82 



ORNITHOLOGIST 



[Vol. 10-No. 6 



portional to the number and excellence of the 

 observers. It also secras probable that to the 

 northeastward the limit of the wave was at Madi- 

 son, Wis., thence up the Mi.ssissippi to St. Paul. 

 There is a striking .similarity in the species whicli 

 are reported from the stations between St. Paul 

 and St. Louis, with this difference that while the 

 northern stations report the first males, St. Louis 

 reports first females and bulk. Nearly one-half 

 of all the records is made up of notes on the Bal- 

 timore and Orchard Orioles, Rose-breasted Gros- 

 beak, Indigo Bunting, Bobolink, Catbird, and 

 Ked-headed Woodpecker. No less than twelve 

 records are sent of the Baltimore Orioles from si.\ 

 different States. We would look in vain, how- 

 ever, for these species in tlie notes from Manitoba. 

 There we have a great bird wave, it is true, but 

 the species are totally different, being those like 

 Ycllow-rumped Warbler and the White-crowned 

 Sparrow, which passed through the central dis- 

 trict some weeks before. As in the case of the 

 great wave which we studied in March, there are 

 about half as many notes reported May 6th, on 

 the day after the wave has passed, but the notes 

 come from tlie same places as the day previous, 

 and are "ones" and "twos," indicating that they 

 are species which arrived tlie day before but were 

 not noted. The only exception to this is in north- 

 eastern Wisconsin, where tlie notes would indi- 

 cate a lai'ge local wave, but though it is now too 

 late for verification, it would seem more likely 

 that the observer was unable to be in the field on 

 May 5th and did not see the an-ivals until the 

 next day. 



Now comes a north wind [icriod. The low 

 area has passed east of our district and is followed 

 by colder and at the same time cloudier weather. 

 During May 7th and 8lli there is not a record out 

 of the whole eighty with a S. S.E. or S.W. wind. 

 But the birds do not stop; there seems to have 

 been a regular though not rapid advance, there 

 being on the night of May 6th, thirtj'-six records, 

 every one with N. or N.W. wind and cloudy sky. 

 Were it for a .single night only, we might be in- 

 clined to call it a mistake of the observers, but 

 the whole eighty records for the two nights can- 

 not be wrong, and we are compelled to believe 

 that during the latter part of migration, there is 

 no night so unfavorable, but that more or less 

 migration takes place. 



On the night previous to May 9th, we find the 

 least migration of the seven nights we are study- 

 ing. A low area had developed two days before 

 in Manitoba, passed across Lake Superior and be- 

 came central at Lake Huron, May 8th, at lip. 

 m. It had produced a great rise in temperature. 



5° to 11°, in the Upper Mississippi Valley, so 

 much so as to make this section actually warmer 

 than the middle portion. LaCros.se 70°, St. Louis 

 6.5°, Omaha 69°, Little Rock 66°, Bismarck 55°, 

 Ft. Elliott 53°, but the area passed so far north, 

 that the south wind it caused was of too short 

 duration to start migration. The notes given are 

 those from places where the southerly winds 

 were felt, principally in northwestern Illinois, 

 with the exception of a batch of records from 

 central Iowa, where a northwest wind prevailed. 

 The whole of our district was clear, and the 

 average barometer about 30.0 inches. 



In western Neliraska and eastern Colorado, it 

 is found that the barometer, though Iiigh, is fall- 

 ing and during the day time of May 9tli it falls 

 rapidly. At Yankton, during the sixteen hours 

 previous to 11 p. m.. May 9th, the pressure falls 

 .34 inches to 39.74 inches. Thus the low area 

 developed right in our district, and its influence 

 was speedily felt, bringing on southerly winds, 

 and sending northward almost the last great wave 

 of the Spring migration. The temperature did 

 not vary much from that of the night before, ex- 

 cept to rise a little in the immediate vicinity of 

 the low area and to fall at La Crosse and north- 

 eastward; sky mostly clear; wind variable, the 

 low area not having 3'et had time to fully affect 

 the winds, but every one of the records conies 

 from places where the winds were southerly, and 

 consequently from the cloudy places; so that, 

 although the larger part of the L^pper Mississippi 

 is clear, the cloudy records form 73 per cent, of 

 the whole number. Another thing is noticeable, 

 that notwithstanding the sky was cloudy yet the 

 dew point was many degrees below the tempera- 

 ture, showing that the air was very dry. While 

 the average of the difference between the temper- 

 ature and dew point of the records of May 5th, 

 is only four degrees, with a range from 0° to 8", 

 that is the air was almost fully saturated with 

 moisture; the records of May 10th show an aver- 

 age difference of fifteen degrees, with a range 

 from 11° to 33°. Thus we see that the humidity 

 of the atmosphere has little or no effect on migra- 

 tion, and we can leave that out of future records. 



This wave of the night of May 9tli, like the 

 one five da3's before, is an extended one. Along 

 the western shores of Lake Michigan, where the 

 weather has been cold and disagreeable for the 

 four days previous, it is most strongly felt. 

 Then there is little or nothing until we cross ilie 

 Mississippi. Here from Keokuk to Moorhead, the 

 night has been a time of great activity, even ex- 

 tending • southwest to southern Nebraska and 

 Kansas. No notes are sent from southern Da- 

 kota, and it is probable that almost no migration 



