How much would they eat? Here, we will dig into how much a griffin mount might eat. Next up, we’ll look into whether a griffin can really fly at all.
For those who don’t need the details, it seems to work out to about 17 to 26 head of cattle per year per griffin depending on the work load. Weapon finds from early post Roman Era in the Germanic lands indicate a petty king might have a troop of 90 mounted followers. Put them on griffins, add remounts as griffins get injured and breed, and such a troop might require 180 griffins consuming the equivalent of 3600 head of cattle per year. Some of that might be hunted on the wing but that’s a lot of meat. Cavalry units in various periods could be much larger (many hundreds to thousands). Voracious as they are, on the face of it, it seems they would most often be used for scouting, as couriers and as raiders than as a significant military unit.
But fantasy is all about bending the rules so if you are doing a game world or a novel setting with troops of 1000 griffins, don’t let this stop you. It won’t stop me.
This isn’t a thesis on the topic so I’ll admit sources are limited and there will be a certain amount of hand-waving.
Obviously, there is no real-world data for feed-cost of a griffin but I will use Earth-creature data to extrapolate some figures since there has been a large amount of research on energy budgets, moving and rest energy, and so on for a wide range of creatures. My primary source for this is the discussion and charts at Food and Energy Data. Information on how much a tiger eats is mostly from Research: Management of Captive Tigers, Chapter 4.
Now for my assumptions:
- Griffins are carnivores: All large flying creatures on earth on carnivores (raptors, pterodactyls, etc.) and most fantasy griffins are carnivores (griffons, dragons, not sure about hippogriffs).
- A griffin can carry a rider and gear equal to 20% of its weight: this is a judgment call (otherwise known as a swag). While raptors can carry a little more than half their weight in prey in their talons, it seems that this is for a short distance to a nest or feeding spot (5 minutes or less of flight) and that for prolonged flight, 20-25% is more reasonable.
- The mount’s energy consumed in flight (its energy budget) when creature carrying a load is (1 + load-as-percent * 2.0) compared to its unloaded energy budget: I assume there is inefficiency in carry a load. For example, a load of 20% of its weight means its energy budget is 1.4x its unloaded energy budget. All this means is that a 1000 pound mount carrying at 200 pound load consumes as much energy in flight as a 1400 pound mount carrying nothing.
- Our griffin weighs 1000 lbs: this allows for a 200 pound load: a 165 pound rider plus his gear. Naturally, a sturdy 200 pound warrior needs a bigger mount and an elf or human female could get by with a smaller mount (or alternately, fly the mount faster or at less feed cost).
- Max Energy to Min Energy consumption is 7:1 for the griffin: From sources I’ve found, it seems the normal animal range is 3x to 7x. This matters as the high peak energy of flight means that the rest energy of the animal is higher. Put another way, a 1200 pound horse will have a lower rest energy consumption than a 1200 pound griffin. A higher ratio means the griffin will consume less food over all so we are cutting our griffins a break. I’ll assume flying creatures and our griffins in particular are more efficient at rest than our normal creatures and go with 7x. For a dragon, I would be inclined to use a higher value in the range of 15-20x.
- Landed-activity to rest activity ratio is 2:1 for the griffin: The griffin, when on the ground walking about or eating consumes more energy than at rest, but we’ll go with a lower bound of twice the rest energy assuming it is just ambling about and not bounding about wildly. For the equivalent land-only creature, the activity ratio is 2.5:1, active versus resting: A predator like a tiger might exceed 2.5x rest energy consumption briefly (a few minutes) during a kill of its prey but I’m going to assume that is a negligible amount of its energy budget compared to the hours on the prowl. For something like a cheetah, there is more high energy time per kill (5-10 minutes) but it is still a relatively small amount of time in the life of the predator and for this analysis, I’m going to ignore it.
- Soaring and gliding requires 35% the energy of active flight: This probably varies wildly by terrain and season and this number is just something I pulled out of thin air but let’s go with it for now. Yes, sail planes can soar for extended periods at no energy cost but I’m assuming our griffins are not as efficient as that- it takes energy to support the wings while soaring and the rider will cause the creature to enter periods of more active flight to keep it in the patrol region. In for a fantasy RPG, perhaps skill in aerial mount of the rider can translate to more or less efficient soaring.
- Flight speed is 25 mph: on the one hand, this matches flight speed of many birds. On the other hand, something as heavy as a griffin would stall at these speeds. I don’t think a griffin can really fly at all so this is something we will just have to wave our hands at. From an aesthetic point of view, I like griffins flying at bird-speeds so we will go with that. Descent or dive can be treated as soaring for energy use and climbing (at a lower speed) as the same energy consumption as flying at the 25mph speed (i.e., both represent max energy consumption).
- A large tiger weighs about 550 pounds and eats about 14 pounds per day.: The weight is for a larger, male tiger. My feed data is not calibrated by tiger weight and may be under-called for the larger tigers. Food per day is in the middle of most sources and puts a tiger’s daily allotment in this range. Tigerlink suggests this is appropriate both for captive tigers on a daily feed and wild tigers who will gorge on a much larger kill then not hunt for days after. (That is, the hunting tiger averages 14 pounds per day but eats less frequently.)
- 70% of a prey animal, by weight, can be consumed by our griffin and our tiger, which is from my tigerlink source. Seems like a reasonable number. Other sources indicate yield from a beef-steer is 62.5%; maybe tigers are less picky than humans. Our feed cattle in this exercise weighs 1350 pounds: This is supposedly the average feedlot weight of steer. Steer herded with an army would likely be less but this seems a good enough number.
