xx THE STORY OF THE BIRDS. 
incubation. Style of nest likely also a factor of the amount 
needed. 
For Study.—Note the duration of incubation of various do- 
mestic and wild birds near. Observe the relations between size 
of parent, of egg, of nestling, and of time incubated; also rela- 
tion of style of nest to number of young and the time they stay 
in nest. Observe also duration of laying period and time used 
in depositing each egg. Report to some ornithological journal. 
CHapreR XVII.—The style of a nest affected both by in- 
herited tendencies and present surroundings. Centers of origin 
thus hinted. Different building seasons (early or late) affect the 
structure. No fossil nest, no embryology of nesting, but present 
elements hint past development. Platform, cup, and lining likely 
represent three different stages of progress. The “ natural-selec- 
tion” element of structure and location mentioned. The lining 
the most recent and constant feature. Intricate nests made for 
comfort of nestling or sitting parent. Tree building a great 
nest-developing element. Nests often ornamented or at least 
concealed by mimicry of surroundings in form and color ; shaped 
also by color of sitter. 
For Study.—Note that nests of hens, geese, turkeys, ete., are 
mere hollows, showing little structure. Note just above them 
pigeons moving the material, but making poor nest. Separate 
platform, cup, and lining of old robin’s nest. Note chipping 
sparrow’s tendency to emphasize the lining and omit the plat- 
form. Note frequent simple cups (not purses) of Baltimore 
oriole. Make notes of variations in all nests examined. 
CuarprerR XVIII.—A few birds seem quite fastidious about 
nesting material and location. The sham nests of wrens and 
gallinules mentioned and purpose discussed. The trades of 
- birds. Old nests not usually used a second time except in holes, 
ete. Frequent theft of each other’s material and nesting sites. 
Nest repairing by owls, eagles, and ospreys. 
For Study—Watch blackbirds and any old nests that are in 
the yard. Nail up gourds, cans, and boxes anywhere that they 
can be observed, with holes too small for sparrows, and thus at- 
tract house wrens, tits, and chickadees for study. 
CuapteR XIX.—AII colors and markings of birds’ eggs once 
likely had purpose in them. LEarliest birds’ eggs probably pure 
