OLIVE-BACKED THRUSH 181 



on throat, breast and sides, and heavily spotted with black on the 

 breast and sides of throat, the fore parts and sides of whiter abdomen 

 indistinctly barred. Sides of head buff, spotted with black; orbital 

 ring distinct, pale ochraceous buff; submalar stripes black." 



The first winter plumage is acquired by a partial postjuvenal molt, 

 beginning about the middle of August and involving all the body 

 plumage and the lesser wing coverts, but not the rest of the wings 

 nor the tail. This is essentially like the adult winter plumage, but the 

 upperparts are somewhat less richly colored and the spotted median 

 wing coverts are retained until the following summer. 



At next postnuptial molt, which is complete in August and Sep- 

 tember, adults and young become indistinguishable. Both young and 

 old birds in fall and early winter are richly colored, above deep olive- 

 buff in young birds and rich brownish olive in adults; and the sides 

 of the head, throat, and upper breast are washed with rich ochraceous- 

 buff. There is apparently no spring molt, but wear and fading have 

 produced a somewhat grayer back, and the buffy tints are much paler 

 in spring birds. 



Food. — Professor Beal (1915b) examined the contents of the stomachs 

 of 403 olive-backed thrushes, from widely scattered localities in the 

 United States and Canada, and distributed over nine months from 

 March to November. The food consisted of 63.52 percent animal 

 and 36.48 percent vegetable matter. He writes: 



Beetles of all kinds amount to 16.29 percent. Of these 3.14 percent are of the 

 useful Carabidae. The others belong to harmful or neutral families. Weevils 

 or snout beetles (Rhynchophora) amount to 5.29 percent, a high percentage for 

 such insects. One Colorado potato beetle (Leptinotarsa decendimeata) was found 

 in a stomach taken on Long Island. Hymenoptera collectively aggregate 21.50 

 percent. Of these, 15.20 percent are ants — a favorite food of Hylocichla. The 

 remainder (6.30 percent) were wild bees and wasps. No honeybees were found. 

 Caterpillars, which rank next in importance in the food of the olive-back, form a 

 good percentage of the food of every month represented and aggregate 10.30 

 percent for the season. 



Grasshoppeis are not an important element in the food of thrushes, as they 

 chiefly inhabit open areas, while Hylocichla prefers thick damp cover, where 

 grasshoppers are not found. An inspection of the record shows that most of 

 the orthopterous food taken by the olive-back consists of crickets, whose habits 

 are widely different from those of grasshoppers, and which are found under 

 stones, old logs, or dead herbage. The greatest quantity is taken in August and 

 September. The average for the season is 2.42 percent. 



Diptera (flies) reach the rather surpiisingly large figure of 6.23 percent. These 

 insects are usually not eaten to any great extent except by flycatchers and 

 swallows, which take their food upon the wing. The flies eaten by the olive-back 

 are mostly crane flies (Tipulidac) or Maich flies (Bibio), both in the adult and 

 larval state. Crane flies are slow of wing and frequent shady places. The 

 larvae of both groups are developed in moist ground, and often in colonies of 

 several hundred. With these habits it is not surprising that thev fall an easy 

 prey to the thrushes. 



