Food Habits of the Thrushes of the United States

Food Habits of the Thrushes of the United States
Foster Beal

Food Habits of the Thrushes of the United States / USDA Bulletin 280

INTRODUCTION

North American thrushes (Turdidæ) constitute a small but interesting group of birds, most of which are of retiring habits but noted as songsters. They consist of the birds commonly known as thrushes, robins, bluebirds, Townsend's solitaire, and the wheatears. The red-winged thrush of Europe (Turdus musicus) is accidental in Greenland, and the wheatears (Saxicola œnanthe subspp.) are rarely found in the Western Hemisphere except in Arctic America. Within the limits of the United States are 11 species of thrushes, of which the following 6 are discussed in this bulletin: Townsend's solitaire (Myadestes townsendi), the wood thrush (Hylocichla mustelina), the veery and willow thrush (Hylocichla fuscescens subspp.), the gray-cheeked and Bicknell's thrushes (Hylocichla aliciæ subspp.), the olive-backed and russet-backed thrushes (Hylocichla ustulata subspp.), and the hermit thrushes (Hylocichla guttata subspp.). An account of the food habits of the 5 species of robins and bluebirds appeared in Department Bulletin No. 171.

As a group thrushes are plainly colored and seem to be especially adapted to thickly settled rural districts, as the shyest of them, with the exception of the solitaire, do not require any greater seclusion than that afforded by an acre or two of woodland or swamp.

The thrushes are largely insectivorous, and also are fond of spiders, myriapods, sowbugs, snails, and angleworms. The vegetable portion of their diet consists mostly of berries and other small fruits. As a family thrushes can not be called clean feeders, for the food eaten often contains a considerable proportion of such matter as dead leaves, stems, and other parts of more or less decayed vegetation. It might be supposed that this was gathered from the ground with insects and other food, but investigation shows that much of it has a different origin. It was noticed that the setæ or spines of earthworms were a very common accompaniment of this decayed vegetation. Earthworms themselves are rather rarely found in stomachs, although some birds, as the robin, eat them freely. It is well known that the food of earthworms consists largely of partially decayed vegetable matter found in the soil. Hence it is probable that decayed vegetation found in the stomachs of thrushes is the food contained in the earthworms when they were swallowed. The tissues of worms are quickly digested, leaving the contents of their alimentary canals mixed with the hard indigestible setæ or spines.

Thrushes of the genus Hylocichla show a very pronounced taste for ants, and the average consumption of these insects by the five species is 12.65 per cent. Few birds other than woodpeckers show so strong a liking for this highly flavored food. Hymenoptera in general, including ants, bees, and wasps, are the second largest item of insect food. Lepidoptera (caterpillars) stand next as an article of thrush diet, while Orthoptera (grasshoppers), which are a favorite food with most birds, do not seem to appeal much to the thrushes.

The thrushes are pronounced ground feeders, and may often be seen picking small fruit that has fallen to the ground. The vegetable portion of their food (40.72 per cent) is largely composed of fruit, which constitutes over 34 per cent of the total food. Of this 30.88 per cent is made up of wild berries, which outweigh the domestic varieties with every species. In all, 94 species of wild fruits or berries were identified in the stomachs of these birds, although it is not always practicable to identify such material unless seeds or some other characteristic parts are present. As this is not often the case, a considerable portion of the stomach contents must be pronounced "fruit pulp" without further identification; thus probably many more species are eaten than are recorded. Moreover, in the case of some fruits, it is not possible to distinguish species by the seeds, so that many species go unrecognized except as to genus. Domestic fruits are eaten so sparingly by the thrushes here considered as to be of no economic importance.

Note. – This bulletin treats of the economic relations and value to agriculture of the thrushes of the United States other than robins and bluebirds. These two forms were discussed in Department Bulletin No. 171, issued February 5, 1915.

TOWNSEND'S SOLITAIRE

(Myadestes townsendi.)

Townsend's solitaire, a bird of the far West, is a resident of high mountains and lonely gorges. It is partial to running streams and often builds its nest just above a rushing mountain torrent. It ranges from Alaska through the Sierras south to San Bernardino, Cal., and through the Rockies to Arizona and New Mexico, and occasionally farther east. The species is not evenly distributed over this region, but is restricted to such high mountainous portions as afford its favorite surroundings. As long as it retains these habits the bird will have little or no effect upon the products of husbandry, and its food can have only a scientific interest. The song of this species is said to be at times the finest of any of the thrush family.

