I’ve been playing with this a lot - I’m pretty sure there is an increased spawn rate in icy/snow biomes. Though as posts above say, could be the snow itself causing the increase, so still somewhat right, haha! (Those biomes have more snow, though I’ve seen big packs spawning without active snow in the area) 
They do spawn in other areas but rate seems lower.
I set up this planet to sort of test it more. It is off Circ, and a good hunting ground for any who want to use it. Check the two videos there, you’ll see what I mean on the spawns, was doing very well on the big ice crack biome here - [Hat Trick] --[T4 - Inhospitable Lush Sovereign World]-- [Active]
Another good spot is around the Skyrim portal, access at TNT Flan, running around there hunting was getting me a lot too.