OF EASTERN PENNSYLVANIA. 45 



during the months of November, December, and 

 January. During the rigor of these months it 

 cannot be doubted but that the species discovers 

 in hollow trees the warmth and shelter which it 

 requires. Many of our winter denizens select 

 similar situations in order to escape the cold. It 

 is worthy pf remark here, that these to a consider- 

 able extent, nidificate in like situations. We might 

 instance Lophophanes bicolor, Parus atricapillus, 

 Certhia Americana, Sitta Carolinensis, and the 

 Picides as dwelling in hollow trees during the 

 inclemency of winter, and utilizing similar situa- 

 tions for nesting-purposes. 



From these data we argue that our eastern 

 species of Blue Bird, learned to build in hollow 

 trees by first using such places for shelter during 

 the ■ inclemency of weather which prevailed on 

 their early arrival ; a;nd perceiving the comfort and 

 convenience of such situations, have come to 

 regard them as appropriate quarters for nesting 

 purposes. Thus what was merely accidental, has 

 become intuitive and habitual. 



Coming back from this digression, after a 

 judicious selection of locality, the birds set to 

 work to collect nesting-materials. Soft grasses, 

 hair, feathers, and wool- when the latter is obtain- 

 able, are gathered and arranged with little regard 

 to design. The time required seldom exceeds 

 five days at the utmost. Shortly after the com- 

 pletion of the nest, oviposition commences; the 

 usual complement of eggs being laid within a 



