|
07-22-04
Insect Eating is for the Birds
It's a bird-eat-bug world out there! Insects are good food items, and
birds need to eat. So, it probably doesn't surprise anyone that insect
predation is a common habit of birds.
Most people have probably witnessed birds pursuing an insect meal. Woodpeckers
make holes in wood to find insects. Starlings walking in flocks on the
lawn are searching for insects. Swallows, martins and swifts pursue their
insect meals while flying.
Some birds are entirely insectivorous -- the term used to describe animals
and plants that chow down on insects. Swallows, for example, feed only
on insects. But most birds are general feeders, eating a combination of
fruits, seeds and insects.
According to Gilbert Waldbauer, in his book "The Birder's Bug Book,"
ecologists divide the insect-eating habits of birds into guilds. Guilds
are described as groups of species that behave in similar ways.
So, guilds of insect-eating birds include the following. Leaf gleaners
are those birds, such as the warblers, that pick insects off leaves. Then,
there are the bark gleaners, such as nuthatches. Woodpeckers are classified
as wood and bark probers.
Another group is classified as air salliers. The air salliers sit on
a perch and then fly out to catch an insect on the wing. These birds include
the fly catchers. The final guild is described as gleaners of aerial plankton.
This group includes swallows and swifts.
In reality, most birds catch their insect prey in a variety of ways.
For instance, the bluebirds around our farm generally seem to be leaf
gleaners, but they will certainly sally off the fence to catch an insect
on the wing.
One interesting habit of insect-eating birds is that some birds will
feed their young exclusively insects but feed on a high percentage of
plant material themselves. Grackles do this. They feed the offspring entirely
an insect diet, but only a small percentage of their food is insects.
The reason might be that the rapidly growing young require a diet high
in protein, which the insects supply.
The insect-eating habit of birds should be a delight to most homeowners
and gardeners. After all, the birds are consuming some of the insects
that are eating our plants. In a couple of well-publicized historical
incidents, birds apparently saved the day from plant-devouring insect
hoards. In Australia, crows several times have eaten enough grasshoppers
to save crops. In Utah, sea gulls ate the grasshoppers, incorrectly called
Mormon crickets, which were destroying the range and vegetable plants.
The exact number of insects consumed by birds is unknown. In general,
any species of an insect-eating bird consumes several kinds of insects.
One study showed that northern cardinals consumed 51 kinds of beetles,
4 types of grasshoppers, 12 types of Homoptera, including leaf hoppers,
cicadas and aphids, and some termites, ants, flies and dragonflies.
Most birds will catch the insects that are available. So, when there
are high numbers of one insect species, such as big outbreaks of a kind
of caterpillar or periodical cicadas, many birds will have a feast. It
is almost as if Mother Nature has rung the dinner bell for insect-eating
birds. But, in spite of the number of insects that end up as meals for
birds, there are always enough left to keep the insect population going.
That is what is known as the balance of nature!
|
