44 RIDGWAY ORNITHOLOGICAL CLUB. 



For a long time I was unable to decide whether the sound was 

 vocal or mechanical, as it at first seemed as if the increase in volume 

 and pitch of the sound was due to the increased velocity of the 

 descent, especially so as the sound died away when he rose, but 

 I now believe it to be purely vocal. 



Their velocity at such times is very great, so great that should 

 the bird accidentally strike a branch he would not only be killed, 

 but undoubtedly torn to pieces. I can compare it to nothing but 

 the swoop of the Falcon, and I think that the velocity of the 

 hummer at such times at least equals that of the Falcon. The eye 

 cannot keep track of the bird at the lower part of the curve — with 

 some practice I was able to keep him in sight through all the rest 

 of the circle, but, as he came down faster and faster, I lost him, 

 only to spy him again when he had risen a short distance. 



I have watched quite a number this Spring and all of them 

 seem to go over the same course as nearly as possible. Some rise 

 much higher than others, the extreme height being some 400 feet 

 and the minimum 40 to 50 feet, with an average of about 200 feet. 

 The number of swoops per minute varies from two to ten (approx- 

 imately). 



I have three times seen $ of T. alexandri go through a similar 

 performance. Twice the $ was sitting on an exposed twig when 

 the $ swung back and forth before her, meanwhile giving vent to 

 a peculiar bee-like buzzing sound. This swing was nearly hori- 

 zontal and only three or four feet in extent. On the other occasion 

 the $ was sitting in the shelter of a mesquite, the $ rose 30 01-40 

 feet in the air, sweeping down again like T. costcz but, instead of 

 passing on overhead and thus completing the circle, he swung 

 back through an arc, reversing his direction at each end. 



The sound, like that of costce, increased as he descended and 

 died away again as he rose. It was not, however, quite as shrill 

 as with coslce, and as it became loudest it became tremulous, like 

 the tremolo of an organ. This tremulous quality proves its vocal 

 origin. As it was impossible to tell the species in its active motions 

 and as the note was new to me I carefully kept him in view until 

 he alighted, when I shot him. 



On June 23rd, I witnessed the swooping manoeuvre of T. 

 calliope. He did not rise far after his downward plunge, but re- 

 versed his direction, flying back over the same track as in the down- 

 ward swoop, then reversing again, he flew higher. He made but 

 two or three passes. 



