Food Habits of the Thrushes of the United StatesBeal, F. E. L. (Foster Ellenborough Lascelles)
Science
Food Habits of the Thrushes of the United States
Beal, F. E. L. (Foster Ellenborough Lascelles)
Birds; Thrushes -- Food
_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.
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