NotSpaghetti
A green goose is a spring one - young, "green" geese are more delicate and tender. They would have fed on fresh spring grass and greens, rather than being fattened up on grain or harvest leftovers later in the year. I think Christmas Geese were "Stubble Geese".
I don't remember Mansfield Park at all but they were considered a seasonal luxury.
Thank you for the explanation of a green goose NotSpaghetti. I had always thought it referred to the colour of the goose.

