Heat oven to 375 degrees. Rub game hens with salt and pepper and dot with butter. Stuff cavity of birds with tarragon and place a sprig on top of each. Place in oven and roast until tender, basting several times.
When hens are tender, place on a platter and keep warm.
Place pan with juices over high heat, and de-glaze pan with cherry vinegar. Add vanilla bean, sugar or honey, tarragon and port, and mix well. Add cherries and cook until cherries are tender and pan liquor has reduced by 1/2. If cherries are tender but the sauce hasn’t reduced enough, spoon cherries into a small bowl and continue reducing liquor.
Add vanilla if using extract, otherwise, remove bean, adjust seasonings, put cherries back into pan to heat if necessary, then pour over game hens and serve.
Especially nice served with wild rice pancakes or wild rice pilaf.