Birds' Nests and Eggs 



six or eight feet deep, excavated in a bank by the birds themselves 

 after as much as two weeks' work. One possible reason for the 

 choice of such a place is the fact that the young, which are fed on 

 fish, regurgitate large pellets of scales and bones and such indi- 

 gestible matter ; were these dropped beneath a nest built in a tree 

 or on the open ground it would betray the presence of the home 

 to the natural enemies of the bird. Why the cowbird declines the 

 responsibilities of maternity has never been satisfactorily explained. 

 It is certain, however, that there is some good and sufficient 

 reason. 



The European cuckoo, like the cowbird, lays her eggs in 

 the nests of other birds, those of the smaller birds being usually 

 chosen. A certain French writer gives as a reason the fact that 

 the cuckoo cannot lay eggs on succeeding days. How long the 

 interval is has not been decided, but if it is of many days' duration 

 that would be an ample reason for the bird's not building a nest 

 for itself, since the eggs might be stolen were they left unpro- 

 tected until the full complement were laid. The eggs of the yel- 

 low-billed cuckoo are said to be deposited at irregular intervals of 

 from two to five days, and are occasionally found in the nests of 

 other birds. Whether in days gone by they placed their eggs en- 

 tirely in the care of other birds or whether they will do so in the 

 future is of course a problem, but it is quite possible that some 

 such change is taking place. There are birds who, having laid 

 their eggs, cover them up and allow them to hatch by themselves, 

 trusting to the heat generated by the covering chosen. 1 know 

 of none of our eastern birds that do this, yet some of them make 

 use of vegetable substance that has heating qualities. 



The grebes, for instance, use decayed and damp vegetable 

 matter, while many of our small birds place in their nests woolly 

 stuffs and other non-conducting material, probably to protect the 

 highly sensitive eggs from sudden changes of temperature. 



The shapes of eggs show in many instances the forethought 

 of nature. Eggs that are laid on bare rocks and exposed places 

 where little or no nests are made, are generally rounded at the 

 larger end and come almost to a point at the other extremity ; this 

 makes it possible for them to be turned by the wind without roll- 

 ing away ; whereas the ovate or elliptical eggs that are found in 

 well-protected places, such as holes in trees, would soon be blown 

 off by a strong wind in such exposed situations. 



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