The Wilson Warblers 



the young have hatched out, they take care not to be seen in the vicinity 

 of their nest, but a low, anxious chuck sometimes escapes from the harassed 

 mother in a neighboring thicket. 



No. 100 



Wilson's Warbler 



No. 100a Alaska Pileolated Warbler 



A. O. U. No. 685a. Wilsonia pusilla pileolata (Pallas). 



Description. — Adult male: Above bright olive-green (warbler green); forehead, 

 sides of head, and underparts bright yellow, shading on sides into color of back; crown 

 or "cap" lustrous black; wings and tail fuscous, edged with olive-green and without 

 peculiar marks. Bill dark above, light below; feet light brown. Adult female: Simi- 

 lar, but the black cap sometimes wanting — dark olive veiled by warbler green tips 

 instead. Immature: Like respective sex of parents, but black of cap sometimes 

 variously, or even completely, veiled by olive-green. Both sexes in autumn suffer some 

 veiling of black crown by olive-green tips. Length about 120.6 (4.75); wing 56 (2.20) 

 tail 50 (1.97); bill 8.5 (.33); tarsus 18.8 (.74). 



Recognition Marks. — Least — pygmy size; black cap of male distinctive; 

 recognizable in any plumage by small size and greenish yellow coloration. Brighter 

 than W. p. pusilla; not so bright as W. p. chryseola. 



Nesting. — Does not breed in California. Nest and eggs much as in next form. 



Range of Wilsonia pusilla.- — North America, breeding chiefly north of the United 

 States, save in the Rocky Mountain region and in the Pacific Coast states; winters 

 in Mexico and Central America. 



Range of W. p. pileolata. — Western North America, breeding in Boreal zones 

 from northern Alaska, south upon the Pacific slopes to Queen Charlotte Island, and 

 upon the east side of the Sierra-Cascade system through eastern Oregon and eastern 

 California and along the Rocky Mountains to northern New Mexico and western 

 Texas; wintering from north central Mexico to Panama. 



Distribution in California. — Fairly common migrant through southern Cali- 

 fornia, especially east of the desert divide. Also breeds in the mountain ranges east 

 of the Sierras and for an undetermined distance northward. Possibly the line of 

 demarcation between pileolata and chryseola should be arbitrarily set at the Sierran 

 divide. 



Authority. — Grinnell, Pac. Coast Avifauna, no. 11, 1915, p. 152. 



THE PERVADING yellowness of this little bush-ranger will hardly 

 serve to distinguish it from the equally common Lutescent Warbler, 

 unless you are able to catch sight of its tiny silken crown-patch of black, — 

 the "little cap" which gives the bird its Latin-sounding name. With 



5*3 



