192 Strong, Habits of the Herring Gull. [April 



Island in Lake Superior, about one mile from Gull Island, where a 

 colony of gulls were breeding. In the latter part of the night just 

 before dawn, I heard the cries of gulls flying overhead. The night 

 had been very dark as the sky was clouded. 



Some observations on the nocturnal activities of Herring Gulls 

 have been reported by Schuster.^ He noted these birds feeding 

 on the river Mersey at Liverpool. Large quantities of food, thrown 

 into the river at night from ships, are stated to be responsible for 

 this nocturnal feeding. The gulls are described as flying and feed- 

 ing silently. 



Various writers speak of gulls "roosting" at night, and my cap- 

 tive gulls apparently sleep during the night, as a rule. It seems 

 probable that gulls usually rest during the night, except during 

 the breeding season or when food is especiall}^ available at night. 

 It is also probable that gulls are not active when the darkness is 

 intense. 



X. Variability and Modifiability in Behavior. 



According to Herrick ^ whose conclusions are in general supported 

 by my own observations : " The life of birds is one of instinct irradi- 

 ated by gleams of intelligence. Their mental faculties exhibit a 

 wide range of gradation from excessive stupidity to a fair degree of 

 intelligence with strong associative powers of things with ideas." 



In my study of the Herring Gull, I have been especially interested 

 in attempts at determining the extent of the "gleams," a fascinat- 

 ing but very elusive topic. The resourcefulness which animals show 

 in new situations and the extent to which their behavior may be 

 modified by new conditions may be considered fair criteria of their 

 intelligence. Variability in behavior, however, has some bearing 

 on the problem of intelligence. We must recognize perhaps two 

 types of variability in behavior which do not indicate intelligence 

 as it is commonly understood. They may even tend towards con- 

 fusion in our analyses of behavior, as acts which may seem to 



1 Schuster, W. Mowen als Nachtvogel. Zool. Beob. Frankfurt a. M. Jahrg. 47,' 

 No. 3, S. 79, 1906. 



2 The Home Life of Wild Birds. Revised Ed. 1905. G. P. Putnam's Sons, 

 p. 212. 



