364 HOMING WITH THE BIRDS 



would bake them to such a bark-bound state that 

 in two seasons the strongest of them would be dead. 

 I have seen many single trees killed in this manner 

 in northern Indiana and southern Michigan; and in 

 several places I have seen whole orchards wiped 

 out in two seasons. The warblers 'prove them- 

 selves our salvation above all other birds, merely 

 by living their lives according to their evolution. 

 It seems an alarming situation when we realize 

 that we are so dependent upon such frail, tiny crea- 

 tures with the odds so against them. 



Many warblers choose extremely high nesting 

 sites so that they will not have long trips to make 

 in feeding their young. Others nest lower, while 

 some select bushes only a few feet from the ground. 

 These variable nesting locations make these birds 

 prey to all outdoors from the crows and jays of the 

 high treetops to the red squirrels of the middle 

 locations and the snakes, weasels, and skunks of the 

 ground. They suffer peculiarly from the imposi- 

 tions of the cowbirds, as warbler nests are so tiny 

 that two cowbird eggs to a nest practically assure 

 death by starvation and trampling to the warbler's 

 entire brood. One young cowbird can crowd out, 

 trample, and starve half of a warbler's brood. 

 The birds are so small and delicate that they make 

 their migration north later than most birds and in 

 lower flight. As a result, they are particularly 

 susceptible to cold during periods of changeable 

 weather, while their low flight often results in their 



