
Glacier mastery!
Tundra mastery!
Swamp mastery!
Hills mastery!
Forest mastery!
Meadow mastery!
Plains mastery!
Lake mastery!
and so on.
Also, these are likely to be included:
Mastery of tracking (makes it easier to find animals, tracking-mode takes less ep and so on.)
Master hunter (improves damage dealt with the initial attack, makes the skins worth more, has a positive impact on the size of hunted animals (weight, not exp value), acquired solely by the number of kills done while hunting)
Unfortunately, rangers have all those nice terrain/animal thingies already, so they might want to keep them for themselves...

Oh, and it will take time to raise all those terrain masteries to 100, so I can't see why our eternal hunters (players that like to hunt 24/7) wouldn't like them to be added.
And as always, these masteries don't have to be uber great, just something to separate the dedicated from the whimsical hunters, something to brag about, nothing too good, to make this subguild special enough to be joined, since some just raise the necessary skills by doing.
I posted this one here and not into the Ideas, since this guild already exists.