1

FOOD OF SPARROWS.

The following conclusions upon the relations of sparrows to agriculture are based upon the study of the food habits of a score of species, and have involved the examination of the contents of the stomachs of more than 4,000 individuals. These stomachs were collected during every month in the year from a large expanse of country, including practically all the States in the Union and the southern part of the Dominion of Canada.

MINERAL SUBSTANCES FOUND IN SPARROWS' STOMACHS.

Mineral matter plays a part in the digestion of sparrows and often amounts to one-tenth or one-quarter of the total contents of a stomach. These birds are preeminently seed eaters. Insectivorous birds with soft, weak bills and thin membranous stomachs could not possibly eat and digest a meal of tough, resisting seeds; but the hard, strong beaks and powerful, muscular gizzards of sparrows are admirably adapted to such a diet. Sparrows swallow the smaller seeds whole, but crack the larger ones. To aid digestion they pick up, while feeding, coarse bits of sand and tiny stones, which, in their mill-like gizzards, soon grind the seed material into a paste that can be as easily digested and assimilated as if it had been chewed by teeth. This mineral matter usually consists of angular white or pink pebbles of quartz from 2 to 5 mm. in diameter. Pieces of feldspar, tourmaline, mica, and even volcanic lava are sometimes found, and in Kansas the birds often utilize the disk-like sections of stems of fossil sea-lilies (Crinoideasee fig. 10). A sooty grouse taken in British Columbia had swallowed for this purpose four little nuggets of gold.2

FIG. 10.-Section of stem of fossil sealily.

FOOD IN GENERAL.

Of the food of sparrows, animal matter composes from 25 to 35 percent of the diet for the entire year, and vegetable matter from 65 to 75 percent. The animal food consists of insects and spiders and

The remainder of the native sparrows, which are mostly birds of more or less limited numbers or restricted distribution, are not considered in this bulletin, owing to lack of material for adequate study.

2 Forest and Stream, Vol. XXXIV. p. 431, 1890.

occasionally includes snails or millipedes; insects-mainly grasshoppers, beetles, and caterpillars-constitute more than nine-tenths. The vegetable food is composed almost entirely of seeds, although it also comprises a small quantity of fruit.

FOOD NEUTRAL IN EFFECT ON AGRICULTURE.

The neutral part of this food is made up principally of certain insects, spiders and snails, a small amount of wild fruit, and some seeds of useless plants. Insects form about four-fifths of the animal matter of the neutral part, comprising ants and certain kinds of flies and beetles. The flies, which are usually adult insects, but sometimes larvæ, include midges (Chironomidae), flies related to the housefly (Muscidae), March-flies (Bibionidae), and crane-flies (Tipulida). These insects never amount to 1 percent of the volume of the entire food of any species of sparrow for the whole year. May-flies (Ephemerida), emerging from the water by the million, are preyed on by the

sparrows that dwell in the immediate vicinity of streams or ponds. Ants seldom equal 2 percent of the volume of the year's food. Both typical ants (Formieidae) and myrmicids (Myrmicida) are taken. Such ants as Formica fusca and F. subsericia, Lasius, Myrmica, and Tetramorium are frequently selected. They are often eaten while yet in the winged state and are then caught in the air. Beetles of little or no economic importance amount to from 3 to 5 percent of the total volume of the food for the entire year. These are for the most part dung-feeding species belonging to the genera Aphodius (see fig. 11), Atenius, Onthophagus, and Hister. They are often found by hundreds in cow droppings in pastures.

FIG. 11.-Dung-beetle (Aphodius) (loaned by Prof. S. A. Forbes).

