How big is a dragon's hunting territory?

Question

Dragons are very territorial apex predators. They build lairs on mountaintops, roost whenever they aren't hunting, and they hunt from the sky. With their size, wings and firebreath, there is no virtually no prey that they can't take down.

They hunt over grasslands, coasts, and mountain ranges - typically targeting large animals like bison, elk, deer, bears, walruses etc. For their prey, the only way to avoid a dragon is to run for cover and hope it doesn't spot you. For that reason, heavily forested areas make for poor hunting ground.

A dragons hunting territory is the minimum ecological area that contains enough prey to safely sustain the dragons bulk. A dragon cannot leave it's own territory without infringing on that of another dragons. Hunting territories are well defined, and fiercely protected.

I'm thinking that dragons would have to be sparsely concentrated over a continent, or else they'd destroy the ecosystem by overhunting. With their wings, their territory can be as far as they can fly, and can include land and sea. I'm wondering what sort of size in square miles their territory would actually be, and how many dragons could fit on a map.

Obviously it would vary depending on the terrain and abundancy of local prey, but I'm just after a standard ballpark figure.

Assume a fully-grown dragon has a 45 foot wingspan, and weighs around 2500lb.

Edit: I don't have any information on a dragon's food consumption or energy requirements, but I was hoping for an answer that makes reasonable estimations / best guesses. Assume the dragon is like a dinosaur, perhaps; it's reptilian, but warm-blooded and sustains a large mass.

Like any animal, it tries to conserve energy wherever possible and it tries to hunt using the minimum amount of effort. There is some magic involved for it's fire breath / flight, yet assume any magic is secondary and that it still needs to eat like any other animal.

Answer 1

40-1000 sqkm per animal

This depends more on the quality of environment than the animal. Animals change their territory size drastically depending on how productive the environment. this is actually a far better predictor of territory size than the animal size.

there are two ways to go about this,

the easiest is to just look at a pack animal who pack weight is similar, 2500lbs is a small pack of lions or a modest pack of hyena. for lions territory ranges form 20-400 sq kilometers for hyena 40-1000 sqkm. again this mostly controlled by the quality of territory. Now if we assume your dragons have metabolisms similar to birds that will increase their caloric need by about 10% so I would favor higher estimates.

The harder and likely less accurate way is to calculate caloric needs, but is useful as a reality check. luckily for animals there is a rough estimation formula. Kilocalories per day = K^0.75 X bodywieght in kilograms, K is dependant on hte animals metabolism, there is a useful site that has an easy calculator)

Placental Mammal K = 72 K^0.75=(24.7)

Non-passerine bird K = 78 (26.2)

Passerine bird K = 129 (38.2)

We should treat your dragon like a non-passerine bird, that is where your largest birds are. so it needs 29475 kilocalories per day. for cattle you can expect about 100,000 calories per acre per year assuming some losses, that includes the acreage you need to farm its feeds so lets half that because your prey animals need to feed themselves. Lets half that again becasue most predators are only successful part of the time so 29475 divided by 25,000 kilocalories per acre per year, (times 365 days in a year)equals ~430 acres or ~ 2 square kilometers. That seems low but remember that is under perfect conditions 100% super productive land, no other predators, no offspring, ect. So our above estimates seem reasonable.

Answer 2

From wikipedia, female tigers require a territory of about 450km^2. Males require greater territory. That number probably varies greatly depending on geographic area and species, but for now, let's just say that a tiger needs 450km^2 on average.

The average tiger weighs anywhere between 90 and 306 kg (198 and 675 lb) (https://en.wikipedia.org/wiki/Tiger).

So, a dragon is about as heavy as 3.7 chunky tigers, or 12.6 lean tigers. If we scale this directly, a dragon's territory can be anywhere between 1665km^2 or 5670km^2! (1035 and 3523 sq. miles, respectively) A beefy dragon would, going by these calculations, require the entirety of Puerto Rico to itself. A tiny one, however, would only (only?) require an area a bit bigger than Luxembourg.

Still, a dragon has the advantage of flight, which would make it easier for the dragon to catch prey. At the same time, flight is an activity that would probably require great amounts of energy, not to mention the fact that a dragon's brain is probably pretty big, which would also consume a lot of energy.

Answer 3

The beach. All of it.

If it were not too demeaning, you could have your condors be beach scavengers. That is not apex predator, but compatible with the traditional dragon and considerable fearsomeness - there is some thought that Thyrannosaurus Rex was mostly a scavenger.

I proposed that as an answer here:

Mythical dragon diet

Large creatures live in the sea and when they die, the bodies can wash up on the beach. Thus a small area concentrates the food productivity of a much larger one, Your dragons could coast up and down hundreds of miles of beach, watching for carrion. A whale would be more than even a dragon could eat at once, and so this would allow you to have dragons with overlapping populations, which mean dragons interacting with dragons which is always fun.

Humans (and presumably other intelligent life) likes settlements where rivers reach the sea. Vulture-like dragons might congregate at such places. For a fantasy, a sky-burial type method of disposing of the dead could be interesting - a tower where the dead are brought for dragons to dispose of.

I also liked the ideas of things bigger than whales which might wash up in a fantasy world - true sea monsters. Some of them might have life in them yet, and put up a fight.