HABITS OF THE HERRING GULL—STRONG. 495 
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, im 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 obtaimed 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 2, figure 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 cameras, however, at the openings with considerable free- 
dom 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 was moved 
slowly, whereas the shining steel of the knife blade came into view 
suddenly. 
In spite of the failure of the gulls to be disturbed by possible 
glimpses of the man inside the tent, there is abundant evidence that 
these birds see unusually well, as compared with most birds, in 
weak light. As will be discussed in the section of this paper which 
deals with the nocturnal activities of gulls, these birds are often 
active at night. My captive gulls if very hungry would eat in con- 
siderable darkness when their food was placed in a customary position, 
even when it was not easy for me to make out more than the bare 
outlines of the pieces of food. Thus on May 3, 1913, I fed my 
