The eastern bluebird[2] (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. 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.
[2] _Sialia sialis_.
[Illustration: Fig. 1.--Bluebird. Length, about 6½ inches.]
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.
Two species of bluebirds inhabit the Western States--the mountain
bluebird[3] and the western bluebird.[4] 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.
[3] _Sialia currucoides_.
[4] _Sialia mexicana_ subspecies.
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.