He says that in South Africa there is a scientist who has studied black eagles for more than twenty years. The male and female black eagle are completely identical in their external physical features, but through many years of observation, she became able to distinguish the male and female of a pair of black eagles flying together, from their attitude and position.
他說，南非有一科學家研究黑鵰廿幾年，由於黑鵰雌、雄身體特徵完全一樣，長久的觀察，使他可以由兩隻黑鵰飛行姿態、位置，辨認出雌、雄。