CHESTNUT-BACKED CHICKADEE 387 



As to the nest itself, Mr. Bowles (1909) writes: "The cavity is 

 usually about seven inches in depth, seldom any more, tho occasionally 

 much less. Almost any soft substance to be found in the vicinity is 

 used to make up the nesting material, but there is always a substantial 

 foundation of green moss. Cotton waste from factories, liair of cows, 

 squirrels, rabbits and goats, and small feathers are most often used, 

 one very beautiful nest in my collection being composed almost entirely 

 of feathers from the Kennicott Screech. Owl (Ottts asio kennicottii). 

 No matter how large the bottom of the cavity may be, it is always 

 packed tight, and I have sometimes removed a nest that v/ould easily fill 

 both hands." 



Mr. Burleigh's (1930) nests contained similar materials, including 

 horsehair, feathers of a Steller's jay, rope fiber, and v/hite fur of a 

 cat. 



Eggs. — The chestnut-backed chickadee most commonly lays a set of 

 six or seven eggs, sometimes only live, frequently eight, and some- 

 times as many as nine. Mr. Bowles (1909) says that "the eggs vary 

 greatly in both shape and size, some being shaped like a quail's egg, 

 others like a murre's egg." But moct of the eggs that I have seen are 

 ovate or short-ovate, though some are slightly pointed. 



The ground color is pure white, and they are sparingly sprinkled vv^itl? 

 reddish brown or light red dots, sometimes with "sayal brown" or 

 "snufT brown"; the markings are sometimes concentrated about the 

 larger end of the egg, but oftener they are irregularly distributed; some 

 eggs are evenly sprinkled with fine dots, and some are nearly or quite 

 immaculate. The measurements of 40 eggs average 15.3 by 12.0 milli- 

 meters; the eggs showing the four extremes measure 16.2 by 12.2, 14.9 

 by 12.6, 14.4 by 12.0, and 15.9 by 11.3 millimeters. 



Young. — The exact period of incubation does not seem to liave been 

 determined for this species. Dawson (1923) and Bowles (1909) bctli 

 state that incubation begins when the first egg is laid, as the sizes of 

 the embryos in a set of eggs vary considerably. Perhaps the bird does 

 not incubate all through the laying period, but she covers the eggs when 

 she leaves the nest, which keeps them warm, and furthermore, the nest 

 is usually fully exposed to the heat of the sun, which helps the prog- 

 ress of embryo development. 



The chickadees are very brave in the defense of their nest and resort 

 to the common chickadee habit of hissing and fluttering their wings in a 

 startling manner when an intruder looks into the nest. 



Undoubtedly both parents assist in the care and feeding of the 

 young, though we have no definite data on the subject. They seem to 



