Why is the plural possessive of moose spelled moose's instead of mooses'?

Answer 1

Since the plural form for the noun moose is the same, moose, the singular possessive moose's, and the plural possessive, moose's are the same.

Example:

We found a moose's footprints in our garden.

We found several moose's footprints in our garden.

Answer 2

The plural possessive of "moose" is "moose's" instead of "mooses'" because "moose" forms its plural by changing its internal structure (irregular plural). "Moose" does not add an "s" when pluralized, so the possessive form simply adds an apostrophe followed by an "s" to indicate ownership by multiple moose.