As this bird is comparatively rare in settled regions only 41 stomachs are available for determining the character of its food. The most southerly and easterly one was taken in Texas, the most westerly in California, and the most northerly in Wyoming. They are distributed through all the months of the year, although April and May are represented by but one each and December by but two. Every other month has three or more. An investigation based upon such limited material can be considered only as preliminary, but will serve to show some of the more important elements of the food. This was made up of 35.90 per cent of animal matter to 64.10 of vegetable.

Animal food.– The animal food consists of insects and spiders, with a few hair worms (Gordius) found in one stomach. These last may have been contained in the insects eaten. Among insects, beetles constitute the second largest item (10.74 per cent), but 5.89 per cent of these were the useful predatory ground beetles (Carabidæ). This is not a good showing, but too few stomachs have been examined to allow sweeping conclusions. As evidence that this can not be taken as a fair sample of the bird's food habits it may be stated that all of these beetles were taken in January and October. The one stomach collected in January contained 95 per cent of Carabidæ – the only animal food in it – and 93 per cent of the contents of one October stomach was made up of the same material. Evidently in these cases the bird had found a colony of the beetles and filled up with them. Had they constituted the usual diet of the species they would have appeared in other months and in more stomachs, but in smaller quantities. Other families of beetles are eaten so sparingly as to be of little importance. Scarabæidæ stand the next highest, but they amount to less than 2 per cent of the food.

Lepidoptera (caterpillars) make the largest item in the food of Myadestes. Eaten much more regularly than beetles, they probably are a standard article of diet. They were found in the stomachs collected in every month of the year but four, and a greater number of stomachs would probably show them in every month. The one stomach taken in May contained the maximum (72 per cent). The total for the year is 12.95 per cent. Ants are eaten to the extent of 4.71 per cent, while other Hymenoptera, as bees and wasps, make up less than half of 1 per cent. Diptera (flies) are represented by a mere trace in the stomachs. Observers who have seen this bird in its native haunts testify that it takes a considerable portion of its food on the wing. In view of this fact it seems curious that the two orders of insects most active on the wing (Hymenoptera and Diptera) should be so scantily represented in the food. Hymenoptera are a standard diet with flycatchers and would seem to be the natural food of any bird that feeds upon the wing.

Hemiptera (bugs) were found to the extent of 3.51 per cent of the total food. All were contained in three stomachs taken in March, June, and July. In the July stomach four cicadas, or dog-day flies, constituted the whole contents. Grasshoppers amount to less than 1 per cent and all other insects to but a trifle. Spiders were eaten to the extent of 2.94 per cent of the food and were found in the stomachs taken in seven of the twelve months, and judging from their distribution they are eaten whenever available. A hair snake (Gordius) was found in one stomach. Following is a list of insects identified and the number of stomachs in which found:

Vegetable food.– The vegetable portion of the food of Myadestes is 64.10 per cent of the whole, and 58.70 per cent of this, or more than half the whole food, is classified as wild fruit or berries. These were found in stomachs collected in every month. From the even distribution of this food through the year and from the quantity eaten it is evidently a favorite article of diet. Nothing was found in any of the stomachs that could be identified as cultivated fruit, with the possible exception of a mass of fruit pulp found in one. A few seeds of poison ivy and sumac, with fragments of flowers and a few weed seeds, complete the vegetable food. Following is a list of fruits, seeds, etc., identified, and the number of stomachs in which found:

Summary.– With so small an amount of material it is not safe to draw general conclusions, but in the case of Myadestes one point seems clear – the bird's favorite food is small wild fruit, and as long as this is abundant the bird will probably not attack cultivated varieties; but should any portion of the region occupied by the solitaire be cleared of its wild fruit and cultivated species be introduced these would likely be preyed upon. Under such conditions this bird, now perfectly harmless, might inflict considerable damage.

WOOD THRUSH

(Hylocichla mustelina.)

The wood thrush is distributed over the eastern part of the United States wherever suitable conditions are found. It is a lover of open groves and bushy pastures, and may be found along little-traveled roads and near low bushy swamps. The bird is noted for its sweet song, and many country people who are well acquainted with its notes know little or nothing of the bird itself. Its favorite time for singing is in the early evening at the close of a sultry afternoon when a shower has cooled the air. As a rule, it does not nest in gardens or orchards and is seldom seen about farm buildings. It is strictly migratory, and the greater number pass out of the United States in winter, though a few remain in the Southern States. It usually migrates north in April or early May.

