372 FRANCIS H. HERRICK 



8. ORIGIN OF THE INSTINCTS OF INCUBATION .AND NIDIFICATION 



IN BIRDS 



In an earlier work we endeavored to show that the instinct to 

 hide supplemented by that of guarding the eggs was responsible 

 for the later instinct of incubation, where guarding with con- 

 cealment is effected in the same act.-** 



We have seen how the protection necessary to eggs, young 

 and adults has been secured, and how a proper nest may con- 

 tribute to this end. Incubation, arising in its initial stages 

 through the instinct to guard, and to conceal by covering with 

 the body, and later perpetuated and established, as we may 

 infer, by selection, in all probability long antedated any effective 

 nest-building. 



The most primitive nests undoubtedly belonged to w^hat 

 we have called the " secondary adaptive " type, mere holes 

 in the ground or in trees. Increment nests may have arisen 

 in the first instance through an earlier practise of collecting 

 materials of any description to cover the eggs upon leaving 

 them to look for food. All such would be scattered to some 

 extent upon re-entering the nest to cover and guard ; some, how- 

 ever, would remain to fomi a rude rampart or wall of circular 

 form, and this would be advantageous in holding the eggs to 

 a focal point. By the slight advantages thus gained, supple- 

 mented it may be, by a practice of drawing materials towards 

 the body while incubating, suggested by the present day actions 

 of certain gulls and terns, may have furnished a starting point 

 for the increment nest of the statant type. 



The exceptionally interesting breeding habits of the nutmeg 

 or Torres Straits pigeon (Myristicwora spilorrhoa), as described 

 by Banfield ^' at Dunk Island, Australia, offer further sug- 

 gestions upon this subject. This pigeon, we are told, breeds 

 on the island" during a period of four months, from the end of 

 September to the end of January, rearing two or three young, 

 one at a time, and that "for each successive egg a carpet of twigs 

 or leaves is spread." Those pigeons which "incubate on the 

 ground discard even the rude platform of twigs, which generally 

 represents the nest of those which prefer bushes and trees, but 

 gradually encircle themselves with tiny mounds of ejected seeds, 



^8 Home Life of ^^'ild Birds, p. 146. 



*'' Banfield, E. T. The Confessions of a Beachcomber. New York, 1909. 



