CHESTNUT-SIDED WARBLER 373 



Food. — The chestnut-sided warbler is ahnost wholly insectivorous, 

 though it has been known to eat a few seeds or berries when hard- 

 pressed for food. Its foraging range is between the ground and the 

 tops of small trees, or in the lower branches of some of the larger 

 trees ; but mainly it gleans through the foliage of shrubbery or low 

 plants, seldom seeking its food on the ground. 



The insects mentioned under the food of the young are all doubtless 

 eaten regularly by the adults; when securing tent caterpillar webs 

 in nest building, it probably does not object to eating a few of the 

 smaller caterpillars but the large, hairy ones may be refused. Spiders 

 are eaten to some extent. No very comprehensive study of the food 

 seems to have been made, but Forbush (1907) makes this general 

 statement : "The food of the Chestnut-sided Warbler is such that the 

 bird must be exceedingly useful in woodland and shrubbery, and in 

 orchard and shade trees as well, whenever it frequents them. It is 

 probable that at times it destroys considerable numbers of parasitic 

 hymenoptera, as it is rather expert as a flycatcher; but it is very de- 

 structive to many injurious beetles and caterpillars, being one of the 

 most active consumers of leaf-eating insects. Small borers or bark 

 beetles, plant bugs and plant lice, leaf hoppers, ants, and aphids are 

 eaten." 



Professor Aughey (1878) reports that a stomach examined in Ne- 

 braska contained 17 locusts and 21 other insects. F. H. King (1883) , 

 reporting for Wisconsin, mentions one eating a small grasshopper 

 and canker worms that were feeding on oaks, hazel, hickory, plum, 

 cherry, apple, pear, and currant. Du Bois tells me of one he watched 

 gleaning its food in an elm tree: "In order to secure insects from 

 the under side of an elm leaf, he hovered like a hummingbird at a 

 flower, and thus picked the food from the leaf while poised in the 

 air." Forbush (Chapman, 1907) writes: 



A Chestnut-sided Warbler was seen to capture and eat, in fourteen minutes, 

 twenty-two gipsy caterpillars, that were positively identified, and other insects 

 that could not be seen plainly were taken during that time. * * * ^ Chest- 

 nut-sided Warbler took twenty-eight browntail caterpillars in about twelve 

 minutes. When we consider that the short hairs on the posterior parts of 

 this caterpillar are barbed like the quills of a porcupine and will penetrate 

 the human skin, causing excessive irritation and painful eruptions, we may well 

 wonder if the little bird lived to repeat this performance. But many small birds 

 eat these caterpillars at a time when probably the noxious hairs have not fully 

 developed, and others seem to have learned to divest the larger caterpillars of 

 their hairs by beating and shaking their prey and thus loosening the hairs, 

 which are shed as the porcupine sheds its quills. The insect is then eaten with 

 impunity and even fed to the young birds. 



Audubon (1841) tells us that five chestnut-sided warblers, taken dur- 

 ing a light fall of snow in May, had eaten nothing but gi^ass seed and 

 spiders. 



981S73— 53 25 