For the investigation of the food habits of the wood thrush 171 stomachs were available. One of these was collected in Florida in January and another in Alabama in February, and these two will be treated separately. The remaining 169 were collected from April to October, and are fairly well distributed over that time. The food consisted of 59.59 per cent of animal matter to 40.41 per cent of vegetable. The greatest quantity of animal food was eaten in April, the month of arrival from the south, and the least in October, the month of the return migration.

Animal food.– Beetles, collectively (20.40 per cent), constitute the largest item of animal food. Of these, 2.23 per cent are the predacious ground beetles (Carabidæ), generally considered useful. The remainder belong to several more or less harmful families, of which the May-beetle family (Scarabæidæ) amount to 10.17 per cent. Snout beetles, or weevils (Rhynchophora), are eaten to the extent of 2.16 per cent only, and the wood-boring chick-beetles (Elateridæ) to 2.13 per cent.

Among the various species of these insects were noted the remains of the well-known Colorado potato beetle (Leptinotarsa decemlineata), in two stomachs, and Coptocycla signifera, also injurious to the potato, in one stomach. Remains of Otiorhynchus ovatus, a weevil destructive to strawberry plants, were found in two stomachs, and in one other a weevil, Sphenophorus parvulus, that injures the roots of grass. The well-known white grubs that attack grass roots and a host of other plants are the immature forms of many species of Lachnosterna, of several species of Euphoria and of Allorhina nitida. Of these, remains of Lachnosterna were found in 27 stomachs and of Allorhina and Euphoria in one each.

Lepidoptera (caterpillars) stand next to Coleoptera (beetles) in the animal diet of the wood thrush. Although eaten with a fair degree of regularity during every month of the bird's stay in the north, the most were taken in July (16.32 per cent). The average for the season is 9.42 per cent. Ants as an item of food are third in importance, though if other Hymenoptera were included the order would rank next to beetles. They seem to be a rather favorite food with all birds of the genus Hylocichla. With the wood thrush they begin with 18.12 per cent in April and gradually decrease through the summer and disappear in October. The total for the season is 8.89 per cent. Hymenoptera other than ants were eaten with great regularity (3.86 per cent) throughout the season, but not in large quantities. Diptera (flies) are eaten in small quantities and rather irregularly. Most of them were the long-legged crane flies (Tipulidæ), both in the adult and larval form. The total for the season is 2.70 per cent. Hemiptera (bugs) do not appear to be a favorite food, though a few were taken in all of the seven months except October. The average for the season is only 1.33 per cent. Orthoptera (grasshoppers) are eaten in small quantities until July, after which they form a fair percentage till September. The total consumption amounts to 2.28 per cent of the food. A few other insects make up a fraction of 1 per cent. Spiders and myriapods (thousand-legs) appear to be a favorite food with the wood thrush, constituting in April 20.94 per cent of the food, but gradually decreasing in quantity until September. The aggregate for the year is 8.49 per cent. A few sowbugs (isopods), snails, and earthworms (1.83 per cent) close the account of animal food.

Following is a list of the insects identified in the stomachs of the wood thrush and the number of stomachs in which each was found:

Vegetable food.– More than nine-tenths of the vegetable food of the wood thrush can be included in a single item – fruit. Cultivated fruit, or what was thought to be such, was found in stomachs taken from June to September, inclusive. It was eaten regularly and moderately, and the total for the season was 3.74 per cent of the whole food. Wild fruits or berries of 22 species were found in 72 stomachs, distributed through every month of the bird's stay at the north. Beginning with 1.18 per cent in April, the quantity gradually increases to 87.17 per cent in October, when it makes more than five-sixths of the whole food. The average for the season is 33.51 per cent. In this investigation Rubus seeds (blackberries or raspberries) are always reckoned as cultivated fruit, though probably most often wild. Besides fruit, a few seeds and rose haws were found, which with a little rubbish complete the vegetable food (40.41 per cent).

