1. In a large bowl, stir together flour, sugar, baking powder, baking soda, and salt. In another bowl, mix egg yolks, buttermilk, and butter until well blended. Stir egg-yolk mixture into flour mixture just until well blended.
2. In another large bowl, with a mixer on high speed, beat egg whites until soft peaks form. Gently fold into batter until no white streaks remain.
3. Place a nonstick griddle or a 12-inch nonstick frying pan over medium heat (350°); when hot, coat lightly with butter and adjust heat to maintain temperature. Spoon batter in 1/3-cup portions onto griddle and gently spread into 4-inch rounds; sprinkle evenly with about 1 tablespoon each blueberries and raspberries. Cook until pancakes are browned on the bottom and edges begin to look dry, 2 to 3 minutes; turn with a wide spatula and brown other sides, 1 1/2 to 2 minutes longer. As pancakes are cooked, transfer to baking sheets and keep warm in a 200° oven. Serve warm with maple syrup.