NESTS AND NEST-BUILDING IN BIRDS 



177 



many variables to be reckoned with, and each species must be 

 considered separately in reference to them all. If the most 

 important variables are color in adult, egg, and young (r, c i, 

 C2), the correlative instincts and powers of adult and young 

 {c. i.), and the nesting habits {n. h.), their relative scale of im- 

 portance in a given species with reference to protection at a 

 given period, may stand as c, c.i, n.h, while in another species 

 this order may be reversed to ti.h, c.i, c, or with the main stress 

 laid u])on instincts, to the apparent neglect of any of the phases 



Figure 2 — Nest and egg of rose-breasted grosbeak, Hobia ludovicuina, removed 

 from support; fairly deep, symmetrical cup; loosely molded of twigs only, 

 the finest added last; statant type of increment nest. 



of color or even of the structure of the nest. To hazard a pure 

 conjecture, the apparent contradictory nature of color phenom- 

 ena in such animals may be due to the fact that their position 

 in the scale of selected values has shifted, perhaps more than 

 once, and been overlaid in consequence of the greater import- 

 ance of other factors; the more elusive perhaps, but none the 

 less important are the correlated instincts of adult and young. 

 " Perfection " in Nest-Building. The nests of birds are often 

 described as more or less perfect or imperfect, according as 

 they seem to measure up to the standard of the species. Imper- 



