164 SEA-BIRDS 



sense) ; by dead reckoning, probably in terms of flying-time rather 

 than distance covered; by observing the sun and stars and their position 

 in relation to the horizon. They may exploit other signs, such as the 

 set of the currents, temperatures, and the presence of animals of their 

 own or other kinds. We know that birds can make the mistakes that 

 human navigators make, such as getting adrift and wrecked. And 

 we know that they can, by instinctive orientation and navigation, 

 without instruments, do things that humans cannot do. 

 That is the present state of our knowledge. 



