GRASSHOPPER SPARROW 733 



Young birds on my Penns3dvania study area remained in the nest 

 9 days. Michigan birds observed by Walkinshaw (1940) remained 

 in the nest the same length of time. When out of the nest, the 

 young run mouseHke through the grass and rarely appear above the 

 grasstops. 



Both male and female are very solicitious about the young. During 

 incubation the birds exhibit little concern about human and animal 

 intrusions in their territories except those of cats. After the young 

 hatch, the birds react to human intrusion with vigorous alarm. They 

 may fly in \vide circles above the trespasser, raising their crest 

 feathers and flicking their wings and tail. On the ground they bob 

 up and down on their legs like a spotted sandpiper (Actitis macularia) 

 and utter a sharp chi-ip. When highly alarmed they give this double 

 note so rapidly it almost runs into a trill. Often the male will inter- 

 rupt his chipping to break into a grasshopper song. If the birds are 

 carrying food to the young at the time, they invariably eat the 

 insect and continue their alarm behavior. When a dog enters the 

 territory, the birds drop into the grass, crouch low, and remain silent 

 until the animal passes. 



Plumages. — The juvenal plumage and post-juvenal molt of the 

 grasshopper sparrow have been studied in detail by George M. Sutton 

 (1935, 1936). He found a number of discrepancies in the descriptions 

 by D\vight (1900), which were apparently based on a poorly aged 

 specimen. 



According to Sutton, the natal down is replaced by the juvenal 

 plumage in a complete postnatal molt. It is worn for a short time 

 as a complete plumage and is probably complete at 10 to 12 days of 

 age. At this time the rectrices are stubby; the feathers of the back 

 and scapulars are plain dark oUve-brown or blackish brown, edged 

 with buff, and totally lack any sort of russet spots on the tips. 

 Richard R. Graber (1955) describes the juvenal plumage in detail as 

 follows: 



"No sexual dimorphism. Forehead and crown streaked, brown and 

 black, with median and supercihary stripes of light buff or buffy white. 

 Nape mottled, buffy white and black. Back, feathers black, edged 

 with buff or buffy brown. Upper tail coverts black, edged with buff. 

 Rectrices black, narrowly edged ^A'ith buff, except median pair (broadly 

 edged). Remiges slate gray or black, edged with buff or buffy brown. 

 Tertials black, edged with white. Superciliary buffy white, streaked 

 with black. Auriculars buffy brown. Post-auriculars concolor with 

 nape. Underparts white or buffy white more strongly tinged \vith 

 buff on chest, sides, flanks, and crissum. Upper chest rather sparsely 

 streaked with blackish or dark brown. Other underparts unmarked. 

 Stub-tailed birds much darker throughout than older birds." 



