1913 ' Phillips, Migration and Periodic Accuracy. 1 Jo 



likely analogous in 8 certain way to evolution of form, which as 

 embryology shows us so well, is forced into t he repetil ion of ancient 



and disused types. 



Professor Wheeler in his book on ants gives a very concise 



discussion of instinct, with some excellent definitions. He points 



out various grades of degenerating instincts in these animals, some 



of which can be brought hack into activity under proper conditions. 



According to him, instinct, "the combination of complexity with 

 automatic lixity," has been studied from lour different points of 

 view, ethological, physiological, psychological and metaphysical. 



We arc naturally concerned now mostly with the physiological 

 side. 



We must hear in mind that the regularity of instinctive behavior 

 has probably been somewhat exaggerated, and as Jordan says, an 

 instinctive action is subject to variation like all other characteristics 

 of animals. 



Individual birds show peculiarities of behavior in nest building, 

 sonj, r and other actions. Hodge has shown that a great difference 

 in power of orientation exists for homing pigeons. Also, in animals 

 as high in the scale of life as birds, there cannot fail to he some 

 "power of choice" in almost every stereotyped activity. 



This brings us hack to our enquiry into the mechanism by which 

 birds are enabled to arrive each year at a given locality at almost 

 exactly the same time. From a physico-chemical standpoint the 

 accuracy of time sense in certain species is little short of marvelous 

 and is well shown in the familiar Baltimore Oriole and the Bobolink, 

 which are both late arrivals in the north. Mr. Brewster very 

 kindly allowed tne to see his notes on the arrival of these species 

 at Concord, Massachusetts, for long periods of time. From L900 

 to Mil I his earliest record for the Bobolink is May 'J, and his latest 

 May II. For three years the arrival was May 8, and for two 

 years May 7; the average being May 7. Just as remarkable is 

 the Oriole at Concord. From 1000 to 1011, the earliest is May 3 



and latest May I I. The average is May 8, and the species appeared 



twice on this day, twice on the 0th, once on the 7th, and once on 



the 6th. An earlier period including the years '86, '89, '90, '01 



and '93, gives the average date of the Oriole near Boston as May It, 

 with the greatest variation at six days. 



