among which is the coinpclUng one of a return to the spot ulieif they first saw 

 the hght, or where they reared last season's brood. 



Whatever the cause, the birds arc not discouraged by the many and great 

 perils that attend migration, and vast numbers every year succumb to them. 

 Storms, especially off-shore storms, constitute the gravest peril, and there is 

 abundant evidence that millions of birds are annually blown out to sea to final 

 watery graves. Perhaps no family suffers more in the aggregate than the war- 

 blers. Thinly feathered, delicately organized, highly insectivorous, they are ex- 

 posed to uini>u:il dangers while Ijirds of passage to and from their nesting 

 grounds. 



It is a matter of common observation that every few years in some given 

 locality, perhaps embracing a region of considerable size, a particular species of 

 warbler or other bird suddenly becomes rare where before common. After a 

 season or so, though sometimes not for years, the equilibrium is reestablished 

 and the numbers are as before. These changes very probably are the visible signs 

 of migration catastrophies, the result of the sweeping away of a migration wave, 

 composed of one or of many species, in the path of some sudden storm. 



Again, many of us have witnessed the dire effects of a prolonged rain and 

 sleet storm in spring, when thousands of luckless migrants find only too late that 

 they have permanently left the warmth and plenty of their tropical winter 

 refuges. Under such circumstances thousands of migrants perish from the com- 

 bined eft'ects of cold and starvation, and among them are sure to be great numbers 

 of warblers. 



ECONOMIC VALUE OF WAKBLERS 



From the esthetic point of view, our warblers, as a group, occupy a high and 

 unique position. They also occupy no uncertain place in the list of our useful 

 birds. Preeminently insectivorous, they spend their lives in the active pursuit of 

 insects. They begin with the eggs, preying upon them whenever and wherever 

 found, and continue the good work when the egg becomes the larva and when the 

 larva becomes the perfect insect. 



They are especially valuable in this respect because of the protection they 

 lend to forest trees, the trunk, bark, and foliage of which they search with tireless 

 energy. Their efificiency is vastly increased because the many different species 

 pursue the quest for food in very different ways. While some confine their 

 search chiefly to the trunks and large branches and examine each crack and 

 crevice in the bark for eggs or larvae, others devote their energies to the twigs 

 and foliage, scanning each leaf and stem with eager eyes. Still others descend 

 to the ground and examine the rubbish and grass for hidden prey, while nearly 

 all are adept at catching insects on the wing. 



Each species, however, has a method of its own, more or less unlike that of 

 its fellows, and each excels in some specialty. Not only does the group as a whole 

 specialize on insects, but each individual member of the group still further spe- 

 cializes, so as to leave no loophole for the escape of the enemy. 



The quantity of animal food required to drive an avian engine at full speed 



831 



