106 BIRDS THROUGH AN OPERA-GLASS. 
poses upon its brothers in the same systematic 
manner. It employs subtle measures, however, 
and the resuit of its work is much worse than that 
of the kingbird. Audubon says, “ Like some un- 
natural parents of our own race, it sends out its 
progeny to be nursed.” Coues says of its habits: 
“Like the European cuckoo, it builds no nest, 
laying its eggs by stealth in the nests of various 
other birds, especially warblers, vireos, and spar- 
rows; and it appears to constitute, furthermore, 
a remarkable exception to the rule of conjugal 
affection and fidelity among birds. A wonderful 
provision for the perpetuation of the species is 
seen in its instinctive selection of smaller birds as 
the foster-parents of its offspring; for the larger 
ege receives the greater share of warmth during 
incubation, and the lustier young cowbird asserts 
its precedence in the nest; while the foster-birds, 
however reluctant to incubate the strange egg 
(their devices to avoid the duty are sometimes 
astonishing), become assiduous in their care of 
the foundling, even to the neglect of their own 
young. The cowbird’s egg is said to hatch sooner 
than that of most birds ; this would obviously con- 
fer additional advantage.” 
The birds upon which the cowbird imposes 
sometimes build a second floor to their houses 
when they find the big stranger egg in their 
home, and a case is given where even a third story 
was built. The cowbird spends a large share of 