The remainder of the neutral part of the food is made up of spiders and snails. Spiders, though predatory, have not as yet been classed as useful, because, as already stated, as a group they seem to destroy about as many beneficial as injurious insects. The kind most frequently eaten by sparrows are the running ground-spiders, which, though probably more useful than harmful, are of too little importance to be classed otherwise than as neutral. They constitute 1 to 3 percent of the food. A few snails are eaten. These are as a rule not injurious; and though an exception should be made of the pond snail (Lima), which acts as intermediate host to the liver fluke, a pest to sheep raisers, probably very few if any of these are included among the small number of snails actually eaten, and they may be disregarded,

FOOD INJURIOUS IN EFFECT ON AGRICULTURE.

The injurious part of the food of sparrows, the removal of which tends to cause a harmful effect upon crops, is made up of useful insects and spoils from cultivated crops, such as grain and fruit. Beneficial insects seldom amount to more than 2 percent of the food. They consist mostly of enemies of insect pests and a very few flowerfertilizing species, such as certain wasps and some small bees of the genera Andrena and Halictus. The insect enemies are either ground-beetles (Carabidae) or parasitic wasps. The particular groundbeetles selected belong to the less useful predatory kinds. They are small species, the exact economic position of which is not yet known, and include Amara, Anisodactylus, Agonoderus, Bembidium, and the smaller species of Harpalus. One species-Agonoderus pallipeshas been found injurious to grain, and in time it and some other slightly carnivorous carabids may become pests like the related Zabrus gibbus of Europe. The parasitic Hymenoptera include such wasps as the smaller Ichneumonidæ, the larger Braconidæ, and Scoliide of the genera Myzine and Tiphia. But the quantity of useful insects eaten by sparrows is small; omitting those taken by the English and field sparrows, it is insignificant. And though 4 percent of the food of the latter consists of useful insects-a larger percentage than is attained by any other member of the sparrow family-yet this record is very favorable compared with those of many birds. The loggerhead shrike and the king-bird, for example, take 12 percent and 20 percent, respectively, of their food in beneficial insects, and there are other birds whose records are still less creditable.

Cultivated fruit forms no significant part of the food of sparrows. The white-crowned sparrow occasionally punctures a few grapes in the East; the English sparrow adds more or less fruit destruction to his many other sins; and it is probable that one or two western species do some little damage of this kind: but with these exceptions the sparrow family is harmless to orchard and vineyard.

The English sparrow does so much damage to grain that it is considered a pest, and the native sparrows might naturally be suspected of having similar habits; but though they frequently sample grain in stubble-fields, they have not as yet been found committing serious depredations. In order to compare the grain-eating propensities of the various species, specimens were collected on a farm a few miles south of Washington, D. C., before and after the wheat was cut. Of nineteen native birds, representing song, field, chipping, and grasshopper sparrows, only two had eaten grain, and these had taken only one kernel each, while, on the other hand, of five English sparrows that were examined every one was gorged with wheat. On this particular farm flocks of English sparrows pillage the wheat crop from the time it comes in milk until it is threshed; and attack corn in

the roasting-ear stage, and feed on it from the time it is put in the crib until wheat comes in the milk again in June. There is scarcely a grain that they do not injure, while with the native sparrows the reverse seems to be true. The latter eat a little grain, but seldom does it amount to more than 5 percent of the year's food, a modest fee for their service when it is considered that the meadowlark, one of the best birds of the farm, takes 13 percent of its food in grain, the crow 35 percent, and the crow blackbird 47 percent.

