YUKON CHICKADEE 343 



which are about 3 inches in diameter at the bottom, are invariably 

 lined with a layer of green moss, often at least an inch thick. Upon 

 this layer of moss is a thick lining of rodent fur, cow hair, and other 

 hairy material. 



"Nests containing incomplete sets practically never are occupied by 

 the birds during the day, a coverlet of fur being drawn over the eggs 

 while the birds are away. Incubating birds sit tightly and try to frighten 

 the intruder by a hiss and flutter of the wings when an inquiring finger 

 is poked into the entrance of the nesting hole." 



Eggs. — The Oregon chickadee lays four to ten eggs. Out of 28 sets 

 reported by Mr. Grif^ee, 18 sets consisted of eight eggs; there were only 

 two of six, four of seven, three of nine, and only one of ten. The eggs 

 are practically indistinguishable from those of the black-capped chickadee. 

 The measurements of 40 eggs average 15.6 by 12.0 millimeters; the eggs 

 showing the four extremes measure 17.0 by 12.0, 16.2 by 12.3, 14.6 

 by 11.7, and 14.8 by 11.5 millimeters. 



The plumage changes, food, behavior, voice, and other habits are 

 apparently similar to those of the closely related eastern race. 



Mr. Rathbun observed some of these chickadees eating tent cater- 

 pillars, near Seattle, of which he writes in his notes : *Tt was toward 

 evening, and seeing three of these birds very active in a lilac bush, we 

 stopped to watch them. Near the top of the bush was a tent caterpillars' 

 web of small size ; as the worms were crawling toward it, some of them 

 would be seized by the chickadees for food. During a space of less than 

 five minutes the three chickadees captured and ate eight of the worms 

 of large size. When one was caught the bird would beat it about a 

 number of times and then, holding it with one foot on its perch, leisurely 

 tear off pieces with its bill, which it then ate. The birds must have been 

 feeding on the caterpillars for some time before we noticed them, for, 

 on looking over the ground under the bush, many dead and mutilated 

 worms were to be seen strew about." 



PAUUS ATRIOABPUIiLUS TUR,NERI Rldgway 

 YUKON CHICKADEE 



HABITS 



According to the 1931 Check-list, this chickadee "breeds in the Hud- 

 sonian Zone of northern Alaska north and west of Cook Inlet." 



Ridgway (1904) describes it as "similar to P. a. septentrionalis but 

 sHghtly smaller, coloration grayer above and more extensively or purely 

 white beneath, and white edgings of greater wing-coverts, secondaries, 

 and outermost rectrices broader, more purely white ; in spring and 

 summer plumage the gray of upper parts without perceptible tinge of 



