172 THE POPULAR SCIENCE MONTHLY. 



myself to more congenial pursuits ! " Still another kind of molo- 

 thrus leads the life of a squatter, never building a nest of her 

 own, but brooding in the abandoned nest of some other bird. 



Many birds have, within the memory of man, made consid- 

 erable advances in architectural skill, and adoj^ted new and im- 

 proved methods of constructing their nests. This progress has 

 been observed especially in California since the settlement of that 

 country, and in all cases the young profit from the knowledge ac- 

 quired by their parents, and the improvement becomes a perma- 

 nent possession of the race. In places where they are particularly 

 exposed to the attacks of pugnacious sparrows, they have been 

 known to close the opening in front of their nests and make the 

 entrance on the back near the wall. In some instances this purely 

 precautionary and defensive change of structure, after its efficiency 

 had been tested in a single nest, has been adopted by the swallows 

 of an entire district. Orioles, according to the observations of Dr. 

 Abbott, finding that the bough from which they have suspended 

 their nest is too slight to sustain the weight of the full brood, at- 

 tach it by a long string to the branch above, fastening it securely 

 "by a number of turns and a knot." It would be difficult to say 

 in what respect the mental process leading to the adoption of such 

 a mechanical contrivance differs from that which causes an archi- 

 tect to buttress a weak wall. 



The Baltimore oriole also adapts the texture and structure of 

 its nest to the exigencies of climate. In the Southern States it 

 selects a site on the north side of a tree, and builds of Spanish 

 moss loosely put together and without lining, so as to permit a 

 free circulation of air. Farther north it seeks a sunny exposure, 

 builds more compactly, and uses some soft material for lining. 

 The impulse to build is instinctive, but conscious intelligence is 

 exercised in modifying the methods of building to suit circum- 

 stances. 



The same bird now uses yarn and worsted instead of vegetable 

 fiber for its nest, but it always selects for this purpose the least 

 conspicuous colors, such as gray and drab ; and yet the bird's gor- 

 geous plumage is proof, according to the theory of sexual attrac- 

 tion, that bright colors are pleasing to it. -Here we have an ex- 

 ample of eesthetic pleasure being subordinated to considerations 

 of safety; the prudent oriole, notwithstanding its fondness for 

 resplendent hues, choosing those colors which render its nest less 

 visible and more difficult to discover, and rejecting those which, 

 in other respects, are more gratifying to its fancy. 



The tailor-bird of East India used to stitch the leaves of its 

 nest together with fine grass, horse-hair, and threads, which it 

 twisted out of wool ; since the introduction of British manufact- 

 ures it uses sewing-thread and the filaments of textile fabrics, 



