216 



Carpenter, Height of Migrating Birds. 



TAuk 

 L April 



Table II. 

 Birds migrating on the night of October 10, 1905, three days 

 before full moon. Weather clear. Wind west, 12 miles an hour. 

 Temperature at 9 P. m. 48° F. 



Table I shows that on May 19-20 no birds were one-half mile 

 above the ground, and one was as low as 1200 feet. On October 

 10, however, as can be seen from Table II, a single bird was slightly 

 over a mile high. Three others ranged between one-half and one 

 mile, while the remaining five were below one-half mile, two being 

 at an elevation of 1400 feet only. It should be noted that the 

 position of the telescopes did not permit the measurement of birds 

 which may have been lower than the point marked E in the diagram, 

 which point on May 19-20 varied between 550 and 1100 feet from 

 the ground, and on October 10 between 750 and 800 feet. As 

 the diagram shows, the area of simultaneous observation (E C D) 

 becomes narrower as the point E is approached, and as a con- 

 sequence the chances of birds appearing therein are correspondingly 

 decreased. 



The conditions, then, were most favorable for the detection of 

 the uppermost birds, and it seems probable that the majority were 

 considerably below the highest records obtained. On both nights 

 the calls of birds apparently not far overhead were frequently 

 heard. Furthermore, Professor Stebbins has determined the upper 

 limit of over half of those birds seen by one of the observers only 

 on October 10, and shows that these must have been below 1600 

 feet. In the diagram it will be seen that the area of observation of 

 each telescope has been divided into halves by dotted lines. If 

 the observer at .4 saw a bird, not seen from B, against the right 

 half of the moon that bird must have been in the area .4 F E. 



