132 THE UNIVERSITY OF THE STATE OF NEW YORK 



e Variation in color and markings in species 



Song sparrow, eggs showing maximum varia- 

 tion Nu SpR3 

 Swamp sparrow, normal eggs Nu SpS2 

 Swamp sparrow, abnormal eggs Nu SpS3 



4 Shape 



The usual shape of eggs is ovoid, but ov^^ls lay eggs that are 

 nearly spherical and sandpipers very pointed ones. 



a Normal — ovoid 



Rose-breasted grosbeak Nu GtR2 



h Pointed 



Upland plover Nu PpU2 



Spotted sandpiper Nu ST24 



In what sort of nests are such pointed eggs found? What is 

 the special advantage of this shape? 



c Spherical 



Great horned owl Nu OwG2 



5 Incubation 



The purpose of incubation is to maintain the eggs at a uniform 

 temperature approximately that of the body of the brooding bird. 



Birds ordinarily lay one c^^ each day and do not begin to 

 incubate until the normal complement is complete so that the 

 eggs will all hatch at approxiihately the same time and the young 

 have an equal chance to grow. The owls, the bitterns and the 

 cuckoos, however, sometimes lay eggs at irregular intervals and 

 begin incubating before the complement is complete. The eggs 

 do not hatch at the same time and the young in a nest may be of 

 various sizes. 



a Begins when 



(1) Usual — with the laying of the last egg so that eggs 



hatch together and young all same size 

 Chickadees Nu Ci4 



(2) Unusual — with the laying of first egg before comple- 



ment is complete 



Black-billed cuckoo, young and eggs in .; 



same nest Nu CvBS 



Bittern, young of very different sizes Nu BiA6 



Screech owl, young, several days differ- 

 ence in age Nu OwS24 



