Briefly on world setting: Roughly classical age technology, magic is rare, difficult and shunned, flora and fauna is inspired by a remix of the Neogene period.

Practical concerns for long distance travel on kradjin

I’m writing about two people who are traveling through a forested area on terrorbird-analogs (based on titanis Walleri) called kradjin. I was hoping to get some input on practical concerns while traveling with these kinds of mounts. Any input would be great, but here are some specific things I have been wondering about:

  • How often and how much would a terrorbird-analog need to eat while being used as a mount?

  • How far can it be ridden between rest stops and how much ground can it cover in a day.

  • How fast and how long can it run with a rider on back if it’s running speed without a rider is 65 km/h.

I’m basing the design of the body on a terror bird called titanis walleri. It was 2.5 metres (8 ft 2 in) tall and weighed approximately 150 kilograms (330 lb) with a heavy build of the body and a large axelike beak

The morphology of the kradjin might differ from the titanis though, considering it has been used as mounts by humans for thousands of years. But I’m working under the assumption that it will have roughly the same height, weight and build.

In this world a few different flightless birds are used as mounts and the most common ones are herbivorous, but this one is a pure carnivore.

More info on the kradjin that might or might not be important to answer the question

The kradjin are highly intelligent and social animals who have lived close to humans for millennia. They have not been actively kept or bred in a systematic way, but they have a symbiotic hunting relationship with the humans in their native area that has advantaged the birds who are more social with humans. Similar to some parrots they can bond with specific humans and choose to go live with them instead of being with other birds. The humans in their native area do not treat them like property, and consider them to be equals. It is a great honor to have a kradjin bond with you. In other areas away from the native lands kradjin are beginning to be tamed and trained for riding and warfare

  • $\begingroup$ How is its digestive system? You might look at how many calories are in the meat it eats, and how much energy it takes to carry a load, based on modern animals. $\endgroup$
    – JDługosz
    Commented Jun 14, 2016 at 17:25
  • $\begingroup$ I'm working on something like that, but it is difficult when we don't have any purly carnivorous flightless birds of this size around anymore. I'm reduced to making assumptions and many assumptions at that. And in that regard having input from other people would be of great help. $\endgroup$ Commented Jun 14, 2016 at 17:29
  • $\begingroup$ So use physical limits and thermodynamics as a boundry: you can't do better than that. Details are then due to results of selective breeding, and not at all natural. $\endgroup$
    – JDługosz
    Commented Jun 14, 2016 at 17:32
  • 1
    $\begingroup$ You may be interested in this question $\endgroup$
    – Kys
    Commented Jun 15, 2016 at 14:09
  • 1
    $\begingroup$ See also this hard-science question. It brings up some good points, like the lightness of the skeleton working against you. $\endgroup$
    – JDługosz
    Commented Jun 15, 2016 at 16:32

1 Answer 1


Disclaimer: I am no authority on biology. Even if I were, I don't have a live titanis nor a lab to come up with hard data. I am really making up stuff here.

We know that birds are warm blooded animals, and we know that flightless birds such as ostriches lack the flight-related adaptations that most birds have. We could then extrapolate that the metabolism of your birds could be like that of a similar sized mammal, or that of an ostrich, or something in between.

I am also thinking about how much weight they can carry. If you google "weight of a horse" you get a figure of 380-1000Kg. Since titanis weighted around 150kg, you could say that it could carry half the load a small horse could, if you domesticate them and breed them for load-bearing.

But you don't want them for workhorses, you want them for mounts. Let's look at the closest thing to them we have in our own world.

Ostriches are somewhat lighter, at around 120kg for males, and 100kg for females. Humans have been riding them for millenia, and it is even considered a sport in some places.

I don't have the figures for how long an ostrich will allow itself to be ridden. And Wikipedia only has this to offer on the subject of rideability:

The ostriches are ridden in the same way as horses with special saddles, reins, and bits. However, they are harder to manage than horses.

Out of the box, this means that your birds can take a human rider probably better than an ostrich could (due to their extra weight). Being the carnivores they are, though, I think it's less likely that they would let you mount them. Again, breeding for millenia, which is done in your world, may solve this.

Now to your specific points:

  • How often and how much would a terrorbird-analog need to eat while being used as a mount?

Look at the figures in the first table from this page. Adjusting for weight, I think your birds could survive by eating 2.6~2.7kg of ration per day. Three feedings a day could keep your birds healthy and happy.

  • How far can it be ridden between rest stops and how much ground can it cover in a day.

Ostriches and horses have evolved to cover large distances in a day. Your birds could have followed that same direction in their evolution history.

This question has figures for horses. Some can walk around 20 miles (~30 kilometers) in a day. In some situations they may go further - check the accepted answer.

  • How fast and how long can it run with a rider on back if it’s running speed without a rider is 65 km/h

The bodily weight-to-load relation of your birds is less favorable than that of a horse. They might be great for long distance riding if they walk, but not great for chases or racing. They would probably be outran by horses.

But still, even if their top speed with a human on top is around 30km/h (20mph), that is MUCH faster than a human can reach on foot. This wiki states that the record speed for marathonists is around two thirds of the figure I just provided - and most people are not marathonists.

One last thing: you are riding a carnivore. You might want to keep them muzzled most of the time, and cruel as it may sound, probably clip their claws. A strong level of rapport between bird and rider may also be a necessity. And they might take less abuse than a horse before they lose their temper, so be nice to them.

  • $\begingroup$ I thank you for attempting to answer this question. I realise it might not have been the best question for this site, but I learn best from trying. However you have given me some interesting input and I will mark your answer as accepted so that I can move on from this question and go on to asking better ones. $\endgroup$ Commented Jun 20, 2016 at 13:31

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