?>-> LIFE-HISTORIES OF BIRDS 



and hairs constituting" the inner fabric. The perfect i 

 with which these articles are obtainable, and the entire ab- 

 sence of them in nests which are found in close proximity 

 to the residence of man, their places being supplied by fine 

 grasses, are facts which seem incapable of explanation. It 

 is true that the above articles being non-conductors of heat, 

 would retain the maternal warmth, and thus materially facili- 

 tate incubation ; while the lining of grasses, from its read\ 

 conductibility , would equally retard the operation. However, 

 a plausible theory can be given to account for this anomal- 

 ous condition of affairs. In its natural haunts, the forests, 

 feathers and hairs are still utili/ed in the lining of nests. 

 Being non-conductors of heat, they retain the warmth 

 imparted to them much longer than most vegetable substan- 

 ces. In situations remote from man's influence, the necess- 

 ity would doubtless sometimes arise for the female to quit 

 the nest while with eggs, to aid her partner in conquering 

 a common foe. During this absence, if not too protracted, 

 it is obvious that but little detriment would be experienced 

 by the developing embryo. Were the lining of a vegetable 

 character, but a few minutes of absence would suffice to chill 

 'the eggs, and destroy the vitality within. But in situations 

 contiguous to the residence of man, such molestations would 

 be of rare occurrence ; the necessity for vacating the nest by 

 the female, seldom, if ever, occurring. Consequently, the 

 mother-bird becomes a more constant sitter, and supplies 

 that uniformity of heat which is essential to germ-develop- 

 ment. That the upper surface of the egg receives more 

 heat than the lower, and is kept at a more uniform temper- 

 ture, is a truth that admits of no doubt. But this difficulty 

 is obviated by the mother-bird, who with true instinctive 

 feeling, turns and shifts the eggs at regular intervals, so that 

 the upper and lower surfaces shall receive their due propor- 

 tion of heat. Considerable experience in rearing poultry, 

 has taught us that incubation can be perceptibly shortened 



