Building the farm
Note: See if there is a tent, sauna or house nearby that you can access so the animals can respawn.
You then can simply try to place an item there and when you see a red circle similar to the one below you know that you found a spawnpoint.
Now all you have to do is circle the red circle with fences and leave a wide pointing opening that gets smaller towards the end. This will make the birds/reindeers run into the opening and get stuck there.
Farming
Now just grab a chainsaw and start killing the birds/reindeers. Once all the animals are dead enter and leave a tent, sauna or house that is nearby and the animals will respawn instantly.

