112 



weeds, the different kinds of grain being merely larger or more 

 important grasses.'^ 



That this change in food takes place is in itself very interest- 

 ing, but the explanation for it would be much more so. Beal 

 goes on to suggest an explanation which is very plausible, and 

 which would undoubtedly have received additional support, 

 had his studies been more intensive or had they included more 

 than the food. He states: *^The diagram on p. 38 shows in a 

 striking manner the increase of the animal food in early summer 

 — that is, in June. It is probable that the exhaustive labors 

 of reproduction call for a more exclusively animal diet in May 

 and June than does the strain of moulting in July and August. 

 There seems to be no other theory by which to explain the 

 decrease in the latter month, especially in view of the fact that 

 these are the months when grasshoppers abound. '^ 



In the present work, an effort has been made to study the 

 changes in the Redwing's food in the light of synchronous 

 changes in the environment and correlated changes in the 

 available food supply. Likewise, an attempt has been made 

 to determine changes which take place within the birds them- 

 selves, especially in connection with the alimentary canal and 

 the reproductive organs. Inasmuch as there is such a differ- 

 ence in the available food supply of the marsh and of the up- 

 lands, it is of prime importance always to bear in mind the 

 locaUty in which the birds have been feeding. In general, 

 most of the food of the migrating birds is secured on the up- 

 lands, and that of the resident birds, in the marsh. But those 

 migrants which are the first to arrive in the evening and the 

 last to leave in the morning, feed to a greater or less extent in 

 the marsh. As these are most easily collected, a considerable 

 number of the migrating birds will be shown in the table as 

 finding their food in the marsh, and allowances must be made 

 therefor. The normal difference between the food of migrating 

 and resident birds is so great that allowances should be made 

 also in applying BeaFs curves to the life history of individuals, 

 for his data probably include both migrating and resident 

 birds on the same date. The following table includes the 

 result of the studies made in Renwick Marsh. The nature of 



