NESTS AND NEST-BUILDING IN BIRDS 183 



a true nest, though not necessarily of the most primitive type, 

 even though their young never see their parents, and according 

 to our view the nest-building instinct is wanting only in such 

 birds as regularly make no preparations, or take no precautions 

 to conceal or protect their eggs except through the aid of their 

 own bodies or instincts. The ocellated Megapode {Lipoa ocel- 

 lata), indeed, is known to prepare its nest with great care, and 

 with a precision and uniformity hardly exceeded by builders 

 of a higher order. A shallow depression is first scratched in the 

 ground to a depth of eight or nine inches, with diameter twice 

 as great, and the cup or saucer thus formed is filled with an 

 overflowing mass of dead leaves and grass; upon this low pile 

 the soil is finally heaped into a fairly even mound. Their large 

 eggs, which are laid at rather long intervals, are regularly set 

 in the same plane, and with their smaller ends turned down, 

 around and within the " rim of the saucer," and but a few 

 inches above the bed of fermentable leaves, first at opposite 

 sides in form of a lozenge, and then in the interstices, until 

 a circle of eight eggs is complete, all standing in the same plane, 

 and with large ends up ; at each laying this mound is successively 

 opened at the top, and the hole as often filled in with sand. 



By secondarily adaptive nests (No. 2 of table 2), we mean 

 any natural cavities used, with little or no change, for the con- 

 cealment and protection of the eggs or young, and we regard 

 them as the most primitive form of existing nests. In all such 

 cases there are the instincts to conceal and otherwise protect, 

 through choice of site, acts which lie at the foundation of all 

 nest-building operations in birds ; although such individuals may 

 use no materials gathered from without, their chosen protective 

 cavities, so far as instinct is concerned, must be regarded as 

 adaptive nests. In many cases they are adopted without change 

 (A^o. 2, a^) but in other species they are quite as apt to be pri- 

 marily adapted to the needs of the occupant by a greater or less 

 amount of constructive effort (No. 2, b'), and even by many 

 species which under other circumstances excavate or put to- 

 gether the entire fabric themselves. 



The third and highest class of nests, which naturally claim 

 our chief interest (No. j of table 2), are those which are pri- 

 marily adaptive, or made to fit the needs of the builders, solely by 

 their own efforts, through the aid only of such supports as nature 



