296 



BIOLOGY FOR BllGlXXLRS 





enemies, they multiply unchecked and are becoming an unmitigated 

 nuisance. 



Nest Building. The fact that the bird's egg requires continuous 

 external heat for hatching is a point in which they differ from all 

 lower forms and necessitates the construction of some sort of nest 

 to protect the eggs and retain heat. Next to migration, the highest 

 development of bird instinct is shown in some of their nest con- 

 struction. We must remember 

 that they have no hands or fore- 

 limbs to help, but merely beak 

 and feet, and their materials are 

 only such as they can find. Y<i. 

 when the wonderful home of an 

 oriole or humming bird is studied, 

 we realize that even with hands, 

 and brain, and tools, we could not 

 imitate them. Nests differ widely 

 both as to materials and construc- 

 tion. Earth, clay, sticks, grass, 

 hair, feathers, moss, and even 

 strings are some of the substances 

 used, while the structure itself 

 may vary from a mere hole in the 

 sand (ostrich) to the dainty nest of 

 a vireo. 



Excavated Nests. Water birds 

 often lay their eggs on rocks, with 

 only sticks enough to keep the 

 eggs from rolling; holes in the ground serve for kingfisher, and 

 bank swallows, while owls and woodpeckers excavate homes in 

 hollow trees. 



Woven Nests. Very simple grass nests are made by ducks 

 and wading birds. Among the most remarkable woven nests are 

 the covered pendant homes of orioles and vireos, hanging from 

 slender limbs where no thieving cat or red squirrel can come. 

 Horsehair and plant fibers are used and always seem to be so well 



FIG. 100. Nest of humming bird, 

 made of sycamore down. (One-half 

 natural size.) From Kellogg. 



