^"'^ me^"^] Tyler, Call-notes of Migrating Birds. 139 



wind (April 4, 1908). Weather, indeed, appears to have little 

 influence on the migration of birds, as evidenced by their call- 

 notes, except that on fair nights the birds evidently fly high; the 

 calls are fainter and appear to come from far away, whereas on 

 nights when the sky is overcast (or when it is raining) the birds 

 seem very near. 



In watching birds during the seasons of migration or in listening 

 to their call-notes night after night, it soon becomes apparent that, 

 quite irrespective of the weather, certain nights are chosen to move 

 northward or southward;, there is either a migration or there is not. 

 The birds appear to recognise the migration nights in advance as if 

 the individuals of one (or related) species possessed the knowledge 

 in common. My notes give a striking illustration of this point. 

 "On October 11, 1914, in the late afternoon when Mr. Walter 

 Faxon, Mr. Lewis Dexter, and I were crossing the Ipswich sand- 

 hills, Myrtle Warblers continually flew over our heads, all in a 

 southerly direction. In ten minutes we counted twenty birds, 

 flying at the height of a tall elm tree. We were standing among 

 the dunes about a quarter of a mile from the sea. To the south 

 was a small wood of pitch pines surrounded by sand, and as the 

 birds were flying toward these trees, and as they appeared to fly 

 lower as they approached them, we thought at first that the birds 

 were seeking a roosting place. But when we entered the wood, 

 we saw that, although the Warblers often dipped toward the tree- 

 tops in their flight over the wood, they did not alight, but continued 

 on toward the south. After watching the birds fly over for half 

 an hour in a steady, if rather straggling, procession, we felt certain 

 that they had begun a migration flight which they would keep up 

 all night. We first noticed the birds between half past four and 

 quarter to five, in broad daylight (sun set at 5.11). The birds 

 were rather widely separated from each other as a rule, but occa- 

 sionally one approached another and swooped at him. Once, 

 when a bird was attacked in this manner, he came down into a 

 thicket of bayberries, closely followed by his pursuer. The two 

 birds remained in the shrubs but a moment, however, before rising 

 and continuing their southerly flight. As the birds passed over 

 head, they gave their characteristic "tcheck," and almost as fre- 

 quently, the sibilant call heard most often when they take short 



