other insect making up a larger percentage of food is the everpresent beetle. The individual records of meadowlarks show that the numbers of grasshoppers taken is very large as well as the percentage taken as food. From fifteen to thirty average-sized grasshoppers are usually consumed every four hours. Meadowlarks collected near Stockton, San Joaquin County, March to April, 1911, averaged nearly six grasshoppers apiece, thus showing a daily average of over seventeen. The same birds averaged ten crickets per day. Grain, weed seeds, and other insects made up the larger part of the food. A young meadowlark was fed 28 small grasshoppers (half an inch in length) at one meal. The capacity for the destruction of grasshoppers is therefore very great. The extent to which this capacity is used is dependent on the availability of the insect. Such is some of the evidence regarding the destruction of grasshoppers by birds in California. It allows of the conclusion that birds are really a significant agent in the destruction of these pests. It does not allow of the conclusion that they can be relied upon to limit their numbers below the point where damage can result. Man demands too great a readjustment of natural conditions to permit of complete dependence on the natural order of things. But because artificial means of controlling insect pests must be used, the value of a knowledge of the interrelations of organisms is in no way lessened. In a study of this kind we can at best but discover the more obvious relations between birds and insects. Occasionally we can. infer that certain interrelations exist which are not capable of being demonstrated by direct evidence. For instance: The failure of birds to check an insect outbreak after insects have appeared in abnormal numbers is evident to all. The success in preventing insects from becoming abnormally abundant is not apparent. In fact no absolute proof of their good work in this connection is obtainable. It must simply be inferred from data regarding the food of birds and their relation to insects when they appear in abnormal numbers, that the regulative influence exerted at times when normal conditions exist is just as important if not more important than their influence under abnormal conditions. It seems safe to conclude that the regulative influence exerted by birds keeps pace with the fluctuations of insect life. ON THE HABITS AND BEHAVIOR OF THE HERRING GULL, LARUS ARGENTATUS PONT. (Concluded.) BY R. M. STRONG. Plates XIX-XX. VII. REACTIONS TO STIMULI. 1. Auditory. I know of no experimental work on the reactions of gulls to sound stimuli, but I have made numerous observations in the field and with my captive gulls which show that hearing is reasonably keen in these birds, especially under certain circumstances. The bird shown in Plate VII, Fig. 2,1 was easily startled during the earlier part of my tent studies by the small though sharp noises made by the shutters of my cameras. During the course of the day, this gull became less and less sensitive to such noises and to other slight sounds which came from my tent, though one end of the tent was hardly five feet away. The responses finally consisted of little more than short turns of the head. A pistol shot from a boat fully a quarter mile away from shore caused a wild panic on the island. Little attention had been given to the boat before the shot was fired and boats could come nearer without causing a disturbance so long as no shooting occurred. On another occasion, the sharp noise made by a falling timber on the beach caused great alarm among gulls which could hardly have seen the fall. Great excitement was caused during the night of my stay on one of the Strawberry Islands by the noise produced by a falling board which was blown down from a position against my tent. It is improbable that many gulls if any could have seen this board fall. The resemblance of such noises to that made by the firing of a gun undoubtedly explains the intensity of the reactions. Many and perhaps all of the adult gulls had learned the significance of a gun shot. My captive gulls when tested by some simple experiments on Sept. 27 and 29, 1913, were not much disturbed by any noises which 1 See Auk, January, 1914. 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. Visual reactions.- Like practically almost all birds the Herring 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 purpose, 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 appearance 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 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 will eat in considerable darkness when their food is placed in a customary position, even when it is 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 gulls at about 8 P. M. The sky was clouded, and there was barely enough light to follow the movements of the birds from a position about fifteen feet away. The birds, which were thoroughly hungry, moved about somewhat uncertainly but they fed promptly from the two dishes in which their food was placed. When these birds were still partly in the nestling down plumage, on the evening of July 8, 1911, I made some notes on their movements at night. There was some light from the moon which was at half phase. I found the birds swimming or standing at the edge of the water in their enclosure, and they seemed to move easily in the semi-darkness. During even the darker portion of the night that I spent on Middle Strawberry Island, I had plenty of auditory evidence that both adult and young gulls were more or less active when it was too dark for me to see anything of the birds. The moon set about 1:00 A. M., and there was no light except that furnished by the stars. Adult birds were evidently flying occasionally, and juvenals were occasionally heard peeping. On many occasions, food has been brought to my captive gulls in paper wrappers. Often the package has been placed on the ground more or less completely open. When the paper is flapped by wind, the gulls show a good deal of apprehension. At one time they would not approach the package, although they could see that food was inside. They have become more accustomed to the flapping paper but have not entirely lost their fear of it. This experiment has been attempted only occasionally. Even when there has been no flapping paper, great distrust has been shown for the package, when the contents were covered by it though not entirely hidden. Under such circumstances, food is removed with slow and timid approaches followed by quick retreats. Flapping pieces of paper were for over a year very disturbing to the captive gulls, but after they had been fed daily for some weeks with food placed on a sheet of paper, their fear of moving paper decreased greatly. 3. Reactions to Chemical Stimuli.- During considerable portions of the time that I have had the captive gulls, I have conducted experiments on their reactions to chemical stimuli. A preliminary statement1 concerning the results of this work has already been published, and I plan to publish another fuller account later. In general, I may say here that I have found my captive gulls showing what I interpret as a dislike for pieces of liver that had been dipped in solutions of table salt or in weak acids. The following notes are extracted from my records of the first experiment. On July 11, 1911, I placed a number of pieces of herring in a strong solution of table salt in a pan just before feeding the gulls. Another pan contained similar pieces of herring without any salt. The birds were very hungry not having been fed since the previous evening. All three birds showed great aversion for the salted fish. Two ate of the salted food at once and the other joined them in a moment. The response was immediate, one bird disgorging what it had swallowed. Another dropped what it had taken, and the third swallowed only one piece. All three birds ran to water in less than a minute and drank heartily, though they had taken very little of the solution. They did not return to the food during twenty minutes that I waited. Experiments with other materials were carried on after this until Sept. 6, 1911, when a 10% solution of sodium chloride was employed. Pieces of liver were placed in the solution. The birds were exceedingly hungry and ate voraciously paying no attention to the salt solution. On Sept. 23, a 20% solution of common table salt was tried with pieces of liver. The birds were not so hungry at this time. One went to the dish containing the salt solution and picked up a piece of liver with the tip of its beak. After a few minutes of cautious manipulation of the liver it was taken into the bird's mouth only to be hurriedly ejected. The gull 1 Strong, R. M. 1912. The Sense of Taste in Birds. Science, N. S., Vol. XXXV, No. 911. June 14, p. 940. |