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.
| White cedar seeds (Thuja occidentalis)1 Red cedar berries (Juniperus communis)2 False Solomon's seal (Smilacina trifolia)3 Greenbrier (Smilax tamnifolia)1 Cat brier (Smilax sp.)1 Hackberry (Celtis occidentalis)3 Mulberry (Morus sp.)2 Fig (Ficus sp.)3 Pale persicaria (Polygonum lapathifolium)1 Poke berries (Phytolacca decandra)9 Mountain ash (Pyrus americana)1 Service berries (Amelanchier sp.)1 Blackberries or raspberries (Rubus sp.)67 Rose haws (Rosa sp.)1 Wild black cherries (Prunus serotina)15 Bird cherries (Prunus Pennsylvanica)2 Domestic cherries (Prunus cerasus)29 Domestic plum (Prunus domestica)2 Apricot (Prunus armeniaca)3 Filaree (Erodium sp.)1 Poison oak (Rhus diversiloba)4 Staghorn sumac (Rhus hirta)2 Dwarf sumac (Rhus copallina)3 Other sumac (Rhus sp.)4 Pepper tree (Schinus molle)1 American holly (Ilex opaca)1 | Black alder (Ilex verticillata)1 Coffee berries (Rhamnus californicus)3 Woodbine (Psedera quinquefolia)10 Frost grape (Vitis cordifolia)6 Spikenard (Aralia racemosa)2 Flowering dogwood (Cornus florida)7 Kinnikinnik (Cornus amomum)2 Red osier (Cornus stolonifera)1 Panicled cornel (Cornus paniculata)3 Dogwood unidentified (Cornus sp.)6 Huckleberries (Gaylussacia sp.)1 Three-flowered nightshade (Solanum triflorum)1 Nightshade unidentified (Solanum sp.)8 Black twinberries (Lonicera involucrata)2 Honeysuckle berries (Lonicera sp.)2 Snowberries (Symphoricarpos racemosus)2 Dockmackie (Viburnum acerifolium)1 Arrowwood (Viburnum sp.)1 Black elderberries (Sambucus canadensis)6 Red elderberries (Sambucus pubens)5 Blue elderberries (Sambucus glauca)15 Tarweed (Madia sp.)1 Fruit pulp not further identified17 |
| White cedar seeds (Thuja occidentalis) | 1 |
| Red cedar berries (Juniperus communis) | 2 |
| False Solomon's seal (Smilacina trifolia) | 3 |
| Greenbrier (Smilax tamnifolia) | 1 |
| Cat brier (Smilax sp.) | 1 |
| Hackberry (Celtis occidentalis) | 3 |
| Mulberry (Morus sp.) | 2 |
| Fig (Ficus sp.) | 3 |
| Pale persicaria (Polygonum lapathifolium) | 1 |
| Poke berries (Phytolacca decandra) | 9 |
| Mountain ash (Pyrus americana) | 1 |
| Service berries (Amelanchier sp.) | 1 |
| Blackberries or raspberries (Rubus sp.) | 67 |
| Rose haws (Rosa sp.) | 1 |
| Wild black cherries (Prunus serotina) | 15 |
| Bird cherries (Prunus Pennsylvanica) | 2 |
| Domestic cherries (Prunus cerasus) | 29 |
| Domestic plum (Prunus domestica) | 2 |
| Apricot (Prunus armeniaca) | 3 |
| Filaree (Erodium sp.) | 1 |
| Poison oak (Rhus diversiloba) | 4 |
| Staghorn sumac (Rhus hirta) | 2 |
| Dwarf sumac (Rhus copallina) | 3 |
| Other sumac (Rhus sp.) | 4 |
| Pepper tree (Schinus molle) | 1 |
| American holly (Ilex opaca) | 1 |
| Black alder (Ilex verticillata) | 1 |
| Coffee berries (Rhamnus californicus) | 3 |
| Woodbine (Psedera quinquefolia) | 10 |
| Frost grape (Vitis cordifolia) | 6 |
| Spikenard (Aralia racemosa) | 2 |
| Flowering dogwood (Cornus florida) | 7 |
| Kinnikinnik (Cornus amomum) | 2 |
| Red osier (Cornus stolonifera) | 1 |
| Panicled cornel (Cornus paniculata) | 3 |
| Dogwood unidentified (Cornus sp.) | 6 |
| Huckleberries (Gaylussacia sp.) | 1 |
| Three-flowered nightshade (Solanum triflorum) | 1 |
| Nightshade unidentified (Solanum sp.) | 8 |
| Black twinberries (Lonicera involucrata) | 2 |
| Honeysuckle berries (Lonicera sp.) | 2 |
| Snowberries (Symphoricarpos racemosus) | 2 |
| Dockmackie (Viburnum acerifolium) | 1 |
| Arrowwood (Viburnum sp.) | 1 |
| Black elderberries (Sambucus canadensis) | 6 |
| Red elderberries (Sambucus pubens) | 5 |
| Blue elderberries (Sambucus glauca) | 15 |
| Tarweed (Madia sp.) | 1 |
| Fruit pulp not further identified | 17 |
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.