19H] Grinnell: Mammals and Birds of tin Colorado Valley 195 



except facially, where it is replaced on the chin, lores, superciliary 

 line, lower eyelid and fore part of auriculars with the clear greenish 

 yellow peculiar to V. c. lutescens. This abrupt replacement is bilater- 

 ally uniform and so conspicuously in evidence as to suggest the style 

 of coloration in the yellow-faced gray-bodied verdin. It is probable 

 that the warbler in question is a hybrid between V. c. celata and V. c. 

 lutescens, having been bred in a region where the ranges of these 

 two forms meet. Such a locality is Prince William Sound, Alaska 

 (see Grinnell. 1910, p. 409). 



Vermivora celata lutescens (Ridgway) 

 Lutescent Warbler 



Common as a migrant, chiefly in April and May. Two specimens 

 taken February 23 and 28 at Mellen, Arizona, may have been winter- 

 ing in the region ; no more were encountered until March 29, at Ehren- 

 berg, when two in full song came to notice; thereafter the species was 

 observed almost daily, though not in numbers. The willow strips 

 formed the main forage-ground. The last specimen was taken May 7, 

 on the California side near Pilot Knob. 



The eleven specimens preserved (nos. 13563-13573) are varyingly 

 grayer than breeding birds (May and June) from the Pacific Coast. 

 But it is clear that a slight ashy obscuration in some degree accounts 

 for the duller yellow of the early spring birds. The underlying yellow 

 of the male appears just as intense in February and March examples 

 as in June birds. Wear removes most or all of the ashy feather tips. 



Dendroica aestiva sonorana Brewster 



Sonora Yellow Warbler 



First encountered April 8, a single adult male, on the Arizona side 

 ten miles below Cibola; next noted April 10, two in song on the 

 California side, twenty miles north of Picacho; many on the morning 

 of the 17th near the same place. When we reached our station on 

 the California side eight miles east of Picacho, April 17, Sonora yellow 

 warblers were abundant. As this was a particularly favorable locality, 

 more so than the last, it is fair to infer that the species had arrived 

 in force some days previously. Even so, the first appearance of yellow 

 warblers along the Colorado River was later than the usual date of 



