ILLINOIS AUDUBON SOCIETY 15 



Bird Migration and the Weather 



Just as the daily constitutional may become far more interesting by 

 acquiring a knowledge of the birds and making it a daily bird trip, so 

 the daily bird trip may become more interesting by having some definite 

 problem which requires for its solution the records of the daily trips. 

 Such a problem is involved when one attempts to determine what re- 

 lation there may be between bird migration activities and the weather. 

 Anyone so situated that he can make such daily trips may expect some 

 degree of success in attempting the solution of the problem for him- 

 self. Records should be made that show as complete a list as possible 

 of all the kinds of birds seen and an approximately accurate record of 

 the numbers of each of such species as are migratory. The more com- 

 plete the records, and the more accurate the correspondence between 

 the records of "first seen" and the actual first arrivals, the more con- 

 sistent will be the results obtained when one compares the weather 

 conditions that prevail at the times of great migration activity. It is 

 evident that the results would be confusing if there were actually ten 

 new arrivals in one night and only five of them were recorded the next 

 day and the others a day or two later, when very different weather con- 

 ditions might prevail. Cooperative effort in such a study has obvious 

 advantages. The combined results of several workers are quite sure 

 to be more complete than those of any one of them. 



An outline is here given of some of the results obtained from a 

 study of this kind, made in the vicinity of the University of Illinois dur- 

 ing the Spring migration periods of the years 1903-1917. The records 

 used are the combined results of the observations of various persons 

 and include the records of the classes in ornithology, additional records 

 of the instructors, and of other competent observers in the community. 

 The appearance of species not previously reported for the season is 

 taken as an evidence of migration, and the records usually show that the 

 appearance of any considerable number of these "firsts" at one time has 

 been accompanied by extensive movements among certain other migra- 

 tory species previously recorded. 



The average Spring migration season for the fifteen years has had 

 89 days, and the average number of "firsts" considered has been 119; 

 but theses have been so bunched that when we select for a season the 

 records which show the greatest number of "firsts," we find that, on 

 the average, 61 of them have been recorded on 9 days. The extremes 

 were in the season of 1907 when it took 14 days to record one half of 

 the "firsts," and in 1912 when one half of them were bunched in 5 days. 

 This lack of uniformity in distribution is still more apparent when we 

 examine the records of the last 30 days of each season, during which 

 three fifths of all the arrivals make their appearance. On the average, 

 73 "firsts" are recorded in these 30 days and 39 of them are bunched 

 on 4 or 5 days. Extremes occurred in 1915 in which it took 8 days to 

 record one half of the "firsts" of the last 30 days, and in the years 

 1909 and 1916 in each of which it took but 2 days. One half of all the 

 "firsts" of those 15 seasons of 30 days each were recorded on a total of 



