Birds, Beasts, and Bugs

E. R. Kalmbach.

Birds, mammals, and other vertebrates work constantly toward the natural suppression of insects. They may not always effect complete control, but they exert a steady and at times an emphatic local effect on insect populations. Farmers particularly do well to appreciate the help that birds give them.

Circumstances of the times led early research in economic ornithology and mammalogy into qualitative rather than quantitative channels. Most of the problems were approached with the idea of disclosing through stomach analysis the character of the food of birds and mammals; through a process of deduction an appraisal was made of the economic status of the creature involved. By far the greater part of our knowledge still is of this character, but keen observers through the years have encountered and appraised in the field instances of insect suppression that have been recorded quantitatively. Usually these recitals deal with local or temporary conditions, yet their frequency of occurrence under many diversified conditions gives indication of the possibilities.

To present this information one must resort to a compilation of published reports and in doing so I avail myself to a large extent of the contributions of W. L. McAtee, who more than anyone else has assembled information of this kind and whose philosophies with respect to bird-insect relations are classical.

McAtee always took pains to preface his dissertations on avian economics with words of caution regarding the nature and extent of benefits to be expected, as for instance :

"The general utility of birds in checking the increase of injurious animals and plants is well understood. It must be admitted, however, that while birds constantly exert a repressive influence on the numbers of the organisms they prey upon and even exterminate certain pests locally, they are not numerous enough to cope successfully with widespread invasions.

"Birds are prone to feed upon things that are abundant and easily accessible, for instance, in elderberry season a very large number of birds take elderberries; if May-flies swarm in a locality, practically all of the birds there devour May-flies. Thus, under unusual conditions, such as attend outbreaks of insects or other pests, birds may very naturally turn their attention to the plentiful and easily obtained food, and the attack on a particular pest often is intensified also by the flocking of birds from surrounding areas."

THE INSTANCES of insect suppression that I recite here are mere fragments from an abundant literature. I make no attempt to include illustrations even from all the major groups of insects or all the species of birds whose good work is on record.

Plagues of grasshoppers (locusts) have been recorded throughout the history of mankind. In our country one frequently encounters a recital of what was considered providential aid rendered by gulls in the control of the Mormon cricket in the early days of settlement in the Salt Lake Valley. Less heralded but no less significant have been the instances of grasshopper suppression by birds in the Midwest. An example was reported by Samuel Aughey in Nebraska.

He stated : "No Nebraskan will forget the countless number of young locusts that hatched out in the spring of 1875. Only where they were removed by causes known or unknown were crops produced during this season over the infested region. Among the few causes operating in the destruction of locusts during that period was the work of insectivorous birds. Among the spots that birds frequented was one on the west side of Salt Creek, not more than 2 miles from Lincoln. There was a small area of about 320 acres that harbored an immense number of locusts. The birds, however, made it one of their feeding grounds, and the locusts lessened daily in numbers. Within a month hardly a locust was left. Similar instances of the work of birds were observed farther down on Salt Creek and on Middle Creek.

"In the spring of 1877 ... on Middle Creek and its tributaries, and in various other places, I could see that the birds sensibly and radically diminished their numbers. One notable point was a few miles down Salt Creek from Lincoln. In May I visited the spot owing to the reported great numbers of locusts there. I estimated the number when I visited the place to be about 135 to a square foot. Already the birds had discovered it, and within sight were quail, larks, bobolinks, yellow-beads (blackbirds), plovers, curlews, and a few prairie chickens. With my glass I could see them picking up these insects. In a month hardly a locust was left in this place."

A more recent occurrence of bird control of an orthopterous insect closely related to the Mormon cricket was recorded by A. C. Burrill. He stated : "The State of Washington with the aid of agents of the United States Department of Agriculture, has been attempting to control the Coulee cricket, which devastates large areas in the vicinity of Adrian, Washington. According to Mr. Max Reeher, scientific assistant in the United States Bureau of Entomology, western meadowlarks appeared in great numbers in the Dry Coulee last fall and began eating the newly hatched crickets. So efficient were these birds in controlling the situation that arrangements for a 1919 control campaign were abandoned. The meadowlarks were almost entirely responsible for the complete cleanup of the area."

Appraisal of the effect of birds on insect populations often has been done by computing the amount of food eaten by the individual bird and then prorating this for the number of birds involved. Such an approach was used in judging the worth of the lowly English sparrow in Utah at a time when the alfalfa weevil was rising to ascendancy as a pest of this forage crop.

