Keeton W T, Gobert A
Proc Natl Acad Sci U S A. 1970 Apr;65(4):853-6. doi: 10.1073/pnas.65.4.853.
Untrained homing pigeons released on sunny days oriented homeward regardless of the direction of the release site from the loft. Similar pigeons released under total overcast vanished randomly, whereas experienced birds released on the same days at the same sites oriented homeward. Apparently untrained pigeons require the sun for orientation but experienced pigeons do not.
在晴天放飞的未经训练的信鸽会朝着家的方向飞行，无论放飞地点相对于鸽舍的方向如何。在完全阴天的情况下放飞的类似鸽子则随机乱飞，而在同一天同一地点放飞的有经验的鸽子会朝着家的方向飞行。显然，未经训练的鸽子需要太阳来定向，而有经验的鸽子则不需要。
