Food Habits of the Thrushes of the United States

(Hylocichla ustulata swainsoni and Hylocichla ustulata ustulata.)

The olive-backed thrush and its relative, the russet-backed, occupy the whole of the United States at some time during the year. The olive-back breeds north of our northern border, except in the higher mountains, and the russet-back on the Pacific coast nests as far south as southern California. The habits of birds of this species resemble those of others of the genus in living in swamps and woodlands rather than in gardens and orchards. The russet-back on the Pacific coast, however, seems to have become quite domestic, and wherever a stream runs through or past an orchard or garden, or the orchard is near thick chaparral, this bird is sure to be found taking its toll of the fruit and rearing its young in the thicket beside the stream. During the cherry season it takes a liberal share of the fruit, but its young, then in the nest, are fed almost entirely on insects. The eastern subspecies, on the contrary, does not come in contact with domestic fruit or any other product of husbandry. A great number of the subspecies nest far north of the region of fruit raising.

For this investigation 403 stomachs of the olive-backed thrush were available, collected in 25 States, the District of Columbia, and Canada. Florida, Louisiana, and Texas represent the most southern collections and New Brunswick, Ontario, and Northwest Territory the most northern. In California 157 stomachs were obtained, which, with those taken in Oregon and Washington, fairly represent the Pacific coast region. The whole collection was fairly well distributed over the nine months from March to November. The food consisted of 63.52 per cent of animal matter to 36.48 per cent of vegetable.

Animal food.– Beetles of all kinds amount to 16.29 per cent. Of these 3.14 per cent are the useful Carabidæ. The others belong to harmful or neutral families. Weevils or snout-beetles (Rhynchophora) amount to 5.29 per cent, a high percentage for such insects. One Colorado potato beetle (Leptinotarsa decemlineata) was found in a stomach taken on Long Island. Hymenoptera collectively aggregate 21.50 per cent. Of these, 15.20 per cent are ants – a favorite food of Hylocichla. The remainder (6.30 per cent) were wild bees and wasps. No honeybees were found. Caterpillars, which rank next in importance in the food of the olive-back, form a good percentage of the food of every month represented and aggregate 10.30 per cent for the season.

Grasshoppers are not an important element in the food of thrushes, as they chiefly inhabit open areas, while Hylocichla prefers thick damp cover, where grasshoppers are not found. An inspection of the record shows that most of the orthopterous food taken by the olive-back consists of crickets, whose habits are widely different from those of grasshoppers, and which are found under stones, old logs, or dead herbage. The greatest quantity is taken in August and September. The average for the season is 2.42 per cent.

Diptera (flies) reach the rather surprisingly large figure of 6.23 per cent. These insects are usually not eaten to any great extent except by flycatchers and swallows, which take their food upon the wing. The flies eaten by the olive-back are mostly crane flies (Tipulidæ) or March flies (Bibio), both in the adult and larval state. Crane flies are slow of wing and frequent shady places. The larvæ of both groups are developed in moist ground, and often in colonies of several hundred. With these habits it is not surprising that they fall an easy prey to the thrushes.

Hemiptera (bugs), a small but rather constant element of the food, were found in the stomachs collected every month, and in July reach 11.11 per cent. They were of the families of stinkbugs (Pentatomidæ), shield bugs (Scutelleridæ), tree hoppers (Membracidæ), leaf hoppers (Jassidæ), and cicadas. Some scales were found in one stomach. The total for the season is 3.76 per cent. A few insects not included in any of the foregoing categories make up 0.48 per cent of the food. Spiders, with a few millipeds, amount to 2.22 per cent, the lowest figure for this item of any bird of the genus Hylocichla. Snails, sowbugs, angleworms, etc. (0.32 per cent), complete the animal food.

Following is a list of insects identified and the number of stomachs in which found:

This list of insects contains a considerable number of injurious species and some that at various times and places have become decided pests. Such are the Colorado potato beetle (Leptinotarsa decemlineata), the spotted squash beetle (Diabrotica soror), the cloverleaf weevil (Phytonomus punctatus), and the various species of Lachnosterna, the parent of the destructive white grubs. Many others are plant feeders and may increase to such an extent as to inflict great damage upon agriculture.

Vegetable food.– The vegetable food of the olive-backed thrush consists of small fruit. The bird has a weak bill and can not break through the tough skin of the larger kinds. In the cherry orchards of California the writer many times observed the western subspecies of this bird, the russet-back, on the ground pecking at cherries that had been bitten open and dropped by linnets and grosbeaks. Blackberries and raspberries have a very delicate skin and are successfully managed by weak-billed birds, so that all the records of domestic fruit eaten by the eastern form relate to these berries, and it is probable that in most cases the fruit was not cultivated. The total of cultivated fruit for the season is 12.63 per cent of the whole food, but if we consider the eastern subspecies alone this item would practically disappear. Wild fruit (19.73 per cent) is eaten regularly and in a goodly quantity in every month after April. Weed seeds and a few miscellaneous items of vegetable food (4.04 per cent) close the account.

