92 KINSHIP OF BIRDS, AS SHOWN BY EGGS. 
bluish-green in varying intensities, and these are the normal 
tints among the Heron-forms, whose eggs are unmarked 
usually. In their markings Hawks’ eggs more nearly re- 
semble the Cranes’, which are boldly dashed with blackish or 
reddish brown and purplish dottings. Among the Crane- 
forms is found also a bird with evident Hawk-like shape and 
habits—justifying the odlogical suggestion. This is perhaps 
more evident through the ground-building Vultures, which 
certainly furnish at least one strain that comes into the Hawks 
and Eagles. 
In these higher accipitrine forms the color of the mark- 
ings is much lighter, as if diluted, and a very strong tendency 
is shown toward omitting it altogether. Many perfectly un- 
marked eggs and even whole clutches are found among 
birds that usually lay marked eggs. The Bald Eagle 
(Halizétus Leucocephalus) lays white eggs ; the Golden Eagle 
(Aguila chrysaétos), usually one egg marked and one un- 
marked ; and the most extravagant variations prevail gener- 
ally throughout the group, superinduced, doubtless, by com- 
paratively recent changes in nesting. 
The Caracaras (Polyborus) lay extravagantly marked eggs, 
frequently having the whole stained deeply, indicating their 
vulturine kinship; but their great variations show a tend- 
ency to struggle upward to the higher birds of prey which 
the birds’ other habits scarcely endorse. 
Of course the eggs of different species may distinguish 
them readily. Swainson’s Warbler (Helinaia swainsoni), the 
Short-billed Marsh Wren (Cistothorus stellaris), the Arizona 
Jay (Aphelocoma sieberi arizona), Junco phaonotus palliatus, 
and many others, are peculiar in their groups for laying 
white eggs. This is doubtless a recent change. In one 
genus of flycatchers (Zmpidonax) the species have to be 
diagnosed by nest and egg; and in other instances, as is 
well-known in the case of Gulls and Plovers, the relationship 
was first suggested by similarity of egg-markings. The 
marked differences between the eggs of the black and brown 
