To measure the wingspan of a bird , a live or freshly dead specimen is placed flat on its back , the wings are grasped at the wrist joints and ankles , and then the distance is measured between the tips of the longest primary feathers on each wing . To measure the wingspan of a bird , a live or freshly dead specimen is placed flat on its back , the wings are grasped at the wrist joints , ankles and the distance is measured between the tips of the longest primary feathers on each wing .