123 



Food during the Fall Migration. — By the last week in Oc- 

 tober the migration is well under way, and the Redwings 

 spend very little time in the marsh. The food is taken 

 entirely from the uplands, and is practically 100 per cent 

 vegetable; it is composed chiefly of the seeds of foxtail grass 

 and ragweed, with a little grain (corn, wheat, and oats) inter- 

 spersed. This diet continues throughout the migrating period, 

 which ends about the middle of November. 



Such are the changes occurring — changes which pass through 

 all stages from a strictly herbivorous to a totally insectivorous 

 diet, and which must demand an exceptional adaptability as 

 well as a most generahzed structure. In conclusion, it may 

 be stated that the Redwings feed upon whatever is most avail 

 able; that during the migrating periods of spring and fall 

 they obtain their food upon the uplands, where the seeds of 

 foxtail grass and ragweed are most abundant; that during the 

 breeding season they obtain their food in the marsh, where 

 only animal food is available; that here their food is limited 

 only by their powers of capture, and varies with the species 

 predominating in the marsh. 



Correlation between Changes in Food and Changes 

 IN Structure of Stomach. 



Along with the change in diet from seeds to insects and 

 from insects to seeds, there is a corresponding change in 

 the nature of the gizzard. The comparatively soft-bodied 

 insects do not require the muscular strength that is neces- 

 sary to grind the hard seeds, so that with the decrease in 

 the amount of vegetable food eaten, there is a corresponding 

 degeneration in the musculature of the ventriculus. This is 

 well shown in Plate XX, fig. 2, where the stomachs of a migrat- 

 ing bird and a resident bird, taken on the same day, are 

 opposed {B and C). The migrant had not yet begun its 

 insectivorous diet, whereas the resident had been feeding 

 upon insects for at least a month. A similar difference is 

 shown between the stomachs of the two resident birds taken, 

 one at the time of first establishment in the marsh, and the 

 other after a month's residence (A and B). 



9 



