Last May, a wren came over and tossed some sticks in the little birdhouse hanging in my backyard. It burst into the Coldwell-Banker theme song, and we eagerly anticipated baby birds. Then he left and never came back; our house didn’t pass muster with the missus.

A chapter in the new edition of Carrol Henderson’s "Woodworking for Wildlife" explains why, exposing the design flaws that make many commercially available birdhouses duds or deathtraps. Ours was complete junk, designed to please humans, not birds. But thanks in part to Henderson, who began publishing birdhouse patterns 30 years ago, the Minnesota landscape is dotted with thousands, if not hundreds of thousands, of proper birdhouses. Some of these projects, such as the Peterson bluebird house, have been key to restoring species impacted by human development.

"Woodworking for Wildlife" has sold 90,000 copies since Henderson, supervisor of the DNR’s nongame wildlife program, first reworked his instructional pamphlet into a 48-page book in the mid-1980s. It grew to 112 pages in 1992, and has just been reissued as a 164-pager that includes bird-by-bird house plans, species trivia, natural-history information and gorgeous photographs of birds, eggs, and nest boxes in use.

"They say that my books have legs because they keep moving among many readers," says Henderson, whose other hot title is "Landscaping for Wildlife"; it has sold nearly 90,000 copies and is enjoying a revival as green-minded homeowners transform their "dead zone" lawns with wildlife-friendly native plantings. "People tell me that they have literally worn the covers off my books, or that the books got borrowed by neighbors and never came back. It is gratifying to reach so many people in a way that benefits wildlife for the future."

The house plans are incredibly simple, and many can be made from a single board. Plus, they can make a real difference to species in peril. "The Peterson bluebird house has had an enormous impact on helping bluebirds, as well as incidental benefits for chickadees, tree swallows and house wrens. There are many thousands of those nest boxes across the countryside," says Henderson. "Nest boxes have made a great difference for wood ducks, and have incidentally benefitted many other species as well."

However, ever the DNR guy, he says, "nest boxes alone are not the total answer. People need to provide plantings for wildlife and they should contribute to conservation organizations that make a difference for preserving habitat — like Ducks Unlimited and the Nature Conservancy. They can buy state and federal duck stamps, and of course, they need to remember to donate to the Nongame Wildlife Checkoff on their state tax forms.”

A few species are in particular danger now. Henderson says flicker numbers are dwindling a dramatic 5 percent per year because of lawn chemicals. Many older nesting boxes have become uninhabitable or have been taken over by non-native house sparrows. "There is a lot of momentum building for helping purple martins by putting out the new martin houses. Most older martin houses are not managed properly and are not in the proper setting to be effective," he says.

Henderson and his wife, Ethelle, live in Blaine, and during the 32 years they’ve owned their home, they’ve practiced the advice he gives his readers. "We have planted many trees, shrubs and perennials for wildlife over the years, reducing the amount of lawn and increasing the permanent plantings that provide wildlife benefits year-round. We have from 8 to 12 feeders in place around the yard, depending on the time of year; two bird baths; and a nest box for chickadees, tree swallows, or wrens."

But his influence extends far beyond his own plot. He’s led birding trips and conservation efforts in China, Costa Rica, Tanzania and Russia, among other places. Another one of his books, "Landscaping for Wildlife and Water Quality," has helped Minnesota cabin owners combat erosion, water contamination and fish declines. Who says a book can’t make a difference? It will at my house; a new wren box is already in the works.

Carrol Henderson will sign copies of his books on Aug. 14 from 11:30 a.m. to 1 p.m. at Minnesota’s Bookstore, 660 Olive St., St. Paul.