THE NEST 71 
The Nest 
Enemies of Nesting Birds.—It will add to our appreciation of a 
bird’s resources and most assuredly to our sympathy with birds, if 
before discussing their nesting habits we merely mention some of the 
enemies and dangers which threaten birds at this season. These are 
of two kinds; first, the elements; second, predatory animals including 
parasites. High winds, heavy rains, prolonged wet or cool periods and 
hail-storms are among the weather phenomena often fatal to the life 
of the nest; while chief among the animals that prey upon the eggs or 
_young of our birds, are Crows, Jays, Grackles, cats, squirrels, opossums, 
minks, weasels, skunks, snakes, and man, who either directly, as an 
egg collector for the table or cabinet, or indirectly, in mowing fields, 
clearing hedgerows and in other ways, has won a prominent place among 
the enemies of nest-life. 
With such an array of adverse conditions and relentless foes, the 
bird which reaches maturity may be said to have escaped nine-tenths 
of the dangers to which bird-flesh is heir. One realizes, therefore, how 
important it is for birds to select a site, build a nest, and care for their 
young in a way which has proved to be most desirable for their species; 
and how readily imperfect inheritance of the proper activities or in- 
ability to conform to new conditions may mean failure to rear a brood, 
and in the end extinction of the species. 
Nesting Site—The nature of a bird’s nesting site appears to be 
determined by (1) the necessity for protection; (2) condition of the 
young at birth; (3) temperament, whether social or solitary; (4) 
habit, whether arboreal, terrestrial or aquatic; (5) haunt, whether in 
woodland, field, marsh, etc. ‘ 
Protection may be secured by hiding the nest, by placing it in more 
or less inaccessible situations in trees or on cliffs, or by frequenting some 
isolated islet uninhabited by predatory animals. As I have elsewhere 
said (“Camps and Cruises of an Ornithologist,”’ pp. 35-37), “So far as my 
experience goes, all colonial ground-nesting birds breed only on islands.” 
Auks, Murres, Skimmers, Petrels, Tropic Birds, Gannets, Cormo- 
rants, Pelicans and Flamingoes are examples among North American 
birds, with which Bank Swallows appear to be the only exception. It 
is less to their terrestrial habit than to their gregariousness that we must 
attribute the necessity of an island home for these birds. When nesting, 
all the individuals of a given species, which at other seasons are scat- 
tered over a wide area, are focused in a small space. To find one nest 
is to find all, and to a large degree the fortune of one nest is also the 
fate of its neighbor. 
Even when arboreal, colonial birds like Herons, Spoonbills, Anhingas, 
and Cormorants usually breed in trees growing in water and which are 
thus insulated. The birds just mentioned are all exceptions to the rule 
that terrestrial feeding birds usually nest on the ground, while arboreal 
feeders nest in trees. But here the condition of the young at birth exerts 
