JULY
2004

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

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!

 

Writer: Tom Turpin
Editor: Olivia Maddox