GREY BREASTED MARTINS 337 



but first tried several other holes as on the first day of depar- 

 ture. At length, after many trips, the proper method of 

 approach suddenly dawned upon their consciousness, and 

 thereafter they made it with unerring skill. 



At that time there was, under the house, a second nest 

 with three slightly incubated eggs, which I thought might 

 be put to some use. By watching the other birds I realized 

 that many actions were the result of newly acquired habits, 

 and therefore might be influenced by outside agencies. How 

 far, though, did these habits control instinct ? Up to the pres- 

 ent, evidence showed that young birds with undeveloped in- 

 tellect, ignorant of the life struggle before them, even though 

 homing instinct was predominant, were able, only by repeat- 

 ed trials, to recognize their home among several others of 

 similar appearance. Similarly their parents, upon first tak- 

 ing possession, had carried straws to each of the four holes 

 until they discovered that four nests were building instead 

 of one; even then they would often carry to the next hole 

 before discovering their mistake. At length after many 

 trips, they became so used to the proper location that no fur- 

 ther errors were made. Thus, even they were dependent 

 upon a habit to point out their permanent home ; a habit cre- 

 ated by repeated trials through which the sense of exact lo- 

 cation became, at length, indelibly fixed upon their brains. 



The nest containing the three eggs in question, though 

 placed out of any direct rays of the sun, was exposed to the 

 light of day, so that the eggs were in plain view of the par- 

 ent, when approaching the nest. One day, I carefully 

 marked the eggs with blotches of black ink, leaving uncolored 

 the large ends with their air chambers, and placed them back 

 in the nest as nearly as possible in the same old position. At 

 first the martins were much excited and looked at the eggs 

 askance, peering this way and that, as if they might find 

 the lost originals hidden away in some darkened corner. In 

 a few minutes, however, deciding that, though they did look 

 different, they were still the same eggs, one of the birds hesi- 



