Insects never have evolved complete immunity to birds. Camouflage and bitter taste, yes. Total defense, no.
We could use more birds.
Each year insect damage to Minnesota crops of any kind, including your garden, costs many millions of dollars. That's loss of income and cost of control measures.
Control alone is expensive, particularly when not all of the treated insects die. Survivors breed their resistance into the next bug generation. Bugs go back to the plants. Scientists go back to the lab.
Do our backyard birds — feeder birds, songbirds — make any contribution to insect control?
A pair of white-breasted nuthatches nested this spring in a tree cavity 20 feet from our deck. In early June the pair was feeding babies. I wanted to know the menu.
I watched the birds from a comfortable chair, coffee at hand until 5 p.m., after 5, not coffee. Tough job, but somebody, etc., etc. I used a camera, telephoto lens, tripod, cable release.
I have photos of bird bills filled with bugs of all kinds, from ants to moths, heavy on small caterpillars, and including what appeared to be a snail. It's difficult to identify the insects. Most of the offerings are mashed. The caterpillars tend toward green.
The snail actually was a semislug, delivered in a neat spiral shell. (Semislugs by design don't fit in their shells.) The parent nuthatch pounded the shell open and jerked out the slug. Semi-escargot.
The dominance of insects on the baby-bird menu was not news. Most if not all songbird species, even seed- and fruit-eaters, feed their young insects for fat and protein. If you grow from hatched egg to flying bird in three weeks or less, a proper diet is essential.
A website touting insects in your diet and mine said, "Insects are packed full of protein, beneficial fats, vitamins, minerals and prebiotic fiber." There you go.
The nuthatches came to the nest with food for their young about 15 times an hour, give or take. During the first week of June, when feeding was at a high point, daylight stretched more than 15 hours.
Fifteen feedings per hour for 15 hours — 225 insects per day based on my nonscientific research. Nuthatches reach maturity in 18 to 26 days. Let's say 21 days: at 225 insects per day, a probable 4,700 insects removed from our immediate neighborhood.
We had at least 13 other bird species nesting this spring on or near our wooded yard with its swampy pond. If those families were fed at the same rate as the nuthatches — that's another 61,000 insects.
These are rough calculations by a nonscientist. Even so, a ballpark number means a lot of bugs.
Think of this in terms of farm crops and other plants, apples to zinnias.
Can we place a value on the insect control birds provide in our state? I couldn't find a dollar number.
For certain, though, there's more to birds than a bright voice or a pretty face.
Read Jim Williams' birding blog at startribune.com/wingnut.
