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 a 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 



