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 oological 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 

 {Haliceetus Leucocephalus) lays white eggs ; the Golden Eagle 

 {Aqiiila chrysaetos), 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 {Helifiaia sivainsoni), the 

 Short-billed Marsh Wren {Cistothorus sfellaris), the Arizona 

 Jay {Aphelocoma sieberi ariz07id), Junco pht20?iohis palliatus, 

 and many others, are peculiar in their groups for laying 

 white eggs. This is doubtless a recent change. In one 

 genus of flycatchers {Empidonax) 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 



