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POPULAR SCIENCE MOXTHLY 



but happily tliis ii= not the case. No harm need befall either old or 

 young. The former nesting site is soon forgotten, and the new quickly 

 adopted and defended with all the boldness and persistence of which 

 the birds are capable. 



This method of studying birds thus depends mainly upon the 

 strength of the parental instincts, and upon the readiness with which a 

 bird learns to adapt itself to new conditions. Upon more complete 

 analysis we recogiiize the following psychological principles, of which 

 the following are the most important: (a) The strength of an instinct 

 increases through its exercise, and may be reinforced by habit; (b) An 



Fig. 3. FiMALE Kingbird, astride Nest, shiei.dixg her Young from the Heat. 



instinctive impulse may be blocked or suppressed by any contrary im- 

 pulse; (c) The instinct of fear is often quickly suppressed by repetition, 

 or the formation of new habits. One might also add that: (d) New 

 habits are readily formed and may replace the old ones; (e) Abstract 

 ideas, if they form any part of the furniture of the average bird-mind, 

 are extremely hazy and fleeting; (f) Still further we must recall the 

 physiological fact that birds are guided in most of their operations 

 by sight and hearing, not by scent. Their olfactory organ is very 

 rudimentary at best, and avails them neither in finding food nor in 

 avoiding enemies. 



