Polar bears and grizzly bears cross over into each others territory,
and so occasionally polar and grizzly bears will mate and conceive.
The hybrid, let's call it a Polar/Grizzly
will be raised by its mother, whichever bear breed that might be.
If the Polar/Grizzly hybrid's mother is the grizzly,
the cub will be raised to scavenge carrion, graze on grass and forage for berries.
If the Polar/Grizzly hybrid's mother is the polar bear
the cub will be raised to stalk sleeping seals on the ocean's frozen water.
If a full grown Polar/Grizzly raised by a grizzly
were to find itself smack in the middle of strict polar bear territory,
it most likely wouldn't survive the night unfortunately,
because it wasn't raised to survive that way, despite it being a Polar/Grizzly.