68 BIRDS' EGGS. 



which we can give no satisfactory reason. Thus the 

 Crested Flycatcher's strange custom of using a cast 

 snake-skin in its nesting materials prohaljly originated 

 with the l)irds in the tropics, where it is still followed 

 by nearly related species of Crested Flycatchers. With 

 them there may he a reason for this hal>it, but with our 

 bird, living as it does under entirely different conditiijns, 

 it is doubtless only an inheritance, surviving even when 

 the necessity for it has ceased to exist. 



Eighth, change of habit. Some birds are influenced 

 \,j changes in their surroundings, and alter their nesting 

 habits when it proves to their advantage to do so. 

 Chimney Swifts, who have exchanged hollow trees, in 

 which they were exposed to their natural enemies, for 

 the comparative safety of chinnieys, are good examples. 

 But a far better one is given by that prodigy in feathers, 

 the House Sparrow. Is there any available site in which 

 this thoroughly up-to-date bird will not place its nest ? 

 It has taken possession of even the hollow spaces about 

 certain kinds of electric lamps, and has been oliserved 

 repairing its nest at night by their light ! 



The Eg<j'<- — Usually, little time is lost between the 

 completion of the nest and the laying of the eggs. The 

 number of eggs composing what oologists term a full 

 set or clutch ranges from one to as many as twenty. At 

 the time of laying, the ovary contains a large number of 

 partly formed eggs, of which, normally, only the required 

 number will become fully developed. But if the nest lie 

 robbed, the stolen egg will frequently be replaced. The 

 long-continued lajnng of our domestic fowls is an instance 

 of this unnatural stimulation of the ovary. Doul)tless the 

 most remarkable recorded case of egg-laying by a wild 

 Ijird is that of a Fligh-hole or Flicker, who, on being reijii- 

 larly roblied, laid seventy-one eggs in seventy -three days ! 



The eggshell is composed largely of carbonate of lime. 