Following is a list of fruits, seeds, etc., identified and the number of stomachs in which found:

Of the two stomachs not included in the foregoing discussion, the one taken in Florida in January contained 93 per cent of wild fruit and 7 per cent of weevils, wasps, and spiders; the one collected in Alabama in February was entirely filled with animal food, of which 88 per cent was caterpillars, 5 per cent May beetles, 6 per cent bugs, and 1 per cent spiders.

Summary.– The animal food of the wood thrush includes remarkably few useful insects and contains some very harmful ones, as the Colorado potato beetle and many of the Scarabæidæ, the larval forms of which are the well-known white grubs which are a pest to agriculture in preying upon roots of plants. The vegetable portion of the food contains a small quantity of cultivated fruit, but observation shows that the thrush is in the habit of picking up fallen fruit instead of taking it fresh from the tree. The eating of wild fruit has no economic interest except that it serves to distribute the seeds of many shrubs and trees. There is no occasion to discriminate against this bird in any way. It should be rigidly protected.

VEERY AND WILLOW THRUSH

(Hylocichla fuscescens fuscescens and Hylocichla fuscescens salicicola.)

The veery is distributed over the eastern portion of the United States during migration and breeds in the Northern States as far south as Pennsylvania, and in New England and Canada. In winter it disappears almost entirely from the country, only a few remaining in Florida and perhaps in other Southern States. Its western representative is the willow thrush. Like other thrushes, birds of this species are shy and retiring in disposition, keeping for the most part in the shade of woods or bushy swamps, or building nests in a damp ravine with a brook gurgling past. They have been known, however, to visit orchards and sometimes gardens which are not kept too trim. It is thus evident that the food has little direct economic interest, as this bird does not come in contact with the farmer's crops.

For investigating the food of the species 176 stomachs were available. They were collected during the seven months from April to October, and represent 18 States, the District of Columbia, and Canada. The food separates into 57.27 per cent of animal matter and 42.73 per cent of vegetable. The former consists mostly of remains of insects, and the latter of fruit.

Animal food.– Predacious ground beetles (Carabidæ) amount to 0.82 per cent. They are evidently not a preferred food. Beetles in general comprise 14.67 per cent of the food, but no family or other group appears to be distinguished except the Carabidæ, which are conspicuous by their absence. Weevils, or snout beetles, amount to 2.49 per cent, and one stomach contained a specimen of the notorious plum curculio (Conotrachelus nenuphar). A number of other harmful beetles were noted, but none are so well known as the plum destroyer. Ants make up 10.35 per cent and are eaten with great regularity. Hymenoptera other than ants amount to only 3.26 per cent, but are eaten regularly throughout the season. Hemiptera (bugs) were eaten to a small extent (1.30 per cent) in the first four months, but they are not seen after July. Exactly the same may be said of Diptera, which total only 0.85 per cent.

Lepidoptera (caterpillars) are, next to Hymenoptera, the favorite insect food. They were eaten in goodly quantities in every month except October. The average for the season is 11.91 per cent. Grasshoppers appear to some extent in every month except April, the greatest consumption taking place in October (24 per cent), but as only small numbers are eaten in the earlier months the aggregate for the year is only 4.91 per cent. A few other insects of various orders amount to 0.98 per cent. Spiders (6.34 per cent) are eaten regularly and constantly through the season, except that none were taken in October. A few sowbugs, snails, etc. (2.70 per cent), complete the quota of animal food. Following is a list of insects identified and the number of stomachs in which found:

Vegetable food.– The vegetable portion of the food of the species is made up of fruit, with a few seeds and a little miscellaneous matter more or less accidental. Fruit collectively amounts to 35.30 per cent, of which 12.14 per cent was thought to be of cultivated varieties and so recorded, while the remainder, 23.16 per cent, was quite certainly of wild species. This percentage of cultivated fruit is more than three times the record of the wood thrush, while the wild fruit eaten is correspondingly less, as the sum total of the fruit consumed is very nearly the same with both birds. From this percentage of domestic fruit one might infer that the veery was, or might be, a serious menace to fruit growing, but no such complaints have been heard, and it is probable that the species is not numerous enough to damage cultivated crops. A close inspection, however, of the fruit eating of the veery removes all doubts. The cultivated fruit, so called, was in every case either strawberries or Rubus fruits, i. e., blackberries or raspberries, and as both of these grow wild and in abundance wherever the veery spends its summer, it is probable that all of the fruit eaten was taken from wild plants, though 12.14 per cent has been conventionally recorded as cultivated.

