CLASS AVES 



419 



435. Reproduction. — Birds may mate either for the rearing of a 

 single brood or for life. The nesting locaUty seems to be in most cases 

 chosen by the male, though it is the female which determines the precise 

 location of the nest. One or both members of a pair take part in its 

 construction, which varies greatly among different types of birds. Some 

 birds make no nest but lay their eggs directly upon the ground (Fig. 309). 

 Others make crude nests by scratching out hollows and then utilizing 

 a few pebbles, twigs, or bits of grass. At the other extreme in nest 

 building are the beautifully woven pendant nests of orioles, especially 

 of certain tropical ones, which in many cases are several feet in length. 

 Some birds do not rear their own young but deposit their eggs in the 



Fig. 309. — "Nest" of a Texas nighthawk, Chordeiles acutipennis texensi Lawrence. 

 Blotched eggs laid on coarse gravel with no prepared nest. The markings on the eggs render 

 them inconspicuous on the gravel. (Photographed, copyrighted, and contributed by Gayle 



PickweU.) 



nests of others who become foster parents. This is true of the European 

 cuckoo and of some American cowbirds. In these species mating of 

 one bird with a single one of the opposite sex does not take place, for 

 each female mates with many males, a phenomenon known as polyandry. 

 On the other hand, as in the case of ostriches and of some fowls, one male 

 may mate with several females, and this is known as polygyny. 



Birds' eggs vary greatly in size, color, and number. The size of the 

 egg bears a general relationship to the size of the bird, while the number 

 is greatest in those birds whose nests are most exposed to destruction. 

 The color of eggs is related somewhat to the place where they are laid. 

 Those laid in cavities are usually white, or white with reddish spots; 

 those upon the ground are usually streaked or mottled in such a way as to 

 resemble the surroundings (Fig 309) ; and those in nests in trees and bushes 

 are frequently blue or bluish white with markings of various patterns. 



