BEHAVIOR OF VERTEBRATES 427 



where egg laying was brought about by stimulation of other 

 females, by stroking with the hand, by animals in distant cages. 

 He says: ' In so far as ovulation is dependent on environment 

 it is dependent, not upon any one afferent stimulus, but upon 

 the entire situation — involving the female's inborn disposition, 

 her whole past history and all the factors in the present environ- 

 ment which affect the social and emotional situation." 



On the observational side Sherman (53) gives a careful study 

 of the sparrow hawk. She discusses the nest life and the in- 

 stinctive activities concerned from the time of choosing the nest 

 to the flight of the fledglings. Bergtold (5) as a result of obser- 

 vations covering six years writes of the distribution, song, food, 

 mating, nests and nestlings of the house finch. 



Barrows (4a) relates a curious story of the concealing actions of 

 a bittern. The bittern assumes a characteristic attitude on 

 alighting. Its head, neck and legs are all in the same line and 

 its bill points to the sky. After holding this position for a few 

 minutes it relaxes, draws down its head and seeks for food. 

 Mr. Barrows had the interesting experience of seeing a bittern 

 in this rigid attitude. But the bird, when the cattail flags in 

 which it stood were swayed by a passing breeze, set up a similar 

 motion. The movement involved the whole body even the 

 legs. The observation was repeated and was confirmed by 

 another man. 



There are a few articles on bird migration. Phillips (44) 

 treats the subject from the standpoint of its periodic accuracy. 

 He gives facts and figures for a number of birds. For instance, 

 there are records of the return of the bobolink to Concord, 

 Mass., which cover a period of ten years. For this time the 

 average date is May 6 and the greatest deviation from this date 

 only six days. The journey which these birds take, he says, is 

 2000 miles in length and occupies two months, yet the average 

 error is only 9 per cent. The time of the return of the chimney 

 swifts has been kept in New Market, Va., for twenty-three years. 

 The average error is only 2.2 per cent. The author discusses 

 in a brief way the prevalent theories of migration: (a) the bio- 

 logical theory of distribution ; (b) the theory which makes migra- 

 tion a continuous movement and not a single flight due to a 

 migratory impulse; (c) the theory which makes the breeding of 

 tropical birds furnish the impulse for the northern migration 