Besides fruit, the veery eats a few seeds of grasses and weeds and a few of sumac, but none of the poisonous species were found in the stomachs. These seeds (7.25 per cent of the food) were eaten so irregularly as to suggest that they are merely a makeshift taken for want of something better. Rubbish (0.18 per cent), consisting of decayed wood, bits of leaves, plant stems, etc., completes the vegetable food.

Following is a list of the items of vegetable food and the number of stomachs in which found:

Summary.– It is hardly necessary to make a summary of the food of this bird in order to bring out its good points, for it seems to have no others. The animal food includes less than 1 per cent of useful beetles, and the remainder is either harmful or neutral. In the matter of vegetable food there seems to be no chance for criticism, as nature evidently supplies all it needs. The bird has never been harmed, but has been held in high esteem for sentimental reasons; let it also be valued and protected for its economic worth.

GRAY-CHEEKED AND BICKNELL'S THRUSHES

(Hylocichla aliciæ aliciæ and Hylocichla aliciæ bicknelli.)

The gray-cheeked thrush (H. a. aliciæ) is found in migration over all the Eastern States, but breeds farther north, beyond our limits. Bicknell's thrush (H. a. bicknelli), a closely related form, while having somewhat the same general range, breeds farther south and nests in the mountains of northern New York and New England. Both subspecies have the same general habits as other forms of the genus so far as haunts and choice of residence are concerned, but their far-northern range excludes them from coming into contact with cultivated crops. The species does not seem to be very abundant anywhere, and consequently only a few stomachs have been received for examination. In all they number but 111 and are very irregularly distributed in time. None were taken in August and only one in July and two in June. From so scanty and unevenly distributed material it is impossible to draw final conclusions, but we can get some idea as to the nature of the bird's food and its economic importance.

The first analysis of the food gives 74.86 per cent of animal matter to 25.14 per cent of vegetable. This is the most animal food found in the stomachs of any bird of the genus Hylocichla and the largest but two of any of the thrushes.

Animal food.– Beetles collectively amount to about one-third of all the food (33.32 per cent). Of these, 2.83 per cent are the useful Carabidæ. The rest belong to harmful families, such as the Scarabæidæ, Elateridæ, and the weevils, or snout beetles. Ants amount to 16.34 per cent and are eaten very regularly – the most in the early part of the season. Hymenoptera other than ants, as wasps and bees, were eaten to the extent of 5.60 per cent, and with the ants make 21.94 per cent, placing this food next in rank to beetles. As in the case of ants, most of the bees and wasps were eaten in the first three months of the season. No honey bees were found. Lepidoptera (caterpillars) were third in order of abundance (8.81 per cent). No special pest was discovered, but all caterpillars may be considered as harmful. A few grasshoppers were found in the stomachs taken in April and May, and more in those collected in September and October. They do not appear to be a favorite food and amount to only 1.72 per cent. Other insects, as flies, bugs, and a few others, collectively amount to 2.89 per cent. Among these, it is of interest to note in one stomach the remains of the famous seventeen-year locust (Tibicen septemdecem), rather large game for so small a bird. Spiders are freely eaten by the gray-cheeked thrush in spring, and sparingly in fall. For the season they constitute 5.77 per cent of the food. A few other animals, as crawfish, sowbugs, and angleworms (0.41 per cent), complete the animal food.

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

Vegetable food.– A few Rubus seeds were recorded as cultivated fruit, but they were found in only two stomachs and probably were wild, as the gray-cheeked thrush does not live where it is likely to come in contact with cultivated blackberries or raspberries. In any case they amount to only 0.15 per cent. Wild fruits of 18 different species (23.98 per cent) make up nearly one-fourth of the whole food – in fact, the vegetable food, other than wild fruit, is insignificant. Wild berries supplement the regular food, which consists of insects and spiders.

The following list shows the fruits and seeds identified and the number of stomachs in which found:

Summary.– In the food of the gray-cheeked thrush the only useful element is a small percentage (2.83) of useful beetles. The remainder of the animal food is composed of either harmful or neutral elements. The vegetable food, drawn entirely from nature's great storehouse, contains no product of human industry, either of grain or fruit. Whatever the sentimental reasons for protecting this bird, the economic ones are equally valid.

OLIVE-BACKED AND RUSSET-BACKED THRUSHES