Following is a list of vegetable foods so far as identified and the number of stomachs in which found.

Food of young of russet-backed thrush.– Before concluding the discussion of this species it will be of interest to note the results obtained from an investigation of stomachs of 25 nestlings of the russet-back taken in June and July when the birds were from two to eleven days old. These were from eight broods, ranging from three to five nestlings to the brood. The percentage of animal food of the young (92.60 per cent) is considerably higher than that of the parent birds.

The distribution of the animal food is as follows: Caterpillars were found in every stomach but seven and aggregated nearly 27 per cent; beetles, including the useful Carabidæ (7.7 per cent), are irregularly distributed to the extent of 22 per cent; other more or less harmful species included five families of (Hemiptera) bugs, 13.8 per cent, viz, stinkbugs, leaf hoppers, tree hoppers, shield bugs, and cicadas; ants and a few other Hymenoptera amount to 12 per cent, and spiders the same. These latter were mostly harvestmen or daddy longlegs (Phalangidæ). The remainder (6 per cent) included a few miscellaneous insects. Only three stomachs contained remains of grasshoppers. Carabid beetles were eaten by the young birds to the extent of 7.7 per cent, which is more than three times the amount eaten by the adults, a remarkable fact when is considered that these insects are very hard shelled, thus seemingly unsuited for young birds.

The vegetable food consisted of fruit (6.8 per cent), mainly blackberries or raspberries, found in 11 stomachs, and twinberries in 1, and two or three other items, including a seed of filaree and some rubbish. From the irregular variety of food in the different stomachs, it would seem that the parents make little selection, but fill the gaping mouths of their young with the nearest obtainable supply.

In addition to the examination of stomach contents of nestlings two nests were carefully and regularly watched, and from these it was determined that the parent birds fed each nestling 48 times in 14 hours of daylight. This means 144 feedings as a day's work for the parents for a brood of three nestlings, and that each stomach was filled to its full capacity several times daily, an illustration that the digestion and assimilation of birds, especially the young, are constant and very rapid. Experiments in raising young birds have proved that they thrive best when fed small quantities at short intervals rather than greater quantities at longer periods. Aside from the insects consumed by the parents, a brood of three young birds will thus each require the destruction of at least 144 insects in a day and probably a very much greater number.

Summary.– In a résumé of the food of the olive-backed and russet-backed thrushes one is impressed with the fact that they come in contact with the products of industry but rarely. The olive-back's food habits infringe upon the dominion of man but little. The bird lives among men, but not with them. The western form, the russet-back, comes more into relations with the cultivated products because it visits orchards and partakes freely of the fruit. Even then the damage is slight, as much of the fruit eaten is that fallen to the ground. Moreover, while the adult bird is feeding upon fruit a nestful of young are being reared upon insects which must be largely taken from the orchard, thus not only squaring the account but probably overbalancing it in favor of the farmer.

HERMIT THRUSHES

(Hylocichla guttata subspp.)

The hermit thrush of the subspecies H. g. pallasi inhabits the Eastern States in winter as far north as Massachusetts and breeds from the mountains of Maryland and Pennsylvania and from northern Michigan and central Minnesota northward to Alaska. Several other subspecies occupy the Pacific coast region in suitable localities – that is, in the higher and more wooded sections, as this bird, like all of the genus Hylocichla, does not live in treeless or arid regions. In the East the bird is a late fall migrant and may often be seen sitting silent and alone on a branch in the forest in late October or even in November, when the great army of migrants have passed on to the South. While a beautiful songster, the species is so quiet and unobtrusive that by sight it is entirely unknown to many.

Inquiry into the food habits of this bird covered 551 stomachs, collected in 29 States, the District of Columbia, and Canada, and representing every month of the year, though all the stomachs taken in winter were collected in the Southern States, the District of Columbia, and California. In the primary analysis the food was found to consist of 64.51 per cent of animal matter to 35.49 per cent of vegetable. The former is mostly composed of insects with some spiders, while the latter is largely fruit, chiefly wild species.

Animal food.– Beetles constitute 15.13 per cent of the food. Of these 2.98 per cent are of the useful family, Carabidæ. The remainder are mostly harmful. Scarabæidæ, the larvæ of which are the white grubs that destroy the roots of so many plants, were eaten to the extent of 3.44 per cent. Snout beetles, among the most harmful of insects, were taken to the extent of 3.13 per cent. Among these was the notorious plum curculio (Conotrachelus nenuphar) found in two stomachs taken in the District of Columbia in April of different years. Two other species of the same genus also were found, as well as the clover weevil (Epicærus imbricatus). The Colorado potato beetle (Leptinotarsa decemlineata) and the striped squash beetle (Diabrotica vittata), with a number of other species of less notoriety, were found in several stomachs. Thus, in spite of the bird's retiring habits, it comes in contact with some of the pests of cultivation.

