48 FOOD HABITS OF THE GEOSBEAKS. 



tato beetle in many patches it patrolled. Mr. W. F. Bundy,« who 

 was among the earliest to write upon the subject, says : 



I noticed last summer that great numbers of the Colorado potato beetles were 

 destroyed by the rosebreasted grosbeak. * * * They were so abundant in 

 this region [Jefferson, Wis.] * * * as to hold in check the vast army of 

 these ravagers of the potato crop. 



The beetles are attacked as soon as they emerge from their winter 

 quarters, according to Mr. J. S. Cook,^ of northern Illinois, who says : 



I have seen them so gorge themselves with these beetles that they were 

 scarcely able to tly. I have investigated in the spring, when the beetles first 

 came out of the ground, and was unable to find a single one after following 

 these birds. 



Further testimony to the value of the bird is given by Prof. 

 F. E. L. Beal," who watched the grosbeaks and their young' feeding 

 upon the potato bugs in his garden at Ames, Iowa : 



When a careful inspection was made a few days later not a beetle, old or 

 young, could be found ; the birds had swept them from the field and saved the 

 potatoes. 



Comparison of the dates of the first appearance of the Colorado 

 beetle with the earliest records when the rose-breasted grosbeak fed 

 upon it shows that from six to ten years passed before the bird com- 

 monly began to prey upon the insect. Even after the lapse of so 

 much time it was one of the first enemies of the beetle noted and by 

 far the most important among birds. 



The results of stomach examinations fully corroborate the testi- 

 mony of field observers as to the extent to which the rosebreast 

 feeds upon this beetle. Forty-three, or almost one-fourth of the birds 

 examined, fed upon the potato beetle to such an extent that the in- 

 sect makes up 9.05 percent of the subsistence of the entire number 

 and nearly 35 percent of tliat of the individuals eating it. The 

 significance of these figures will be better appreciated when it is 

 considered that the potato beetle probably was not obtainable by 

 many of the grosbeaks, and furthermore, that it is very unusual for 

 birds to prey so extensively upon a single kind of insect, or even on 

 the species collectively of a whole group. Such concentration of 

 attack of a common bird upon a single species of insect, however 

 numerous, can not but have a restraining influence on its numbers. 

 The beetle is fed upon from May to September and both larvae and 

 adults are devoured, 10 to 14 being found in single stomachs. By 

 feeding upon the larvae the rosebreast directly benefits the potato 

 plants, and by destroying adults the increase of the species is checked. 



" Am. Nat., IX, 1875, p. 375.. 



» Trans. 111. Hort. Soc, 37 (1903), 1904, pp. 331-332, 



^ U. S. Dept. Agr., Farmers' Bui. 54, 1904, p. 35. 