To quote from my comments on observations made in 1910 and 1911 in the Salt Lake Valley: "Parent birds (English sparrows) were timed for a period, usually an hour, and at the end of this time the incoming bird was captured and the contents of its bill and throat recorded. By taking the average of a number of such observations a fair idea was obtained of the amount of food brought daily to a brood of these young birds. . . . From this series of observations it appeared . . . that 15 larvae (of the alfalfa weevil) or their equivalent in bulk of other insects was a fair estimate of the amount of food brought in at each trip by the adult birds. It frequently greatly exceeded this amount."

On the basis of this amount of food being brought in on each of 11 trips an hour and on the assumption that the young were fed 12 hours a day, a single brood of English sparrows would account for 1,980 larvae or their equivalent of other insect food. At that time it was not uncommon to find farmyards with straw-thatched cattle sheds, which supported 100 or more nests of English sparrows. Such a colony of birds would devour a daily total of 198,000 alfalfa weevil larvae or other insect food. As the young remained in the nest for at least 10 days, they would have eaten insect food equal to the volume of 1,980,000 weevil larvae during their nestling life. Inasmuch as these birds were feeding on the larvae of the alfalfa weevil to about one-fourth of their food, it would appear that they were accounting for about 500,000 larvae. And this activity was representative of what occurred on a number of farms.

Were it possible to restrict the insect eating of wild birds to particular areas and to compare the results with other areas not frequented by birds, appraisal of the benefits would not be so difficult. At times, however, circumstances make it possible to measure visually the effect of insect destruction by birds.

Such an opportunity arose in connection with the earlier study of the relation of bird life to the alfalfa weevil. In that case, however it was not a wild but a domestic species, the chicken, that yielded the information. It came about in the following manner. Farmers in the Salt Lake Valley early became aware of the beneficial work done by young chickens and turkeys through their feeding on weevil larvae. By placing brooder houses for these birds in or near badly infested fields, not only were the insects reduced but the birds in turn acquired a substantial amount of needed food. After cutting the first crop of hay in a field of 15 acres, one farmer near Kaysville, Utah, set out three colony houses containing 100 chicks that were 8 weeks old, 90 that were 5 weeks old, and 160 that were 2 weeks old. The broods were moved from place to place in the field as the areas about the houses were cleaned of larvae. On June 29, 1911, the field was inspected; in the areas where the brooder houses had been removed, the second crop had responded rapidly and was from 9 to 10 inches high. At other points, far from the feeding chicks, there was no evidence of the second crop. At one point, where two brooder houses had been located for some time at a distance of several rods apart, circles of bright green indicated the area over which the young birds had removed enough of the larvae to permit growth of the second crop. Were it possible to restrict the feeding activities of wild birds in a like manner I have no doubt but that the benefits of their work would be equally apparent.

Woodpeckers long have been recognized as archenemies of wood-boring insect pests, and much has been written of these defenders of our forest resources. It is difficult, however, to appraise with certainty the benefits of this type of work in large forest areas to which the birds have unrestricted access. Yet some significant appraisals have been made locally.

Tom T. Torrel, of the Bureau of Entomology and Plant Quarantine, had this to say regarding an infestation of Engelmann spruce beetles in the Kootenai National Forest in Idaho:

"In 1937 a severe infestation of the Engelmann spruce beetle was reported to be depleting stands of spruce in the Pinkham Creek drainage on the Kootenai National Forest. . . . During the time of the second examination in June 1938, rather large groups of infested spruce were found with over-wintering brood. Woodpecker activity, however, had destroyed the brood to such an extent that the source of potential reinfestation was reduced to the protected brood below the snow line and it was predicted that very little reinfestation would occur."

Later comments on the same situation pointed out: "Woodpeckers had removed a large part of the bark from all trees above the snow line and it is believed that perhaps 75 to 80 percent, or even more, of the broods above snow line have been- destroyed. We have observed that woodpeckers concentrate upon the most heavily infested trees, which allows the greatest returns for their labor. . . ."

More recent reports of the beneficial work of woodpeckers in the suppression of spruce beetles have come from the White River National Forest in Colorado, where field representatives of the Department of Agriculture were quick to detect evidence of the good work. C. L. Massey and Frank T. Hutchison were convinced that "during the summer of 1947, woodpeckers were the most important natural enemy of the Engelmann spruce beetle in the area." Three species of woodpeckers were involved; many of the heavily infested trees were completely stripped of bark; and in those instances the "mortality of the brood approaches 100 percent. Even a slight amount of woodpecker work reduced the beetle population by more than half." It is hoped that such observations on an insect pest that is threatening much of the stand of Engelmann spruce may be continued and the full story of the role of the woodpeckers recorded.