THE YOUNG BIRD 
79 
concerned. Fully adult, vigorous birds probably lay larger and more 
heavily pigmented eggs and more of them than their younger or weaker 
fellows. Again, the first eggs of a set, as well as those of first sets, where 
more than one is laid, may be more strongly pigmented or larger than 
those laid later. But whatever their cause, the cataloguing of these 
variations constitutes no small part of the labors of the oologist, whose 
delight in finding an unusually large set, or one containing ‘runt’ eggs, 
or colored eggs which should be plain, or plain eggs which should be 
colored, is somewhat out of proportion to the scientific value of the 
‘discovery.’ 
Incubation . — The period of incubation is more or less closely related 
to the size of the egg. With the Chipping Sparrow it is twelve days, 
but with the Ruby-throated Hummingbird fourteen; the English 
Sparrow requires twelve or thirteen, the Robin thirteen or fourteen, 
the Fish Hawk about twenty-eight, but the exact period has been 
ascertained for comparatively few of our birds. 
Incubation is usually performed by the female and is sometimes 
equally shared by the male; or the male may merely cover the eggs 
during the female’s absence; or again, as with the Ruby-throated 
Hummingbird, he may not be seen near the nest after the eggs are 
laid. With the Phalaropes the male alone incubates. 
The treatment of their eggs by sitting birds is a subject concern- 
ing which we have not much information, though some birds are known 
to turn them with their feet and others with their bills. I have seen a 
Least Bittern calmly eat two of her five eggs which had been punc- 
tured by a Marsh Wren, and then settle herself on the remaining three. 
(“Bird Studies with a Camera,” p. 75.) 
The disposal of the egg-shell is also a matter of interest. Most 
birds carry it some distance from the nest before dropping it, but young 
Flamingoes eat it! 
The Young Bird 
Condition at Birth . — The treatment of the young bird during its 
period of dependence on parental care is determined primarily by its 
state on leaving the egg. If it be prsecocial and hence runs or swims 
with the parent the day it is born, its early life will differ greatly 
from that of the altricial bird, which hatched naked, blind and help- 
less, is reared in the nest. 
In either case, the act which in natural succession follows incubating 
is brooding. Prsecocial birds are usually hatched within a few hours 
of each other, and are as a rule brooded in the nest only until the water- 
proof sheath, in which their natal down is enclosed, is dry and slits, 
transforming the nestling from an apparently scantily haired little 
creature to one thickly covered with down. After that they are brooded 
only at night or when, tired, they are permitted to ‘snuggle’ beneath 
the parental breast. 
