145 



the stations during the same night, while the present wave occupied 

 two nights. For the next three days there were six notes from the Up- 

 per Mississippi Valley, which probably belong to this wave, though the 

 next two nights after the maximum were also warm and the birds very 

 likely did some migrating. These six do not indicate any advance be- 

 yond previous records, but are the filling in from stations in the rear 

 which had not before reported. 



Another wave occurred on the night of May 17, but all the notes re- 

 ceived on Kingbirds were made the previous day, which was also warm. 

 These records mark the arrival of the bulk at latitude 43° in Wisconsin, 

 and of the first at latitude 46° 33' in Minnesota, while — and the fact 

 is significant — it marked, as it should, the last transients seen at Saint 

 Louis, for certainly all lasts should be seen just before the maximum of 

 a warm wave. 



But few waves remain in which the Kingbird is concerned. One on 

 May 20 brought the bulk to latitude 43° 48' and 46° 33' in Minnesota, 

 and the first to latitude 46° 58' in Dakota, and lastly, on June 3, the 

 first appeared at Oak Point, Manitoba (latitude 50° 30'). To recapitu- 

 late, 76 observations were contributed on the movements of the King- 

 bird. Of these, 12 were made on the day before the maximum ; 10 the day 

 after the maximum; 9 exactly at the minimum, that is, when the polar 

 wave was at its height; 4 are evidently mistakes in identification, and 

 8 occurred at intermediate times when there was no decided wave either 

 cold or warm. This leaves 33 notes which agree exactly with the max- 

 imum of the warm waves. It is perfectly natural that when a warm 

 period is gradually increasing the birds should be influenced by it before 

 it reaches the maximum, so that the first 12 records spoken of may be 

 considered correct. Omitting the four mistakes, 72 records remain, of 

 which 11 per cent, are indeterminate, 28 per cent, do not agree with 

 the waves, and 61 per cent, agree exactly. 



Considering the lack of experience in noting migration on the part of 

 most of the observers, this is a very creditable showing. 



The average speed at which the Kingbird migrates has been calcu- 

 lated in the light of the above-mentioned cold and warm waves. It has 

 been assumed that no movement took place during the nights of pro- 

 nounced cold waves, and also that none occurred until at least the day 

 before the maximum, with the exception of the indeterminate times on 

 which there were notes. The record began at latitude 31° 52' in Mis- 

 sissippi March 31, and ended at latitude 59° 30' in Manitoba June 

 3. The species thus passed over 1,286 miles in sixty-four days, which 

 gives an average of twenty miles a day. Subtracting the nights of 

 no movement, but retaining all the nights on which there was any 

 possibility of movement, we find that there were thirty-two nights on 

 which migration might have taken place, which would give an aver- 

 age of forty miles a night. That the above estimate of the number of 

 non-movement nights is not too high may be seen from the records at 

 7365— Bull 2 10 