The ants destroyed – 12.46 per cent of the food – keep up the reputation of thrushes as ant eaters. They were taken constantly every month, with the greatest number from May to September; a falling off in July is partly accounted for by the fact that more fruit is taken in that month. Other Hymenoptera (bees and wasps) were eaten to the extent of 5.41 per cent, a surprising amount for a bird that feeds so largely upon the ground, as these insects are usually of fleet wing and live in sunshine and open air.

Caterpillars, eaten in every month and mostly in goodly quantities, appear to be a favorite food of the hermit thrush. December is the month of least consumption (2.75 per cent), while the most were eaten in June (17.08 per cent). The average for the year is 9.54 per cent. Hemiptera (bugs) seem to be eaten whenever found, as they appear in the food of every month, but rather irregularly and not in large quantities. The greatest consumption was in June (9.17 per cent), but July, September, and December show the least (less than 1 per cent). The total for the year is 3.63 per cent. Of the six families represented, the Pentatomidæ, or stink bugs, predominate. These highly flavored insects are eaten by most insectivorous birds often, but usually in small quantities.

Diptera (flies) comprise 3.02 per cent of the food of the hermit thrush. The record shows, however, that nearly all of them are either crane flies (Tipulidæ) and their eggs and larvæ, or March flies (Bibio) and their larvæ. Over 150 of the latter were found in one stomach. Both of these families of flies lay their eggs in the ground, which accounts for their consumption by ground-feeding birds. Orthoptera (grasshoppers and crickets) are eaten by the hermit thrush to the extent of 6.32 per cent of its food. While this figure is not remarkable, it is the highest for any of the genus. These birds are fond of dark moist nooks among trees and bushes and do not feed extensively in those dry sunshiny places so much frequented by grasshoppers. A close inspection of the food record shows that the Orthoptera eaten by the thrushes are mostly crickets, which live in shadier and moister places than those where grasshoppers abound. A few miscellaneous insects (0.27 per cent) close the insect account. Spiders and myriapods (7.47 per cent) seem to constitute a very acceptable article of diet, as they amount to a considerable percentage in nearly every month, and in May rise to 20.79 per cent. A few miscellaneous animals, as sowbugs, snails, and angleworms, make up the balance of the animal food (1.26 per cent).

Following is a list of insects so far as identified and the number of stomachs in which found:

Vegetable food.– The vegetable diet of the hermit thrush consists largely of fruit, as with most birds of this group. As might be expected of a bird of such retiring habits, but little of the fruit eaten can be classed as cultivated. In September 5.45 per cent was so considered, but in most months the quantity was small, and in March, April, and May was completely wanting. The total for the year as found in 17 stomachs is 1.20 per cent. One stomach contained strawberries, one grapes, one figs, one currants, two apples, and the rest Rubus fruit, i. e., blackberries or raspberries. These last as well as the strawberries were probably wild. Of the wild fruit (26.19 per cent) 46 species were identified with a reasonable degree of certainty in 243 stomachs. A few seeds, ground-up vegetable matter not further identified, and rubbish make up the rest of the vegetable food (8.10 per cent). Among the seeds were some of the various species of poisonous Rhus. These were found in 18 stomachs, mostly from California. The dissemination of these seeds is unfortunate from the standpoint of husbandry, but many birds engage in it, as the waxy coating of the seeds is nutritious, especially in winter, when fruit and insects are not easily obtainable.

Following is a list of the components of the vegetable food so far as identified, and the number of stomachs in which found:

In looking over this list one is impressed with the fact that the taste of human beings for fruit differs markedly from that of birds. For example, Rhus seeds are hard and have little pulp to render them palatable or nutritious. They are usually passed through the alimentary canal of birds or regurgitated unharmed, and the slight outer coating alone is digested. In the case of the poisonous species, this outer coating is a white wax or tallow which appears to be very nutritious, for these species are eaten much more extensively than the nonpoisonous ones. The seed itself is rarely broken in the stomach to get any nutriment it may contain. But in spite of these facts Rhus seeds were found in 49 stomachs, while fruits of huckleberries and blueberries, which are delicious to the human taste, were found in only 13 stomachs; and blackberries and raspberries, highly esteemed by man, were found in only 5 stomachs. Next to Rhus the fruit most eaten was the dogwood berry, found in 34 stomachs, yet from a human estimate these berries are distasteful and contain such large seeds that they afford but very little actual food.

Summary.– The hermit thrush, as it name indicates, is of solitary habits and neither seeks human companionship nor molests cultivated products. It destroys nothing indirectly helpful to man, as beneficial insects, but aids in the destruction of the myriad hosts of insect life which at all times threaten vegetation. While it is not easy to point out any especially useful function of the hermit thrush, it fills its place in the economy of nature, from which it should not be removed.