Easy way to tame them early game or as a first tame:

Spawn in the bottom left area and get situated (around level 20).

Few things are necessary:

1: Hide armour at least.

2: Bloas, Basic tools from wooden crates, ability to kill creatures when needed (mainly spiders and scorpions).

3: Locating the Emerald river. Wyvern-Trench esk rocks on the coast.

4: Enough blood packs. Repeatedly kill yourself by acquiring your own blood and respawn at sleeping bags or a bed.

Enter cave and do some simple mass murder. Head to the right on entrance as there’s less typical cave creature spawns and more desmodus. Using a spyglass you will have (crystal can be gathered at the emerald river), look for a relatively low level or something alone. Get nice and close and fire an arrow at it. It’ll be scary when it comes to you and you’re on the ground, but even if it doesn’t work, what’s there to lose. You’re only low level. When it picks you up, since it’s a low level, it’ll likely tame quite quickly. Whistle follow and quickly run away with your new pet bat or otherwise fend off the other bats. Or maybe tame them too.

Taming low levels is very easy to do, it’s a great way to get started on the map. It can’t do right much for now, no saddle. So it can protect you until you’re high enough level, look cool as hell, and be whistled to attack to get blood backs which allows you to make elixir. Easier taming. I believe it is craftable without the saddle, but don’t count on it. Enjoy your easy bat.