PROGNE. 341 



been pillaged, a second outrage from the same source would soon 

 follow. The same prompting causes that bird to change its abode 

 from season to season, for, if the home were permanent^ it would 

 not long survive the encroachments of its enemies, and once dis- 

 covered, would immediately become a prey to repeated marauding 

 expeditions. On the other hand, there are certain birds, which, 

 because they build in protected localities, have no need to change, 

 and so, season after season and year after year, return to the same 

 spot to nest. 



" To such class belong the Martins. They have been protected 

 for hundreds of generations, first by tree holes and then by tlie 

 buildings of civilization. The instinct of protective change of 

 home has gradually become dormant and the hal)it — now nearly 

 an instinct — of permanency has became dominant, just as the 

 hobits of civilization dominate our own savage instincts, which 

 often burst forth in times of crisis. If repeatedly disturbed, the 

 birds wall change, often at terrible cost, as has been the case of 

 many of our own game birds, ducks, and even song birds, and the 

 old instinct of natural preservation against enemies, never really 

 absent — only dormant — becomes uppermost. They will learn 

 new habits with which to combat most effectivel} the new enemy, 

 and these habits, in turn, will finally become practically an instinct 

 to them. 



"But to return to our Martins; when I had destroyed the 

 second nest a few days later, they did not attempt a third, but 

 still continued to roost there each night. Penard tells us of taking- 

 four sets of eggs from the nest of a pair of these birds and still 

 they would not leave. In this instance the habit of living in one 

 place was supreme and clearly dominated the instinctive idea of 

 seeking a safer home. Undoubtedly the idea would become 

 uppermost if the jjersecutions kept up, 



" As has been said, individual habit and instinct are so closely 

 allied that it is hard to distinguish between them, but, neverthe- 

 less, there are certain points where the line may be drawn, of 

 instinct as subordinate to new habit. Thus the young Martins, in 

 spite of all their homing instincts, could not find their home until 

 they had determined, through repetition, in which of the four holes 

 it was located. Such knowledge was acquired only after many 

 trials or trips whereby a habit of arriving at the right point was 

 created. The results of the experiment with coloured eggs may 



