I hear them in Luxembourg twice every year. I love their calls, and I love how they help each other. I've watched them for hours and seen a few cases where they will stop and turn in a place, a few smaller groups getting together, then leave a bird to wait for the next group, and when they arrive at the same spot they stop and turn in the air too. Then they too leave a bird or two until the next group comes. It is rare to see it, compared to when they only fly over but it is magical when it happens.
Amazing to see them fly so high in the air up close!! Can't believe they make this journey without being covered in metal and burning engines- hope they get enough food and rest to get to where they are going!!
