SOME COMMON BIRDS USEFUL TO THE FARMER
by F. E. L. Beal, Farmers’ Bulletin 630, USDA, February 1915
Whether a bird is beneficial or injurious depends almost entirely upon what it eats. In the case of species which are very abundant, or which feed to some extent on the crops of the farmer, the question of their average diet becomes one of supreme importance, and only by stomach examinations can it be satisfactorily solved. Field observations are at best but fragmentary and inconclusive and lead to no final results. Birds are often accused of eating this or that product of cultivation, when an examination of the stomachs shows the accusation to be unfounded. Accordingly, the Biological Survey has conducted for some years past a systematic investigation of the food of those species which are most common about the farm and garden.
Within certain limits birds eat the kind of food that is most accessible, especially when their natural food is scarce or wanting. Thus they sometimes injure the crops of the farmer who has unintentionally destroyed their natural food in his improvement of swamp or pasture. Most of the damage done by birds and complained of by farmers and fruit growers arises from this very cause. The berry-bearing shrubs and seed-bearing weeds have been cleared away, and the birds have no recourse but to attack the cultivated grain or fruit which has replaced their natural food supply. The great majority of land birds subsist upon insects during the period of nesting and molting, and also feed their young upon them during the first few weeks. Many species live almost entirely upon insects, taking vegetable food only when other subsistence fails. It is thus evident that in the course of a year birds destroy an incalculable number of insects, and it is difficult to overestimate the value of their services in restraining the great tide of insect life.
In winter, in the northern part of the country, insects become scarce or entirely disappear. Many species of birds, however, remain during the cold season and are able to maintain life by eating vegetable food, as the seeds of weeds. Here again is another useful function of birds in destroying these weed seeds and thereby lessening the growth of the next year.
In the following pages are discussed the food habits of more than 50 birds belonging to 12 families. [We are featuring four of the 50 in this issue, ed.] Many are eastern forms which are represented in the West by slightly different species or sub-species, but unless the food habits differ they are not separately described. In some cases specific percentages of food are given, but for the most part the statements are made without direct reference to the data on which they are based.
The eastern bluebird (Sialia sialis shown in Fig. 1), one of the most familiar and welcome of our feathered visitors, is a common inhabitant of all the States east of the Rocky Mountains from the Gulf of Mexico to southern Canada. In the Mississippi Valley it winters as far north as southern Illinois, and in the East as far as Pennsylvania. It is one of the earliest northern migrants, and everywhere is hailed as a harbinger of spring. Very domestic in habits, it frequents orchards and gardens, and builds its nests in cavities of trees, crannies in farm buildings, or boxes provided for its use.
The bluebird has not been accused, so far as known, of stealing fruit or of preying upon crops. An examination of 855 stomachs showed that 68 per cent of the food consists of insects and their allies, while the other 32 per cent is made up of various vegetable substances, found mostly in stomachs taken in winter. Beetles constitute 21 per cent of the whole food, grasshoppers 22, caterpillars 10, and various other insects 9, while a number of spiders and myriapods, about 6 per cent, comprise the remainder of the animal diet. All these are more or less harmful, except a few predacious beetles, which amount to 9 per cent. In view of the large consumption of grasshoppers and caterpillars we may at least condone this offense, if such it may be called. The destruction of grasshoppers is very noticeable in August and September, when these insects make up about 53 per cent of the diet.
It is evident that in the selection of its food the bluebird is governed more by abundance than by choice. Predacious beetles are eaten in spring, as they are among the first insects to appear; but in early summer caterpillars form an important part of the diet, and these are later replaced by grasshoppers. Beetles are eaten at all times, except when grasshoppers are more easily obtained.
So far as its vegetable food is concerned the bluebird is positively harmless. The only trace of any useful product in the stomachs consisted of a few blackberry seeds, and even these probably belonged to wild rather than cultivated varieties. Following is a list of the various seeds which were found: Blackberry, chokeberry, juniperberry, pokeberry, partridgeberry, greenbrier, Virginia creeper, bittersweet, holly, strawberry bush, false spikenard, wild sarsaparilla, sumac (several species), rose haws, sorrel, ragweed, grass, and asparagus. This list shows how little the bluebird depends upon the farm or garden to supply its needs and how easily by encouraging the growth of some of these plants, many of which are highly ornamental, the bird may be induced to make its home on the premises.
Two species of bluebirds inhabit the Western States—the mountain bluebird (Sialia currucoides) and the western bluebird (Sialia mexicana subspecies). In their food habits they are even more to be commended than their eastern relative. Their insect food is obtainable at all times of the year, and the general diet varies only in the fall, when some fruit, principally elderberries, is eaten, though an occasional blackberry or grape is also relished. In an examination of 217 stomachs of the western bluebird, animal matter (insects and spiders) was found to the extent of 82 per cent and vegetable matter to the extent of 18 per cent. The bulk of the former consists of bugs, grasshoppers, and caterpillars. Grasshoppers, when they can be obtained, are eaten freely during the whole season. Caterpillars also are a favorite food and are eaten during every month of the year; March is the month of greatest consumption, with 50 per cent, and the average for the year is 20 per cent. Two stomachs taken in January contained 64 and 50 per cent, respectively, of caterpillars, Beetles also are eaten and comprise mostly harmful species.
The vegetable matter consists of weed seeds and small fruits. In December a few grapes are eaten, but elderberries are the favorites whenever they can be found. It is only when these are in their greatest abundance that vegetable exceeds animal food.
Seven common species of swallows are found within the limits of the United States, four of which have abandoned to some extent their primitive nesting habits and have attached themselves to the abodes of man.
In the eastern part of the country the barn swallow (Hirundo erythrogastra shown in Fig. 2) now builds exclusively under roofs, having entirely abandoned the rock caves and cliffs in which it formerly nested. More recently the cliff swallow (Petrochelidon lunifrons) has found a better nesting site under the eaves of buildings than was afforded by the overhanging cliffs of earth or stone which it once used and to which it still resorts occasionally in the East and habitually in the unsettled West. The martin (Progne subis) and the white-bellied, or tree, swallow (Iridoprocne bicolor) nest either in houses supplied for the purpose, in abandoned nests of woodpeckers, or in natural crannies in rocks. The northern violet-green swallow, (Tachycineta thalassina), the rough-winged swallow, (Stelgidopteryx serripennis), and the bank swallow (Riparia riparia) still live in practically such places as their ancestors chose.