BICKNELL'S THRUSH 205 



naked except for wisps of wet natal down on the cephalic and dorsal 

 feather tracts. Weighing less than 2 grams at birth, the birds showed 

 a gain of 1 to 2 grams daily up to about 22 grams on their tenth day, 

 after which taking weights and measurements proved impractical, 

 causing the young to leave the nest prematurely. Weights tapered 

 off considerably after the eighth day, presumably owing to rapid 

 feather development. At nest-leaving age the tarsus, bill, and toes 

 are practically full grown, but the wing is only half the adult size and 

 the tail about one-fifth grown. More complete details on daily 

 growth and development have been given by Wallace (1939). 



Considerable variation occurs in feeding schedules at different 

 nests and at different times, but for the most part a more or less 

 standard schedule of 10-15 minute feedings is maintained, usually 

 with a notable concentration early in the morning and a definite 

 slackening early in the afternoon. The female usually proves more 

 efficient and punctual in feeding operations. The male is apt to be 

 irregular, but he effectively concentrates his efforts on critical periods, 

 such as during heavy or prolonged rains, or in the early morning, at 

 which time the female usually remains at the nest to brood. At one 

 nest watched during a 2-hour period of slow rain the male alone 

 maintained the standard schedule of 10-15 minute feedings, while 

 the female stayed on the nest. During periods of mild weather, 

 however, the male may disappear for hours at a time. Food brought 

 by the male while the female is brooding may be parceled out by him 

 to the young, or it may be taken by the female to distribute among the 

 nestlings. At one nest three adults were found feeding the young. 

 At another nest the male deserted, leaving all family responsibilities 

 to the female. She succeeded alone, probably owing to the fair weather 

 prevailing at that particular period, but it might have been a different 

 story if inclement weather had intervened. 



The food brought to the young was not closely or technically 

 analyzed but was known to include many lepidopterous larvae (par- 

 ticularly geometrids), ants, wasps, and other Hymenoptera, and 

 young grasshoppers (especially at one nest near a grassy opening). 

 Large blister beetles (Epicauta cinerea), available on Amelanchier 

 blossoms near one nest, were not utilized, even when gathered by 

 hand and placed on the nest. A severe outbreak of sawfly larvae 

 (Pristiphora geniculate), which threatened complete defoliation to 

 the mountain ash, occurred that summer (1935), and many of the 

 readily available caterpillars were brought to one belated nest of young; 

 but they obviously did not like the strongly flavored larvae and often 

 spit them out, as did a captive nestling force-fed on the 

 spicy caterpillars. 



The stomach contents of four dead nestlings consisted of the 



