INTRODUCTION. 23 
Buntings, and the much less common Evening Grosbeak and Bohemian 
Waxwing. 
We may study the main features of migration to best advantage among 
those species in which the whole body of individuals swings northward and 
southward periodically and for long distances, at least 20° to 25° of latitude 
or 1,200 to 1,500 miles. Among these are representatives of the most diverse 
orders and families with many peculiar and exceptional cases, yet much 
general agreement as to the main facts. Some go openly, in immense flocks, 
by day and in fair weather, as the swallows, sandpipers and crows; others, 
like the cuckoos, flycatchers and rails, are commonly believed to go singly 
and at night, and they drop away so stealthily, even mysteriously, that this 
supposition seems justified. Many waterbirds, geese, ducks, and others, 
seem to wait for storms of wind or rain and to delight in making their long 
flights in or just before tempestuous weather. 
One of the older and seemingly well-grounded beliefs was that many of 
the smaller and presumably weaker migrants travelled entirely at night, 
partly to avoid the attacks of hawks and partly that they might rest and 
feed by day. The fact that multitudes of such birds do travel at night is 
undeniable, and perhaps the most marvelous demonstration of this is the 
discovery (first announced in October, 1880, by W. E. D. Scott) that this 
migration could be watched easily with a telescope trained on the face of the 
full moon within a few hours of the horizon. Yet the fact seems to have 
been very generally overlooked that night flying does not preclude day 
flying, and that millions of small birds might pass over our heads at midday 
and in fair weather, and yet be just as invisible as at midnight, provided they 
flew at the heights claimed for the nocturnal migrants. Similarly, the fact 
that birds appear by thousands about lighthouses and electric lights during 
cloudy and foggy nights carries not the slightest proof that the same species 
do not travel just as freely by day. Asa matter of fact we know that almost 
all the species killed at lighthouses do make long flights by day under favor- 
able conditions, and an examination of all the accessible evidence leads me 
to assert that most birds do not fly at night to avoid enemies or escape 
observation, but merely to take advantage of favorable conditions as yet but 
partially understood. Telescopic observations at night have shown many 
small birds flying at heights of from one to three miles, and even at a height 
of a mile most of the same birds would be entirely invisible to the unaided 
eye in a clear sky at noon. Moreover, telescopic observations by day—the 
telescope trained on the sun—have shown in at least two cases birds flying 
at great heights, far above the reach of our unaided eyesight, and in one of 
these cases the birds were migrating southward in enormous numbers. 
Different observers of nocturnal migration, using different instruments 
under similar conditions (that is always against the face of the full moon) 
have recorded birds migrating at heights estimated all the way from 600 feet 
to 15,100 feet, and moving at all speeds from nearly stationary up to 134 
miles per hour, with an average of sixty-seven miles per hour for small birds 
of ordinary powers of flight. 
J have not the least desire to belittle the discoveries of these pioneer 
observers, or to cast any reflection on their honesty of purpose or the accuracy 
of their records, yet I am free to say that until we have very many more 
observations in corroboration of these I cannot but doubt that any of our 
birds, large or small, at any height or under any circumstances, attains a 
speed even approximating 100 miles an hour. At a height of little more 
than three miles the density of the atmosphere is only half that at the sea- 
