Vol. XXXIII 1 



1916 



J Tyler, Call-notes of Migrating Birds. 133 



under way. Every night early in August, or even late in July, we 

 may hear hundreds of bird-calls from nocturnal migrants, as they 

 pass over head southward in the quiet and darkness. 



For the past few years I have been much entertained and fasci- 

 nated by listening from my sleeping-porch to the notes of these 

 migrating birds. Being practically out-of-doors, my attention 

 was naturally drawn to the frequent clear-cut " chips " and whistles ; 

 they were so distinct and sharp, and apparently so near, but withal 

 so mysterious and baffling as to arouse my curiosity. One is at 

 first impressed by the fact that most of the call-notes which he 

 hears over and over again, often in great variety, are notes which he 

 has never heard before, and consequently can ascribe to no known 

 bird. Again, after a few jears of observing, one realises that each 

 year the notes (at first strange and unfamiliar, but finally perfectly 

 recognisable from one another) occur in a definite order; as the 

 season advances, one note after another makes its appearance, 

 becomes frequent, and later drops out to be heard no more. Here 

 then is a basis to work on. From the known times of migration 

 of certain birds, is it not possible to identify the authors of some of 

 the common nocturnal notes, or at least to surmise their identity 

 with a fair degree of certainty? 



During the very first nights of the autumnal migration (July 

 29 is my earliest date) the notes are always the same, — high and 

 sibilant, with a sharp, ringing quality. The sound is represented 

 so closely by the letters "ks" that I have called this note the "x" 

 note. This call contains no vowel sound, — it is so short, indeed, 

 that it cannot contain one — it is over almost as soon as it begins. 

 In spite of the necessarily vague idea one receives from reading a 

 description of so indefinite and fleeting a sound as a bird's "chip," 

 this note is perfectly recognisable; after one has once become 

 familiar with it, he can distinguish it readily even when it occurs, 

 later in the season, with many other calls. The " x" note, as I have 

 said, is the fii'st note heard in the autumnal migration. It is 

 commonest during the first half of August, when it is heard on 

 favorable migration nights almost incessantly, evidently from 

 thousands of birds, and it disappears soon after the first of Septem- 

 ber. From these facts we might deduce, that the species which 

 uses the "x" note as a migration call is a nocturnal migrant which 



