Cascadia · Board game rules
Can a Fox C be placed on a terrain tile already occupied by another Fox C?
Quick answer
No — each Habitat Tile can hold only one Wildlife Token total, so a Fox token can never be placed on a tile that already has any token (including another Fox).
Details
The Wildlife Token placement rules state that a token may only go onto a Habitat Tile that "must not already have a Wildlife Token on it," meaning each tile can support at most one Wildlife Token, regardless of species [p.7 — 2 Place the Tile and Token into Your Environment]. This applies universally, so it doesn't matter whether the existing token is a Fox or any other animal — the tile is simply unavailable for a new token once occupied.
The "Fox C" scoring card itself only affects how points are calculated (based on similar animals adjacent to a fox), not the placement rules for tokens [p.11 — Wildlife Scoring Cards]. Placement of any Wildlife Token, including Fox, always follows the general one-token-per-tile rule [p.7 — 2 Place the Tile and Token into Your Environment].
Watch out: Don't confuse adjacency (which matters for Fox scoring) with occupying the same tile — two Foxes can be adjacent to each other on separate tiles, but never stacked/placed on the same single tile.