6 Wild Birds 



young. The former nesting conditions are soon forgotten, while 

 the new are quickly adopted and defended with all the boldness 

 and persistence of which birds are capable. 



This method of studying birds depends mainly upon the 

 strength of the parental instincts which bind old to young by 

 an invisible chain, and upon the ease with which a bird learns 

 to adapt itself to new conditions. Upon more complete analy- 

 sis we' recognize the following psychological principles : 



(a) The strength of an instinct increases through exercise, and 

 may be reenforced or temporarily replaced by habit; 



(b) An instinctive impulse may be blocked or suppressed by 

 any stronger or contrary impulse ; 



(c) The instinct of fear is often temporarily suppressed by 

 the fighting instinct, or permanently overcome by the repetition 

 of any experience leading to the formation of new habits or 

 associations. 



We may also add: 



(d) New habits are readily formed and reenforce or supplant 

 those of older growth; 



(e) Abstract ideas, if they form any part of the furniture of 

 the average bird -mind, are extremely hazy and fleeting; 



(f) Finally 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. 



After a brief analysis of the parental instincts we will en- 

 deavor to show how the principles just given are applied to the 

 problem of approaching wild birds in the way described. 



The parental instincts begin to control the life of the adult 

 with the periodic revival of the reproductive functions, and vary 

 greatly in their scope and intensity at the different stages of 

 their reign as well as in different species of birds. They are 

 periodic, recurring at definite intervals during sexual life and 

 in serial form, one kind of act usually leading to the next in 

 sequence, and so on until the series is complete. 



When more than one litter is produced in a season, the 

 series of events is repeated with minor changes. If we include 



