21 



That this was the culmination is easily seen from the records, which 

 fell from seventy-three notes on the 24th to but seventeen the next day. 



Let us now calculate the average conditions under which birds were 

 migrating during these seven days. A few more than three hundred 

 records of < firsts 7 were contributed for these seven days, and the tem- 

 perature at which the species were migrating is found to be as follows : 

 25°, one record (a Goose, in more senses than one) ; 29°, a cousin to the 

 last; 31°, eighteen firsts; 33°, twelve firsts; 35°, eleven firsts; 37°, 

 forty firsts ; 39°, forty-one firsts ; 41°, fifty-two firsts ; 43°, sixteen 

 firsts ; 45°, twenty-five firsts; 47°, five firsts; 49°, seventeen firsts; 51°, 

 nine firsts. Thus it will be seen that the favorite temperature for mi- 

 gration of "birds of the first wave" ranges from 37° to 41° Fahrenheit. 



In cloudy weather there were 143 records; in clear weather 101, or 

 exactly 60 per cent, cloudy, to 40 per cent, clear. 



With reference to the wind, it has been found that with the wind 

 north there were 29 records; NE., 31; E., 12; SE., 75; S., 23; SW., 

 27 ; W., 39 ; and NW., 9. It will be noticed that the most unfavorable 

 winds, namely, the E. and NW., are directly opposite those winds 

 which have the greatest number of records. Combining, we have for 

 E. and W., 51 records; for NW,, K, and JS T E., 69; and for SE., S., and 

 and SW., 125 records, showing how greatly the birds prefer a southerly 

 wind to help them on their journey. 



The effect of barometric pressure will appear from the following 

 statement : March 19 there were 24 records with an average pressure 

 of 30 inches; March 20, 35 records at 30.04 inches; March 21, 43 records 

 at 30.24 inches ; the 22d, 82 records at 30.15 inches ; the 23d, 45 records 

 at 29.80 inches ; the 24th, 73 records at 29.85 ; and the 25th, 17 records 

 at 29.86 inches. These give an average of exactly 30 inches, or the 

 normal pressure ; but it must be remembered that the great wave of 

 the 22d began when the pressure was very high and took place on a 

 falling barometer. It is probable that a large number of observations 

 taken throughout the season would give from 29.93 to 29.95 as the 

 average pressure at which most birds migrate. 



The above study of the influence of atmospheric conditions upon mi- 

 gration pertains to a single week in March, when the first wave was 

 passing over the Upper Mississippi Valley. A similar study will now 

 be made for a week in May, just before the close of migration for the 

 spring. The seven days from May 4 to May 10, 1884, have been chosen. 

 This brief period includes two warm waves and an interim of inde- 

 terminate nature. Naturally, the birds were migrating under very dif- 

 ferent conditions, and, as a result, a very different set of birds was con- 

 cerned. One may look in vain for notes on Ducks, Geese, Eobins, and 

 other early species. In their stead the brilliantly- colored Orioles, Gros- 

 beaks, Indigos, and Tanagers will be found. In the place of the frost 

 and cold of March, there is a summer temperature with frostless nights, 

 and swarms of insects are ready for the Warblers, Yireos, and Fly- 



