My Magic System
All of this stuff about my magic system is actually necessary, because I know no-one reads links provided to them and because there is magic in my world.
Brief Overview of Magic
Magical powers fall under seven broad categories. Air, water, earth, plasma (fire/lightning), plants, light, and animals. Animal magic is tricky, because living things resist magic. But, many animal mages can influence animals, and some can control dead animals (this is called necromancy and is a big societal no-no.) The strength and scope of magic varies from individual to individual. But, these are the most common in order. Earth, water, air, plants, animals, plasma, and light.
These magical capabilities are like the show Avatar, the Last Airbender, in how controlling magic works. However, in my book magic is much less powerful. For instance, an earth Mage may only be able to influence as much dirt as they could lift, and lifting this dirt would take about as much energy as doing it by hand, except you don't have to touch it, and it could be a perfect brick shape. No force is exerted in separating the dirt or material from other similar material attached to it. So if you were to pull this rock in two, that would take little effort, other than the force of pushing the pieces apart.
Magic is like a muscle that is really hard to develop.
Magic on a larger scale
The level of magic described above is only about 75% of magic users. Everyone else is more powerful.The strongest people can do things like shoot lasers, uproot trees, be human flame throwers, make zombie hordes, create small tornadoes, cause rovers to overflow or to break dams, or cause small earthquakes. This is about 7% of the population. Everyone else is in between.
Magic on a smaller scale
I'll just make a list of some possible fighting applications of magic. Ice daggers, water whips, wind influenced arrows, starting fires, shooting small fireballs, throwing stones, moving stones, strangling people with vines, tripping up enemies with plants, scaring/exciting horses, and flashing people. (With lights!) These are of course by no means the only applications of magic.
Living things are resistant to magic, proportional to their intelligence/self awareness. So it would be easiest to make a swarm of spiders, then harder to make boars attack (your enemies, and not yourself), and nearly impossible to make someone slap themself. There is a type of stone resistant to magical tampering, which is found deep underground, near bedrock. Also, bones are immune to magic.
Note - These things are resistant to magic being influenced directly upon it, not magically influenced material. A rock thrown by magic at someone is just as effective as a rock thrown without magic at the same speed.
Thunderbirds fly ahead of approaching storms, preying on pretty much any animal larger than a goat. However, they don't generally attack anything the size of or larger than a buffalo. So your buffalo herds are generally safe, with an occasional calf stolen. People often own pigs, goats, sheep, cattle, horses, and a tamed livestock version of terror birds. These birds are used as pack animals.
These birds are just that, large birds of prey. They have no magic. As for their size, they can carry up to 1200 pounds, so plan for their size accordingly. Comparatively, a bald eagle can carry 5-6 pounds. (I'm not really sure how much they'd have to eat, so that can be an optional part of the question.)
This is all taking place in medieval times. Assuming it rains about once every week, how would this affect ranchers and the like? Would they have special shelters for their livestock when it rains? After all, you don't want your entire flock of sheep munched by a giant bird. Would squads of magical people shoot fire at giant birds?