BRAINERD, MINN. — Minnesotans with eyes and ears toward the outdoors likely know about the recent passing of Don (Duckman) Helmeke. Duckman had a passion for waterfowl -- in particular wood ducks -- and always was working diligently on various conservation efforts.

Unfortunately for me, I didn't know Duckman well. The first time we met was at a gathering of the Wood Duck Society. I had purchased from Duckman a handful of special washers he designed to ease the chore of mounting wood duck boxes to trees. That was more than a decade ago.

Back then most wood duck boxes were set in trees, and Duckman's washer was an especially valuable aid in achieving that chore. What's unique about the washer is that it has a keyhole-shaped center. To mount a wood duck box to a tree, a person using the washer simply ran a bolt into the tree, leaving about 2 inches of the bolt exposed.

Then a hole slightly larger than the bolt head was drilled into the back of the wood duck box at the mounting point. The box then slipped onto the bolt. The bolt held the weight of the box and allowed both hands to be free while a Duckman washer was placed over the exposed bolt head inside the box. The washer was then slipped down until the keyhole section of the washer contacted the shaft of the bolt. Then the bolt was tightened. Simple, but effective.

An added bonus to using the Duckman washer was that each year while cleaning out the boxes, the bolt holding the box to the tree could be loosened a bit as the tree grew.

Now, however, most wood duck experts suggest boxes be mounted on predator-proof poles instead of trees, and thus the Duckman washers are not needed.

For 14 years, I've been maintaining and monitoring a dozen or so wood duck nesting boxes I placed on my property south of Brainerd. Wood ducks, as well as other cavity-nesting species such as hooded mergansers and kestrels, have successfully raised families in the homes I have provided for them.

During those years, I occasionally had trouble with predators -- mostly raccoons.

That is, until two years ago.

In one three- or four-day period, eight nesting boxes were invaded. In all cases, the eggs were destroyed, and in some instances, even the hen was killed.

My wood duck nesting boxes were placed in trees, and in the past I had made no attempt to deter predators. That, I realized, had to change.

Why the sudden shift in the amount of predator problems?

During past years, my occasional predator troubles could always be linked to raccoons. But in recent years, the fisher, a mink-like animal, has become relatively common in central Minnesota, and I suspect that was the predator responsible for invading my nesting boxes last spring. I have seen several fishers on and near my land.

Despite their name, fishers rarely eat fish. They are agile animals and can climb trees like a red squirrel.

I am not "anti-predator." Predators are a necessary component of a healthy environment. But I decided I wasn't going to continue to provide them with easy access to a smorgasbord of wood ducks and wood duck eggs.

To predator-proof my wood duck nesting boxes, I adopted the plan endorsed by the Wood Duck Society. Check out their website for complete instructions and patterns for building and placing predator-proof nesting boxes. The site also provides information on where to purchase the necessary metal cones and brackets.

The Society recommends placing the boxes on posts instead of trees, and to use a galvanized sheet metal cone to turn back predators that attempt to climb up to the boxes. Contrary to popular belief, higher is not better when it comes to placing wood duck nesting boxes. In fact, according to the Wood Duck Society, some studies have shown wood duck hens prefer lower-mounted boxes.

Another plus to mounting boxes on poles: no ladders and no climbing. Boxes can be maintained and monitored with both feet on the ground.

I will be adding two more wood duck boxes to my property soon. Now is a good time to do so, prior to ice-out. The task will be achieved when I clean out my existing boxes. I still have a few of Duckman's washers, and will be using them even though they are no longer necessary with my new pole mounted system.

I think Duckman would like that.

Bill Marchel, an outdoors columnist and photographer, lives near Brainerd.