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, lavs 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. I 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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