BICKNELL'S THRUSH 207 



ment then proceeds rapidly, and by the tenth day the young appear 

 to be nearly fully feathered in the buffy-brown, much bespeckled 

 plumage characteristic of young thrushes. 



This juvenal plumage is replaced by the first winter plumage during 

 the postjuvenal molt in August. All the contour feathers except the 

 remiges and rectrices are shed. Birds still in juvenal plumage were 

 occasionally seen early in August, but before the end of the month, 

 and particularly early in September, both young and adults began 

 to emerge from their late-summer seclusion in full fall and winter 

 dress. The adults undergo a complete postnuptial molt (shedding 

 the remiges and rectrices) in August; the molt of the young is partial. 



The postjuvenal molt was observed fairly closely in a confined sec- 

 ond-brood bird, but the time of molt was not normal, since the bird 

 was taken from a much belated nest. The initial stages may have 

 escaped detection in spite of close watch, since in preening he fre- 

 quently pulled out a feather and ate it; but by August 31 feathers 

 were dropping uneaten to the floor of his cage. Raggedness was first 

 noticed about the various head regions. The posterior nasal area 

 was soon practically featherless, dotted by the incoming quills of the 

 new plumage. Feathers next disappeared from the gular region, and 

 then over the entire head and cheeks, new feathers quickly replacing 

 those lost. The back and breast feathers had an unkempt appearance 

 and gradually dropped out, their disappearance and replacement by 

 the brownish-olive (unspotted) feathers of the first winter plumage 

 indicating the progress of the molt. In another week feather re- 

 placement was practically complete, with one buffy juvenal feather 

 clinging to the head and another persisting on the shoulder. 



Normally there is not supposed to be a spring or prenuptial molt, 

 and the slightly grayer breeding plumage is derived from the more 

 olive-colored winter plumage by wear. The confined bird referred to 

 above, however, grew a new tail in midwinter and in spring molted 

 some wing and body feathers. This was interpreted as an abnormal 

 molt due to poor feather condition, but the abrupt change in plumage 

 from winter to spring in some Alaskan graycheeks suggests that 

 spring molts in nature are not unknown. 



Food. — During the breeding season Bickn ell's thrush is strongly 

 addicted to an insectivorous diet, for the amount of animal matter 

 in the stomachs examined was practically 100 percent. W. L. Mc- 

 Atee has furnished the following data from the records of the U. S. 

 Fish and Wildlife Service: Prof. F. E. L. Beal examined the contents 

 of five stomachs, three from Mount Mansfield, Vt., and two from 

 Slide Mountain, N. Y., all taken on the breeding grounds from June 

 22 to July 2. The total contents of the five stomachs included the 

 following percentages of the various items: Formicidae, 39.6 percent; 



