Ranvaud R D, Gasparotto O C, Britto L R
Departamento de Fisiologia e Biofísica, Universidade de São Paulo, Brasil.
Braz J Med Biol Res. 1996 Oct;29(10):1341-7.
The sun is known to guide homing pigeons as a priority cue. The literature indicates that under total overcast conditions pigeons rely on a backup mechanism akin to the magnetic inclination compass for which there is much laboratory evidence in migratory birds. Total overcast conditions are not favorable for orientation research in the State of São Paulo, Brazil. The orientation of homing pigeons raised near the tropic of Capricorn was therefore observed around the time of the December solstice, when the sun culminated directly overhead, with a consequent interruption of the sun compass for a short time every day. In these experiments, carried out between 1981 and 1993, local geomagnetic field inclination was -25 degrees to -29 degrees 30', so that a functioning magnetic inclination compass should have been available to the birds. Whereas the birds released with sun to zenith angles between 10 degrees and 30 degrees were well oriented, both in the morning (99 vanishing bearings) and in the afternoon (143 vanishing bearings), those released with the sun less than 5 degrees away from the zenith showed random orientation (105 vanishing bearings), with no evidence of an alternative magnetic compass mechanism.
众所周知，太阳是引导信鸽归巢的首要线索。文献表明，在完全阴天的条件下，鸽子依靠一种类似于磁倾角罗盘的备用机制，候鸟身上有很多关于这种机制的实验室证据。在巴西圣保罗州，完全阴天的条件不利于进行定向研究。因此，在12月冬至前后，当太阳直射头顶，导致太阳罗盘每天短时间中断时，观察了在南回归线附近饲养的信鸽的定向情况。在1981年至1993年进行的这些实验中，当地地磁场倾角为-25度至-29度30分，这样鸟类应该可以使用正常运行的磁倾角罗盘。在早晨（99个消失方向）和下午（143个消失方向），太阳天顶角在10度至30度之间放飞的鸟类定向良好，而太阳离天顶不到5度时放飞的鸟类则表现出随机定向（105个消失方向），没有证据表明存在替代磁罗盘机制。
