30 FOOD OF WARBLERS 



benefit and must always die without issue, even if they are not 

 eaten by birds. 



Birds eat not only the useful primary parasites but the injur- 

 ious secondary parasites that feed on primary parasites. Hence it 

 is questionable whether birds ever do much harm by destroying 

 parasitic hymenoptera, except by some unlucky accident. What- 

 ever injury they may do in this way is probably offset by their 

 destruction of injurious ants. Caddice flies and May flies are eaten 

 by Warblers. 



In addition to the insect food, some spiders, myriapods, and 

 snails are taken. Spiders are useful creatures, but if one will go 

 out into the woods and fields some dewy or foggy morning in fall 

 and observe how spiders' webs cover the fields, how they drape 

 the trees, and net the shrubbery, he will see how essential it is that 

 they be held in check lest a spider-plague overwhelm the land. 



Dr. Judd tells us that he found that ninety-six per cent, of 

 the food in the stomach contents of fifty-three Warblers taken on a 

 Maryland farm, consisted of insects, and that the arboreal Warb- 

 lers, other than the Myrtle Warbler are almost purely insectivor- 

 ous. Still some Warblers are able to subsist for a brief time on 

 vegetable food mainly. 



Audubon tells us that in May, 1808, during a light fall of snow 

 in Pennsylvania, he took five Chestnut-sided Warblers that had 

 eaten nothing but grass seeds and a few small spiders. Occasion- 

 ally small seeds or remains of wild berries are found in the 

 stomachs of Warblers, more particularly those of the ground-fre- 

 quenting species; but I have examined the digestive tract of Warb- 

 lers taken in the height of the berry season and found only insects 

 and spiders. The Myrtle Warbler, that hardy little bird that so 

 often winters in the north, eats very freely of the fruits of the 

 bayberry, waxberry or myrtle, and cedar : remains of grapes are some- 

 times found in their stomachs and small seeds are not disdained. 

 The Pine Warbler is said to feed on the seed of pine trees in 

 winter, and I have seen it eat suet almost as freely as does the Chick- 

 adee. 



On the whole, however, Dr. Judd rightly regards the Warblers 

 as insectivorous, and the value to man of those species that nest 

 in or near an orchard or shade trees is not likely to be overesti- 

 mated. 



The enormous number of insects that breeding Warblers must 

 secure to feed their young may be inferred from the fact that 



