OF EASTERN PENNSYLVANIA. 195 



pendecl in the labor of building seldom exceeds a single 

 night, although instances have occurred where the greater 

 part of a second night was thus occupied. The task is 

 somewhat intermittent in its character, the birds alternately 

 working and feeding. 



Mr. Dall, in his notes on the birds of the Aleutian Islands, 

 asserts that on Unalashka, a horizontal hole is excavated 

 for a nesting-place 'to the depth of two feet ; the further 

 extremity being somewhat higher than the other, and lined 

 with dry grasses and feathers. Owing to the absence of 

 trees, the birds were discovered sitting upon the ground 

 close by the mouth of their burrows, during the daytime. 



The nest being finished, the female begins to deposit her 

 complement of eggs almost immediately. The maximum 

 number is seven. We have frequently met with nests 

 that, contained from four to five, but never a less number. 

 The eggs are laid on consecutive days, and invariably at 

 the rate of one egg per day. Incubation instantly follows 

 and continues for a period of eighteen days. It is the joint 

 labor of the sexes, who relieve each other at somewhat 

 regular intervals, both during the day and night. Occa- 

 sionally we have discerned both birds upon the nest at the 

 same time during the day, where the nest was sufficiently 

 capacious ; but, ordinarily, the non-incubating bird is close 

 at hand when called to the relief of his partner. While 

 with eggs and young, these birds are exceedingly jealous, 

 and will not permit a feathered stranger to encroach within 

 their territory, without inflicting a severe punishment upon 

 his temerity. Human intruders are received with demon- 

 strations of great anger and excitement, the parents uttering 

 alternate sibilant and clicking sounds, and even venturing 

 to assail them with protruded talons. 



The young are tenderly cared for and diligently protect- 

 ed, one or the other parent remaining in the vicinity of the 

 nest to guard against danger. Being ravenous feeders, they 

 severely tax the physical energies of their parents to the 



