24 CIRCULAR 363, U. S. DEPARTMENT OF AGRICULTURE 
The faculty that enables these birds to point their course accurately 
over vast expanses of land and water may for want of a better term be 
called a ‘‘sense of direction.’”” Man recognizes this sense in himself, 
though usually it is imperfect and frequently at fault. Nevertheless 
the facility with which experienced hunters and woodsmen locate tiny 
camps or other points in forested or mountainous country, frequently 
cloaked by darkness or fog, with all recognizable landmarks obliterated 
seems due to this faculty. Ability to travel with precision over 
unmarked trails is not limited either to birds or to man. It is like- 
wise possessed by many mammals as well as by some insects and 
fishes, the well-known migrations of the salmon (Oncorhynchus) and 
the eel (Anguilla) being notable examples. 
Ability to follow a more or less definite course to a definite goal is 
evidently part of an inherited faculty. Both the path and the goal 
must have been determined either when the habit originated or in the 
course of its subsequent evolution. The theory is sometimes advanced 
that the older and more experienced birds lead the way, showing the 
route to their younger companions. This explanation may be 
acceptable for some species, but not for those in which adults and the 
young migrate at different times. The young cowbird that is reared 
by foster parents flocks with others of its kind when grown and in many 
cases can hardly be said to have adult guidance in migration. An 
inherited migratory instinct with a definite sense of the goal to be 
reached and the route to be followed must be attributed to these 
birds. 
It is known, however, that birds possess wonderful vision. If they 
also have retentive memories, subsequent trips over the route may well 
be steered in part by recognizable landmarks. The arguments against 
the theory of vision and memory are chiefly that much migration takes 
place at night and that great stretches of the open sea are crossed 
without hesitation. Nevertheless, the nights are rarely so dark that 
all terrestrial objects are totally obscured, and such features as 
coast lines and rivers are just those that are most likely to be seen 
in the faintest light, particularly by the acute vision of a bird and 
from its aerial points of observation. But some birds fly unerringly 
through the densest fog. Members of the Biological Survey, pro- 
ceeding by steamer from the island of Unalaska to Bogoslof Island in 
Bering Sea through a fog that was so heavy as to make invisible 
every object beyond a hundred yards, recorded the fact that flocks of 
murres, returning to Bogoslof, after quests for food, broke through the 
wall of fog astern, flew by the vessel, and disappeared into the mists 
ahead. The ship was heading direct for the island by the use of com- 
pass and chart, but its course was no more sure than that of the 
birds. 
Some investigators have asserted that the sense of direction has 
its seat in the ears or nasal passages and thus that the bird is enabled 
to identify air currents and other phenomena. It has been found that 
disturbance of the columella, or the semicircular canals of the inner 
ear, will destroy the homing instinct of the racing pigeon, but experi- 
ments in the form of delicate operations, or closing the ears with wax, 
prove such a serious shock to the sensitive nervous system of the bird 
that they cannot be considered as affording conclusive evidence. 
Several years ago careful studies were made of the homing instinct 
of the sooty and noddy terns (Sterna fuscata and Anotis stolidus), 
