76 INHERITANCE 
some exceptional cases of birds, like Pelicans, Water-Turkeys, and 
Cormorants, which, while low in the evolutionary scale, have altricial 
young, and in consequence build well-formed, complex nests. The 
Noddy Tern, sole tree nest-builder of its group, usually constructs in 
bushes a nest of sufficient strength to harbor the young for two 
months. (Thompson, Bird-Lore, V, 1903, p. 81.) 
Other low types of altricial birds secure shelter for their helpless 
young without actually building a nest, but by using a natural cavity 
in tree or cliff, or by making a burrow, and we doubtless have here a 
primitive type of bird home. 
It is impracticable to go into further detail here, but the study of 
birds’ nests may be indefinitely extended by taking up certain species 
of birds and considering their nesting-habits in the light of what appears 
in this chapter. 
Inheritance—There is no reason to doubt that nest-building is 
as much an instinctive activity with birds as it is with bees or wasps. 
Some writers would have us believe that the young bird in the nest 
makes mental notes of its surroundings for use the following spring; 
but even man himself could not tell how certain birds’ nests were built 
merely by looking at them. The young bird, therefore, builds its first 
nest without ever having seen one made and with no other experience 
with nests than is implied by having lived in one. 
There can be no question that the impulse to build is as much the 
result of a physiological prompting as the impulse to mate which pre- 
cedes it, or the impulse to lay which follows it. Inherited habit directs 
the impulse in normal channels and, allowing for the range of individ- 
uality present in a greater or less degree in all birds, the bird, in its 
proper environment, selects a site and constructs a home after the man- 
ner of its species. When, however, the environment is changed and new 
conditions of site or material are introduced, the nest-building impulse, 
unchecked, and inevitably demanding an outlet, finds expression through 
new media. Possibly it is governed to some extent by intelligence, but 
any departure from type is usually an experiment, and the progressive 
individual pays the price or gains the reward of the pioneer by dire 
failure on the one hand, or exceptional success on the other. 
‘It is not unusual to observe evidences of sexual activity among 
birds in the fall—a mere reflection of the instincts of the nesting 
season—and among them is what might be called ‘play’ at site-hunt- 
ing and material gathering. So I have seen Tree Swallows, in August, 
investigate the openings in piles and pick up bits of dried grass only 
to drop them after a flight of fifty yards or more; and in this connection 
it is of significance to learn that they were all birds of the year (“Bird 
Studies with a Camera,” p. 103; see also Brewster, The Auk, 1898, p. 
194). 
Parasitism.—In « comparatively few cases, the instinct to build a 
nest is wanting, when the bird entrusts its egg to the care of another 
species, The European Cuckoo and our own Cowbird are examples of 
