120 HIGHWAYS AND BYWAYS. 
bird hatches its first brood in one of the most artistic 
little domiciles, substantial and well lined to keep out 
the cold and wet, but the second and third broods, 
hatched later in the season when the weather is warm, 
are put off with a slimsy makeshift of a nest, often so 
thin and sleezy that one can see the eggs and young 
through the bottom of it as readily as through a sieve. 
The orioles that nest in Pennsylvania do not use half 
the material that those do which nest in Canada and 
Northern New York. Old birds in many cases not only 
make much better nests than the younger ones, but are 
also much better singers, some of them even adding new 
bars and strains to their songs. The cow-bunting makes 
no nest of her own, but deposits an egg in the nest of 
another bird: this she does surreptitiously and generally 
as soon as the nest is finished. We all know the inge- 
nuity exercised by some of the little birds thus imposed 
on, to prevent the incubation of this foreign egg. 
The blue-eyed warbler (Dendroica estiva), and one or 
two of the vireos build another department, and wall in 
the egg of the interloper. So general has become the 
custom of the bunting to use the nest of the blue-eyed 
warbler, that the little bird now often makes provision 
for the emergency when sbe constructs the nest, by 
building it deep enough for the two compartments. 
Bird migration has always been an interesting prob- 
lem to naturalists who do not attribute all phenomenal 
intelligence to natural instinct. It may be called hered- 
itary instinct, learned through accident, perhaps, or 
acquired by necessity and afterwards transmitted from 
