The government dissected 855 bluebird stomachs to settle what the bird actually eats through the year — every figure and every berry on this page is reprinted word for word from that bulletin, the Forest Service’s species accounts, and a naturalist’s account of the nestlings, cited at the end.
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Check PriceThe verdict from 855 stomachs
The eastern bluebird (fig. 1), one of the most familiar and welcome of our feathered visitors, is a common inhabitant of all the States east of the Rocky Mountains from the Gulf of Mexico to southern Canada. In the Mississippi valley it winters as far north as southern Illinois, and in the East as far as Pennsylvania.
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It is one of the earliest northern migrants, and everywhere is hailed as a harbinger of spring. Very domestic in habits, it frequents orchards and gardens, and builds its nests in cavities of trees, crannies in farm buildings, or boxes provided for its use.
The bluebird has not been accused, so far as known, of stealing fruit or of preying upon crops. An examination of 855 stomachs showed that 68 per cent of the food consists of insects and their allies, while the other 32 per cent is made up of various vegetable substances, found mostly in stomachs taken in winter.
Beetles constitute 21 per cent of the whole food, grasshoppers 22, caterpillars 10, and various other insects 9, while a number of spiders and myriapods, about 6 per cent, comprise the remainder of the animal diet. All these are more or less harmful, except a few predacious beetles, which amount to 9 per cent. In view of the large consumption of grasshoppers and caterpillars, we may at least condone this offense, if such it may be called.
The destruction of grasshoppers is very noticeable in August and September, when these insects make up about 53 per cent of the diet.
It is evident that in the selection of its food the bluebird is governed more by abundance than by choice. Predacious beetles are eaten in spring, as they are among the first insects to appear; but in early summer caterpillars form an important part of the diet, and these are later replaced by grasshoppers. Beetles are eaten at all times, except when grasshoppers are more easily obtained.
So far as its vegetable food is concerned the bluebird is positively harmless. The only trace of any useful product in the stomachs consisted of a few blackberry seeds, and even these probably belonged to wild rather than cultivated varieties. Following is a list of the various seeds which were found; Blackberry, chokeberry, juniperberry, pokeberry, partridgeberry, greenbrier, Virginia creeper, bittersweet, holly, strawberry bush, false spikenard, wild sarsaparilla, sumac (several species), rose haws, sorrel, ragweed, grass, and asparagus.
This list shows how little the bluebird depends upon the farm or garden to supply its needs and how easily, by encouraging the growth of some of these plants, many of which are highly ornamental, the bird may be induced to make its home on the premises.
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Two species of bluebirds inhabit the Western States—the mountain bluebird and the western bluebird. In their food habits they are even more to be commended than their eastern relative. Their insect food is obtainable at all times of the year, and the general diet varies only in the fall, when some fruit, principally elderberries, is eaten, though an occasional blackberry or grape is also relished.
In an examination of 217 stomachs of the western bluebird, animal matter (insects and spiders) was found to the extent of 82 per cent and vegetable matter to the extent of 18 per cent. The bulk of the former consists of bugs, grasshoppers, and caterpillars. Grasshoppers, when they can be obtained, are eaten freely during the whole season.
Caterpillars also are a favorite food and are eaten during every month of the year; March is the month of greatest consumption, with 50 per cent, and the average for the year is 20 per cent. Two stomachs taken in January contained 64 and 50 per cent, respectively, of caterpillars. Beetles also are eaten and comprise mostly harmful species.
The vegetable matter consists of weed seeds and small fruits. In December a few grapes are eaten, but elderberries are the favorites whenever they can be found. It is only when these are in their greatest abundance that vegetable exceeds animal food.
The Forest Service’s tally, species by species
Eastern bluebird. — Eastern bluebirds consume 70 percent animal matter and 30 percent vegetable matter. Vegetable intake increases to more than 50 percent in December and January, but is completely lacking in May. Animal matter includes grasshoppers, crickets and katydids, various coleoptera, moths and caterpillars, some hymenoptera and hemiptera, as well as various other invertebrates and small vertebrates. Vegetable matter is mostly wild fruits (Bent 1949).
