HOW BIRDS MIGRATE 
53 
warm weather, Tree Swallows have been induced to travel northward 
and appear near New York City in numbers late in December. 
And now we ask the question to which any consideration of the 
phenomena of migration inevitably leads, “How do birds find their way?” 
What faculty directs them over thousands of miles of land and water 
through the darkness of the night with a regularity and accuracy that 
brings them to the same locality, even the same nest-site, on essentially 
the same date year after year? 
Granted that in birds, sight, hearing, and the power of association 
are exceptionally developed; that the chirping and calling of night 
migrants is an effective means of holding them to the main traveled 
way; that diurnal migrants are guided by prominent topographical 
features; still something far more potent than eye, ear, and memory 
is evidently required to lead birds over journeys where landmarks are 
wanting. 
While at sea on May 24, 1905, a Curlew ( Numenius sp.) boarded 
the steamer when we were 140 miles south of Fastnet Light. While 
photographing the bird, I alarmed it, when it took wing and headed 
for Ireland with as much confidence as though land had been visible, 
and was soon far beyond us. There was here no established line of 
flight in which to join, no evident external guiding influence; never- 
theless the bird set its course without hesitation. 
Terns, Murres, and other sea-birds go out to feed and return to 
their breeding-grounds through dense fog and with unfailing precision. 
Tropic-birds reach Bermuda, 600 miles from the nearest land, regularly 
each spring; Turnstones and Pacific Golden Plover travel twice each 
year over at least 2,000 miles of water in their journey to and from 
Hawaii. The Eastern Golden Plover strikes boldly out over the Atlantic 
bound from Nova Scotia to the Lesser Antilles; vast numbers of birds 
of many species cross the Gulf of Mexico, others fly from Jamaica to 
South America. 
This power of ‘distant orientation’ is apparently only to be explained 
through the bird’s possession of a ‘homing instinct’ or ‘sense of direc- 
tion’ which, when the impulse to migrate is active, automatically 
induces them to follow a certain route. 
The experiments of Reynaud (’00) and others with Homing Pigeons 
appear to have definitely established the existence of the sense of 
direction in this species, and more recently Watson (’09) has demon- 
strated in a most noteworthy manner its evident possession by Sooty 
and Noddy Terns. Among other tests, Reynaud transported five 
Pigeons, under the influence of chloroform, from Orleans to Evreux, 
France, a locality which they had not visited before. Two days later, 
having evidently recovered from the effects of the drug, they were 
released and all returned to Orleans. While the senses of sight, smell, 
taste, touch, and hearing were not functional during the time when 
the birds were under the influence of chloroform, Reynaud expresses 
his belief that “the sense of direction, on the contrary, whose action 
