Food Habits of the Thrushes of the United States Part 1

Food Habits of the Thrushes of the United States.

by F. E. L. Beal.

INTRODUCTION.

North American thrushes (t.u.r.didae) const.i.tute 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 (_t.u.r.dus musicus_) is accidental in Greenland, and the wheatears (_Saxicola nanthe_ 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 aliciae_ 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 setae 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 ca.n.a.ls mixed with the hard indigestible setae or spines.

Thrushes of the genus _Hylocichla_ show a very p.r.o.nounced taste for ants, and the average consumption of these insects by the five species is 12.65 per cent. Few birds other than woodp.e.c.k.e.rs 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 (gra.s.shoppers), which are a favorite food with most birds, do not seem to appeal much to the thrushes.

The thrushes are p.r.o.nounced 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 const.i.tutes 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 p.r.o.nounced "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 rus.h.i.+ng 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 const.i.tute the second largest item (10.74 per cent), but 5.89 per cent of these were the useful predatory ground beetles (Carabidae). 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 Carabidae--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 const.i.tuted the usual diet of the species they would have appeared in other months and in more stomachs, but in smaller quant.i.ties. Other families of beetles are eaten so sparingly as to be of little importance.

Scarabaeidae 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, const.i.tuted the whole contents. Gra.s.shoppers 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:

COLEOPTERA.

_Amara erratica_ 1 _Aphodius_ sp 1 _Balaninus_ sp 1

HEMIPTERA.

_Platypedia putnami_ 1

_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 cla.s.sified 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 quant.i.ty 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 ma.s.s 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:

Rocky Mountain cedar (_Juniperus scopulorum_) 3 Western cedar (_Juniperus monospermum_) 1 Other cedars (_Juniperus_ sp.) 2 Hackberries (_Celtis occidentalis_) 1 Douglas hackberries (_Celtis douglasii_) 1 Service berries (_Amelanchier_ sp.) 1 Rose haws (_Rosa_ sp.) 2 Wild cherries (_Prunus_ sp.) 1 Sumac berries (_Rhus_ sp.) 1 Poison ivy (_Rhus toxicodendron_) 1 Waxwork (_Celastrus_ sp.) 1 Madrona berries (_Arbutus menziesii_) 5 Honeysuckle berries (_Lonicera_ sp.) 1 Elderberries (_Sambucus_ sp.) 1 Fruit not further identified 3

_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 pa.s.s 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 quant.i.ty 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), const.i.tute the largest item of animal food. Of these, 2.23 per cent are the predacious ground beetles (Carabidae), generally considered useful. The remainder belong to several more or less harmful families, of which the May-beetle family (Scarabaeidae) 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 (Elateridae) 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 gra.s.s. The well-known white grubs that attack gra.s.s 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.

[Ill.u.s.tration: B2084-73

Fig. 1.--Wood thrush (_Hylocichla mustelina_).]

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 quant.i.ties. Diptera (flies) are eaten in small quant.i.ties and rather irregularly. Most of them were the long-legged crane flies (Tipulidae), 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 (gra.s.shoppers) are eaten in small quant.i.ties 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, const.i.tuting in April 20.94 per cent of the food, but gradually decreasing in quant.i.ty 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:

HYMENOPTERA.

_Tiphia inornata_ 1

COLEOPTERA.

_Harpalus herbivagus_ 1 _Necrophorus tomentosus_ 1 _Philonthus lomatus_ 1 _Hister abbreviatus_ 1 _Hister depurator_ 1 _Hister america.n.u.s_ 2 _Ips quadriguttatus_ 1 _Melanotus america.n.u.s_ 1 _Corymbites cylindriformis_ 1 _Agrilus bilineatus_ 1 _Telephorus carolinus_ 1 _Onthophagus striatulus_ 1 _Onthophagus tuberculifrons_ 1 _Onthophagus_ sp 3 _Ataenius_ sp 2 _Aphodius granarius_ 1 _Aphodius_ sp 1 _Dichelonycha testacea_ 1 _Dichelonycha_ sp 1 _Lachnosterna_ sp 27 _Ligyrus_ sp 1 _Allorhina nitida_ 1 _Euphoria fulgida_ 1 _Euphoria_ sp 2 _Chrysomela pulchra_ 1 _Leptinotarsa decemlineata_ 2 _Odontota_ sp 1 _Coptocycla signifera_ 1 _Coptocycla_ sp 1 _Anametus griseus_ 1 _Phyxelis rigidus_ 1 _Otiorhynchus ovatus_ 2 _Tanymecus confertus_ 1 _Pandeletejus hilaris_ 1 _Barypithes pellucidus_ 1 _Listronotus latiusculus_ 1 _Macrops_ sp 1 _Conotrachelus posticatus_ 2 _Acalles carinatus_ 1 _Balaninus_ sp 2 _Eupsalis minuta_ 1 _Sphenophorus parvulus_ 1

HEMIPTERA.

_Nezara hilaris_ 2