Preheat oven to 375°F (190°C). Grease a 12 - 2 3/4 x 1 1/2 inch muffin cups.
In a large measuring cup or bowl whisk together the egg, buttermilk, oil, and vanilla extract.
In another large bowl combine the flour, sugar, baking powder, baking soda, salt, and orange zest. Gently fold in the berries. With a rubber spatula fold the wet ingredients into the dry ingredients and stir only until the ingredients are combined. Do not over mix the batter or tough muffins will result.
When filling the muffin cups, trying using two spoons to prevent the batter from dropping outside the cup. Place in the oven and bake until a toothpick inserted in the center of a muffin comes out clean, 20 to 25 minutes.
Transfer to a wire rack and let cool for about 5 minutes before removing from pan.