Western bluebird. — Beal (Bent 1949) examined the contents of 217 stomachs and found 72 percent animal material (grasshoppers 21 percent, caterpillars 20 percent, useful beetles 9 percent, other beetles 16 percent, ants 5 percent, other hymenoptera 1 percent) and 28 percent vegetable material, mostly wild fruits, including elderberries, mistletoe berries, blackberries or raspberries, prunes, cherries, and a few weed seeds.
Mountain bluebird. — This is probably the most insectivorous of the bluebirds. Studies indicate that nearly 92 percent of the diet is animal material, including miscellaneous beetles, weevils, ants, bees, wasps, cicadas, stinkbugs, negro bugs, assassin bugs, jassids, flies, caterpillars, grasshoppers, locusts, and crickets (Bent 1949). Vegetable items include currants, grapes, elderberries, sumac seeds, mistletoe berries, hackberry seeds, Virginia creeper seeds, and cedar berries.
What the nestlings are fed
As no dampness is to be dried, laying follows closely upon the completion of the nest, and continues for a period of five days, one egg being laid daily. They are usually of a sky-blue color, spotless, and have an actual measurement of .82 by .61 inches. Mr. Ingersoll once found in Loraine County, Ohio, a nest of five eggs, all of which were pure lustrous white, like those of a Woodpecker.
Similar instances have come to our knowledge since the above was recorded. In the work of incubation, the male occasionally relieves his partner, but when not thus engaged, he is very attentive, and often cheers the monotony of her task by a soft, agreeable warble.
When hatched, the young are watched over with the greatest care, and fed alternately by each parent. Their food consists of flies, earthworms, young of beetles, moths, butterflies, etc. When able to shift for themselves, they are entrusted to the care of the male, while the female busies herself in preparing for the second brood.
The old nest is renovated and refurnished, and she again sits, depending upon her affectionate and trustful mate for the support of both herself and the brood which, as it sometimes happens, are not fairly out of the way when the second family of young are ushered into existence. As many as three broods are occasionally raised, when the season has been long and favorable.
The bluebird year, at a glance
| Season | What the sources say | The number |
|---|---|---|
| Spring | “Predacious beetles are eaten in spring, as they are among the first insects to appear”; western caterpillar consumption peaks in March | predacious beetles 9% of the whole food; March caterpillars 50% (western) |
| Early summer | “caterpillars form an important part of the diet”; nestlings fed flies, earthworms, young of beetles, moths, butterflies | caterpillars 10% of the whole food (year-round) |
| August–September | “The destruction of grasshoppers is very noticeable… when these insects make up about 53 per cent of the diet” | grasshoppers 53% |
| Fall | western species take “some fruit, principally elderberries… an occasional blackberry or grape” | — |
| December–January | “Vegetable intake increases to more than 50 percent”; “In December a few grapes are eaten, but elderberries are the favorites” | vegetable >50% |
| May | vegetable food “is completely lacking in May” — all insects | vegetable 0% |
| Who counted | Sample | Animal : vegetable |
|---|---|---|
| Farmers’ Bulletin 630 — eastern bluebird | 855 stomachs | 68 : 32 |
| Handbook 511 (citing Bent 1949) — eastern bluebird | — | 70 : 30 |
| Farmers’ Bulletin 630 — western bluebird | 217 stomachs | 82 : 18 |
| Handbook 511 (citing Beal via Bent) — western bluebird | 217 stomachs | 72 : 28 |
| Handbook 511 — mountain bluebird | — | ~92 : 8 |
Source
F. E. L. Beal, Some Common Birds Useful to the Farmer, USDA Farmers’ Bulletin 630, revised edition (1926), “The Bluebirds.” Scott, Evans, Patton & Stone, Cavity-Nesting Birds of North American Forests, USDA Agriculture Handbook 511 (1977), bluebird food paragraphs. Thomas G. Gentry, Nests and Eggs of Birds of the United States (1882), eastern bluebird. Public domain. Project Gutenberg #62678, #49172 and #45063.
Passages reproduced verbatim. Illustration placeholders, footnote markers, and the bulletin’s Latin-name footnotes have been removed; two OCR errors are corrected (“five clays” to “five days”, “lie is very attentive” to “he is very attentive”); wording, spelling and punctuation are otherwise as printed.
