442 The Bird 
contend. Toucans are able to get along with a pair of 
eggs; while a hornbill, by sealing its mate up in its little 
arboreal cavern during nidification, is so adequately 
protected that one to three eggs in each family suffice 
to keep the race going, since practically every young 
Fig. 351.—Burrowing Owl at nesting hole. 
bird is brought to maturity. Of the host of smaller and 
weaker birds nesting in cavities, two to five eggs are the 
usual quota. This brings us to the tribes of little singing 
birds with which we started, whose average is about 
five; but a few interesting exceptions may be noted. 
Our whippoorwills and night-hawks, for instance, lay 
only two eggs. These are placed on the ground in the 
