162 



THE OOLOGIST 



Fall Migration of the Olive-Backed 



Thrush, 1912. 



(Hylocichla Ustulata Swainsoni) 



By Paul G. Hawes, Stamford, Conn. 



"Pooorp - peenk - pue - pooorp." The 

 night voices fill the September air; 

 wierd, almost awesome are these 

 whistles of the migrating thrushes, 

 guided by some unknown power 

 through thousands of miles of space 

 to their winter home in the tropics. 

 It is thrilling indeed when one hears 

 the sound high in the air and far in 

 the distance. Gradually it comes 

 closer as the bird flies steadily south- 

 ward. As it passes, unseen, directly 

 over head, again the cry floats down 

 to earth and a fainter answering call 

 in the north, tells one of a companion 

 or perhaps a mate. Thus the voices 

 echo back and forth across the sky 

 from evening 'till early morn, vvhen 

 the birds drop down from the high 

 road of travel to feed and rest in the 

 friendly woods and thickets. I know 

 of many bird voices and calls, but 

 none of them could be used as a com- 

 parison, for the notes of the Olive- 

 backed Thrush are quite distinct from 

 those of any other bird that I am 

 familiar with. Not the metalic 

 "Peenk" of the migrating Bobolink 

 nor the sharp "peet peet" of the sand- 

 pipers, but a singular mellow and al- 

 most plaintive whistle, sweet-toned 

 and far reaching, seems best to de- 

 scribe the calls of this thrush. 



This fall, between September 5th, 

 and October 17th there passed a horde 

 of these birds, more than the writer 

 has ever seen before, over and 

 through the country about Stamford. 

 The migration started on September 

 Gth, when about fifty birds, compris- 

 ing two larger flocks than I had ever 

 noted, dropped down out of the sky 

 into a small patch of woodland about 

 5 A. M. I managed to secure two of 

 these birds which proved to be young 

 males. 



The appearance of these flocks 

 gave me the idea of studying and re- 

 cording the interesting points of the 

 migration as shown in the figures 1, 

 2, and 3. This idea was to mark out 

 a square upon the ground; six hun- 

 dred feet, being the length of its sides. 

 By this method one might note each 

 bird that passed through a corres- 

 ponding area of sky, this area being 

 directly above the square upon the 

 ground. Not only could the bird be 

 noted, but the exact direction could 

 be taken and easily recorded in the 

 figures. 



On the morning of the fifth, four 

 singles were noted and these, to- 

 gether with the two flocks, totals 

 about flfty-four specimens, noted be- 

 tween the hours of 5 A. M. and 7 A. M. 

 The singles were all flying several 

 hundred feet in the air, in a south- 

 westerly direction, none of them com- 

 ing down to rest. The two birds which 

 I took had nothing in their stomachs, 

 and the flocks began at once upon 

 the berries of the common Elder 

 (Sambucus Canadensis). 



The morning of September 10th 

 found me again at my "Bird Square" 

 before sun up, and this time, a flock 

 of twenty-flve (afterwards splitting in- 

 to two smaller onQs), three flocks of 

 ten birds each, and four singles were 

 noted in one hour. This total of 

 fifty-nine birds were seen in exactly 

 one half of the time that the fifty-four 

 were seen on September fifth. (Com- 

 pare Fig 1 and 2.) None of the birds 

 noted on the tenth came down, and 

 all of them were flying very high. 

 Notice that the temperature for 7 de- 

 grees lower on the tenth than on the 

 fifth and that the barometer was also 

 10-lOOth lower. 



September sixteenth found this ex- 

 traordinary bird movement at its 

 height. The temperature was eigh 

 teen degrees lower than on the fifth. 



