BIRDS OF NORTH AND MIDDLE AMERICA 635 



of the shaft streaks, in others no well-defined malar stripe is present; 

 chin, throat, breast, abdomen, sides, flanks, thighs, and under tail 

 coverts white, generally with a wash of cartridge buff or cream color, 

 the chin and upper thi'oat usually immaculate, sometimes with dusky 

 shafts; lower throat, breast, and abdomen with dark sepia shafts 

 widening apically into tear-shaped spots; sides, flanks, and thighs 

 usually with the shaft streaks more pronounced and broadening more 

 extensively, even forming transverse bars in some instances; under 

 tail coverts immaculate or marked iilve abdomen; under wing coverts 

 white, barred broadly with dark sepia to fuscous; unfeathered parts 

 as in white phase. 



Juvenal (sexes alike) — White phase. ^^ 



a. Bar-tailed variety: Variable, but similar to the adult (also 

 variable), but with the chaetura-black to dark sepia subterminal 

 crescentic marks on the feathers of the upper surface of the body and 

 wings of the adult enlarged to deep wedge-shaped areas covering most 

 of the exposed portions of the feathers, especially of the scapulars, 

 interscapulars, and upper back, producing almost a scalloped effect 

 on these feathers with the white edges; the shaft streaks on the crown 

 and cheeks generally heavier than in the adult and the tear-shaped 

 streaks on the underparts also heavier and more numerous; the under 

 wing coverts more streaked with dark sepia to chaetura black than in 

 adults; cere and bill pale plumbeous, tarsi and toes pale bluish, claws 

 black; orbital skin pale plumbeous. 



h. Plain-tailed variety: Similar to adults, but Avith the brown 

 markings on the scapulars, interscapulars, and upper wing coverts 

 broader; underparts not more heavily streaked, however; cere and bill 

 pale bluish plumbeous; tarsi and toes pale bluish. 



Juvenal (sexes alike). — Gray phase, pale variety: Variable; entire 

 top of head dark sepia to chaetura drab, the feathers edged with white 

 to pale avellaneous, sometimes the edgings so broad as to reduce 

 the dark color to a mere shaft stripe, in other cases, narrow and rela- 

 tively indistinct, the pale areas usually wider and more noticeable on 

 the nape than on the crown; entire upperparts of body and the upper 

 wing coverts sepia to dark sepia edged narrowly with drab or dirty 

 whitish; in some birds these feathers are unmarked, in others they are 

 transversely spotted (or incom^pletely banded) with buffy white to 

 pale avellaneous, thus producing two quite different types of colora- 

 tion, a uniform and a spotted one; primaries externally and terminally 

 dark sepia, the outer webs may be indistinctly mottled with buffy 



33 It has been suggested by Swann and other writers that the gyrfalcons pass 

 through numerous plumages between the juvenal and adult stages, but I have 

 seen not the slightest evidence of this in a very long series of skins or from liter- 

 ature or accounts of birds raised in captivit^^ To attempt to allocate plumage 

 phases to age chronology seems arbitrary and pointless. 



