Vol. xxxn 



1914 



] Strong, Habits of the Herring Gull. 179 



I made out of their sight, though they responded to various sharp 

 sounds or to a sudden shrill whistle by quick turns of the head. 



2. Visiial reactions. — Like practically almost all birds the Her- 

 ring Gull is predominately visual in its behavior. It also appears to 

 be unusually alert to visual stimuli. Rapid movements, especially, 

 are noticed as is the case with most seeing animals, so far as we 

 know anything of their reactions to visual stimuli. 



Standing outside of my tent, I could distinguish the form of a 

 man inside through the thin tent cloth, in certain positions with 

 reference to the sun's rays. Small portions of the man's figure 

 were also visible to me through narrow openings at the corners of 

 the tent. It does not seem probable to me that the gulls could fail 

 at least occasionally to get such glimpses for they often came 

 within a few feet of the tent and it was evidently under constant 

 scrutiny. Nevertheless, neither the gulls nor any other birds 

 appeared to notice these evidences of the presence of a man inside. 

 The visual images afforded under such circumstances were of course 

 of very low light intensity and of vague outline. They were also 

 very incomplete and often only small portions of a human form 

 would be even faintly visible. At any rate they seemed to lack the 

 intensity or completeness necessary for arousing the associations 

 connected with the appearance of a man in the open. 



On the other hand, I obtained some interesting evidences of 

 sensitiveness to very small visual stimuli under other circumstances. 

 In the course of my tent studies, I found a need for new openings 

 before the series of apertures which appears in Plate IV, Fig. 1, had 

 been prepared. A large pocket-knife blade was used for the pur- 

 pose, and the cloth was cut cautiously. On two occasions the knife 

 blade slipped through the cloth, unexpectedly, exposing a large 

 portion of its length. These occurrences were the causes of small 

 panics among a number of the gulls in the vicinity. The appear- 

 ance of a small portion of my hand through one of the corner 

 openings caused considerable excitement even when no rapid 

 movements were involved. 



I used my camera, however, at the openings with considerable 

 freedom after the first hour or so of quiet watching inside the tent. 

 The lens was often pushed partly through an opening without 

 arousing any significant disturbance. It was a dark object and it 



