EASTERN YELLOW WARBLER 171 



below. Old and young birds are now very much alike, often prac- 

 tically indistinguishable, except for the worn juvenal wings and tail. 



Adults have a complete postnuptial molt in July before or while 

 they migrate and a partial prenuptial molt, as in the young bird, 

 before they arrive in the spring. In El Salvador, according to Dickey 

 and van Rossem (1938), "both adults and young of the year were in 

 complete fall (postnuptial) plumage by the time they arrived. * * * 

 An adult male taken April 10 is in the midst of the spring (prenup- 

 tial) molt and presents an extremely ragged appearance. Another, 

 collected on April 24, has entirely finished this molt." 



In both adult male and female plumages the colors are richer and 

 the streakings below heavier than in the young bird, but the female 

 is always duller in color and the streaking is less prominent or en- 

 tirely missing. 



Food. — Edward H. Forbush (1907) writes of the food of the eastern 

 yellow warbler in Massachusetts : 



It would be hard to find a summer bird more useful among tbe shade trees or 

 in the orchard and small-fruit garden than this species. Almost entirely in- 

 sectivorous, it feeds on many of the greatest pests that attack our fruit trees, 

 vines and berry bushes. Whenever the caterpillars of which it is fond are 

 plentiful, they form about two-thirds of its food. It is destructive to the small 

 caterpillars of the gipsy moth and the brown-tail moth, and is ordinately 

 fond of cankerworms and other measuring worms. Tent caterpillars are com- 

 monly eaten. Small bark beetles and boring beetle are eaten, among them 

 the imago of the currant borer. Weevils are greedily taken. A few useful 

 beetles are sacrificed; among them ground beetles, soldier beetles, and small 

 scavenger beetles. The Yellow Warbler has some expertness as a flycatcher 

 among the branches, and seizes small moths, like the coddling moth, with ease, 

 but apparently does not take many parasitic hymenoptera, although some flies 

 are taken. Plant lice sometimes form a considerable portion of its food. No 

 part of the tree where it can find insect food is exempt from its visits, and it even 

 takes grasshoppers, spiders, and myriapods from the ground, grass, or low-grow- 

 ing herbage. 



He (1929) says elsewhere: "It attacks none of the products of man's 

 industry, so far as our records go, except the raspberry, of which it 

 has been known to eat a few occasionally." 



S. A. Forbes (1883) reports that 5 stomachs from a canker-infested 

 orchard contained 94 percent insects ; of which 66 percent were canker- 

 worms, Coleoptera 23 percent, spiders 6 percent, Hymenoptera 2 per- 

 cent, and Hemiptera 1 percent. A. H. Howell (1907) found a cotton- 

 boll weevil in one stomach from Texas; E. R. Kalmbach (1914) re- 

 ports that of seven Utah stomachs, two contained alfalfa weevils, form- 

 ing 25 percent of the food in one; and Prof. Aughey (1878) found an 

 average of 11 locusts in 7 Nebraska birds. 



Behavior. — The gentle little yellow warbler is not only one of the 

 prettiest but one of the tamest and calmest of our bird neighbors. It 