First thing I realized when digging into this, although it makes perfect sense on reflection: it costs more to walk than to fly. That is, to move the same distance, an animal expends less energy flying than by walking although this benefit decreases with increasing weight of the creature. Of course, a flying creature can cover a lot more ground than a walking creature in the same amount of time so while its energy per unit distance is less, its energy per unit time of motion is much higher. Flying does provide certain efficiencies in path: you can pretty much fly from point A to B in a straight line but walking may take 1.2 to 2x or more the straight line distance as the trail meanders.
So, how to actually determine feed amounts? Given the assumptions above, we simply need to determine, by extrapolating from earth creature data for each the following:
- Feed cost of active flight: This is flight in a straight line, with minimal gliding and soaring. I will use this for directed flight from point A to B.
- Feed cost of soaring flight: This is flight that uses as much gliding and soaring as possible, leveraging thermals, etc. This is for a patrol or hunting above a fixed region where mount can seek out thermals and is not set on a specific path.
- Feed cost of activity on the ground, such as eating: The cost of walking around on the ground. Probably not a significant factor for our mount, but it is part of its daily activity.
- Feed cost of rest on the ground: Sleeping and dosing take energy.
The methodology used here is as follows.
- Determine the energy that the tiger gets from a pound of food by estimating the energy expended between kills and the food per kill.
- From this scale to the griffin to determine its feed costs for each activity.
- Create some typical profiles for our griffin to represent days flying to a destination, days in patrol, days at rest.
- Determine the feed cost of each profile.
- Extrapolate this to a unit of griffins of various sizes and compare to feed and fodder requirements for cavalry and human infantry.
Step one: from my tigerlink source, lets assume the tiger feeds exclusively on 400 pound Sambar (a medium prey animal). Each Sambar provides 280 pounds of meat (70% of 400) which will last the tiger 20 days. Let’s assume, allowing for failed hunts, he spends 40 hours of that 20 days (240 hours) patrolling his territory and hunting.
Extrapolating from a graph in my first source that shows energy use by weight for flight and land movement, I have the following energy costs for an hour of activity at the speeds below. We will use the 5 mph as the active, land creature activity and the 25 mph as the active flight activity.
- 1000 lb griffin carrying a 200 pound load: 0.28 J/(foot * lb), which at 25mph is 36.6 MJ per
- 1000 lb griffin on the ground: 0.35J/(foot * lb), at 5mph, this is 9.2MJ/hour.
- Compare to 550 lb tiger: 0.42j(foot * lb), at 5 mph 6.0MJ/hour.
If our tiger takes 280 pounds of meat to do 40 hours of active prowling and 440 hours of rest, and as stated before, his active to rest ratio is 2.5 to 1, then our tiger must expend 1.3 billion Joules for that 280 pounds of meat, or each pound of food must provide 4.7M Joules of energy if he isn’t going to starve.
Using 4.7M J / lb of food, the preceding table and our assumptions, for our griffin, the pounds of food required per hour of activity for each type are:
- Active flight requires 11.1 lbs of meat per hour
- Soaring Flight requires 3.9 lbs of meat per hour
- Ground activity for the griffin requires 3.2 lbs of meat per hour
- Rest for the griffin requires 1.6 lbs of meat per hour
Compared to the tiger:
- Ground activity of 1.3 lbs per hour
- Rest activity of 0.5 pounds per hour
Note: the Griffin’s rest activity is limited by the 7:1 max to rest activity ratio. The griffins have a high metabolism.
Now for some typical profiles for our griffin that capture the amount of time spent at various activity levels.
- Straight flight is 150 miles per day, 5 hours of active flight, 2 hours of soaring, 2 hours on the ground, the remainder is rest. This requires 96 pounds of food or 0.1 steer, or 1 steer per 10 days of this activity.
- Distant patrol (25 mile distance, 2 hours on target). 2 hours of active flight, 2.5 hours of soaring, 1 hours on the ground, the remainder is rest. This requires 68 pounds of food or 0.07 steer, or 1 steer per 14 days of this activity.
- Local patrol (4 hours over camp), 0.5 hours of active flight, 4 hours of soaring, 1 hours on the ground, the remainder is rest. This requires 57 pounds of food or 0.06 steer, or 1 steer per 17 days of this activity.
- Rest requires 44 pounds of food or 0.05 steer, or 1 steer per 22 days of this activity. So, a day of hard flight will take nearly 100 pounds of meat. Or, put another way, a griffin will consume a steer every 10 days if
flying hard for 10 days. (That’s a lot of flight. The griffin probably needs 1-2 days of rest per day of flight like that.)
Alternately, if the griffin is sitting around during winter doing nothing, it may consume a steer every 22 days. At a siege where it is mostly just surveying the enemy fortification, it might consume a steer every 14 to 17 days. This means, three weeks per steer when idle and two weeks per steer when busy. These seem like reasonable numbers to me but you could argue for fewer or more steer as you see the data.
This may not seem like a lot of steer but consider a small squadron of 4 fliers might need 4-6 mounts. That’s 70 to 160 steer per year. A troop of 40 fliers would need 700 to 1600 steer per year. That’s a lot of beef.
What do to with this?
If you are building a game world or writing a book, you can, of course, ignore the problem of feeding the griffins. It is a fantasy world after all and much more needs to be over looked to make it work. But you can also use the griffin-feed issue to round out the world. Maybe griffins are the true prestige symbols for nobles, affordable by only the truly rich? Or perhaps one country is invaded by another who is temporarily able to exploit the griffins even if long-term, they can’t keep their large griffin forces fed. Might even make for an interesting back-and-forth: Kingdom falls to conquerors on griffins, the conquerors settle in, lose their griffins over time, the oppressed rise up.
Sometimes the awkward “facts” can simply enrich the story.