PROGNE. 339 



• 



directly to the proper spot, but first tried several holes as on the 

 first day of departure. At length, after many trips, the proper 

 method o£ 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 iictions 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 present, evidence showed that young birds 

 with undeveloped intellect, ignorant of the life struggle before 

 them, even though homing instinct was predominant, were able, 

 only by repeated trials, to recognise their home among several 

 others of similar appearance. Similarly their parents, upon first 

 taking possession, had carried straw 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 dis- 

 covering their mistake. At length, after many trips, they became 

 so used to the, proper location that no further errors were made. 

 Thus, even they were dependent upon a habit, to point out their 

 permanent home ; a habit credited by repeated trials through 

 .which sense of exact location became, at length, indelibly fixed 

 upon their brains. 



" The nest containing the three eggs in question, though placed 

 out of any direction rays of the sun, was exposed to the light of 

 day, so that the eggs were in plain view of the parent bird when 

 approaching tho nest. One day, I carefully marked the eggs 

 with blotches of red ink, leaving uncoloured 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 hesitatingly crouched upon them and the incubation 

 proceeded as if nothing had occurred. 



" The following day 1 removed both nests and eggs, putting 

 them in a prominent spot, only a few feet away from their 

 original resting place. The parent bird, disturbed by my efforts, 

 flew excitedly about, and, the instant I left the ladder, flew to 



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