The most serious charge that can be brought against sparrows is that they distribute noxious plants, the seeds of which pass through their stomachs and germinate when voided from the body; and this, though not strictly germane to the subject under consideration, will be treated of here as the most appropriate place. Sparrows do not distribute catbrier, poison sumach, and poison ivy, as do many birds, but it is probable that they do, to a certain extent, disperse the seeds of such weeds as amaranth, gromwell, and spurge. However, it seems likely that this agency of seeding down farms to weeds is infinitesimal when compared with the dispersion of weeds caused by the use of manure containing weed seed and the planting of impure seed, which often contains seeds of foreign weeds of the worst stamp. The digestive apparatus of sparrows has the power to crack or crush the seeds of crab-grass, pigeon-grass, pigweed, lamb's-quarters, and most other seeds, including the hard drupes of the blackberry. I have examined thousands of stomachs of sparrows containing ragweed, and have never found an unbroken seed. The outer ribbed shell of the akene is cracked and not swallowed, but parts of the, true seed coat in the shape of angular fragments 3 to 5 mm. long, which are dirty gray externally and greenish white internally, are usually found during stomach examination. Uncrushed cotyledons are seldom met with. These facts, which hold also when seeds of wild sunflowers and polygonums are eaten, seem to preclude the possibility of subsequent germination. Concerning the likelihood of the germination of the seeds of weeds that are grasses it may be stated that time and again tree sparrows which have fed on pigeon-grass have been examined, and it has been found that while their gullets contained from 100 to 300 whole pigeongrass seeds with the inner glumes removed, the gizzards were filled with a pasty mass of endosperm containing not more than a dozen whole seeds. But with the harder, smaller seeds the possibility of germination is better. The digestive organs, although they have the power of cracking such seeds, nevertheless occasionally allow some to pass out in a perfect condition, as was shown by an experiment with a captive song sparrow in which amaranth seeds were voided uninjured and germinated very well. Birds take seeds for food, however, and it seems probable that such use would preclude the evacuation of any but a most insignificant proportion of uninjured seeds.

FOOD BENEFICIAL IN EFFECT ON AGRICULTURE.

The beneficial part of the food of sparrows is made up of insect pests and the seeds of weeds. Insect pests amount to from 10 to 20 percent of the year's food, and are for the most part grasshoppers (Acrididæ and Locustida), caterpillars, principally Noctuidæ (that is, cutworms, army worms, and their allies) and some Geometridæ, such as cankerworms and their allies, and beetles of various families-Chrysomelidæ or leaf-beetles, Elateridæ or click-beetles, and Rhynchophora or weevils. Conspicuous among the genera of beetles met with in stomachs of birds are Systena, Epitrix, Odontota, Limonius, Drasterius, Sitones, and Phytonomus. Bugs are eaten to an unimportant extent, and constitute about 1 percent of the food. The plant-feeding forms include such Heteroptera as some of the smaller soldier bugs (Pentatomidae), leaf-bugs (Capsida), a few such Homoptera as leafhoppers (Jassidæ), and in very rare instances plant-lice (Aphididæ). Insects seldom form more than a third of the food of adult sparrows for the year, but their nestlings are practically entirely insectivorous; on which account these birds, in raising from two to three broods a season among agricultural crops, do their greatest good as destroyers of insect pests by cramming countless numbers of caterpillars and grasshoppers down the throats of their ravenous young. Some grasshoppers are much more injurious than others. The most destructive species is the Rocky Mountain locust (Melanoplus spretus-see fig. 12), which at intervals invades the plains of the central United States in such numbers as to actually hide the sun. These insects travel onward, sweeping away every vestige of green vegetation in their path, and bringing destruction and desolation to thousands of farms. As shown by the investigations of Prof. Samuel Aughey in Nebraska, the native sparrows perform a useful part in aiding to check these invasions.

FIG. 12. Rocky Mountain locust (after Riley; loaned by Division of Entomology).

In studying the efficiency of birds in checking an uprising of the cankerworm (Anisopteryx vernata) in Illinois, Prof. S. A. Forbes collected birds in a bearing apple orchard which had been so injured by the worms for several years that it looked as though it had been swept by fire. Among these birds were the grasshopper sparrow, the chipping sparrow, the field sparrow, and the dickcissel. The examination of their stomachs showed that although cankerworms were not eaten by the grasshopper sparrow, they amounted to 163 percent of the food of the chipping sparrow, 234 percent of that of the field sparrow, and 43 percent of that of the dickcissel. Nearly all spar

1 First Ann. Report U. S. Entomological Commission, App. II, pp. 29-32, 1878. * Bull. Ill. State Laboratory Nat. Hist., Vol. I, No. 6, p. 12, 1883.

2