Paul A. Smith: Nest boxes provide boost to wood ducks

HORICON - On the surface, wood duck houses don't look like typical gift boxes.

They're just a few pieces of wood cobbled together to form a rectangular structure, including a roof and a baseball-sized opening, all mounted on a pole.

Oh, but what prizes they contain.

"Each one is like Christmas," said Jeff Bahls, a nest box expert and Horicon Bird Club president who works as a wildlife technician with the Department of Natural Resources. "And better yet, each one tells a story."

On Thursday Bahls led a "present opening" tour and work party at Horicon Marsh State Wildlife Area.

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Winter is prime time for maintenance of wood duck nest boxes. Not only have the birds migrated to southern locations, but frozen waters facilitate access to the sites.

With a group of four — Bahls, John Ley of Beaver Dam, Tom O'Malley of Delafield and me — we set out to open, investigate, document and clean 17 wood duck houses in the southwestern section of the property.

Ley and O'Malley are volunteers and members of the Horicon Marsh Bird Club and Friends of Horicon Marsh Education and Visitor Center.

We piled into a pickup truck and Bahls slowly drove along dike roads toward the remote nest box locations.

Bahls, 57, has been actively keeping wood duck houses for 22 years. He has about 100 elsewhere in Dodge County and helps maintain about 55 on the state land at Horicon.

"It's a winter job," Bahls said. "You just want to make sure to get it done before the ducks migrate back and start moving in."

The conditions Thursday were "just about perfect," Bahls said. The ground was mostly frozen, allowing the vehicle to travel easily over the grassy terrain.

The marsh itself was covered with ice strong enough to support our weight.

With significantly warmer weather in the forecast, we considered the timing of our outing fortunate.

Each box is a mystery holding clues from last year's breeding period. Although designed for wood ducks, hooded mergansers often use the structures, as do other bird species, such as screech owls, tree swallows and European starlings. Squirrels and other mammals sometimes take over, too.

The detective work begins by opening the box and carefully examining the contents. Nest box No. 13 was especially lucky.

"Well, this is interesting," Bahls said as he teased apart a layer of grass and feathers from the box. "Looks like we had three different species in here last year."

The box had 13 membranes from wood duck eggs, indicative of successful hatching, covered by grass and feathers of a tree swallow nest, all topped off by screech owl pellets.

Several boxes later, we found snake skin in the structure, the tell-tale sign a great-crested flycatcher nested there.

Of the 17 boxes, five had evidence of successful wood duck nesting, four were used by starlings, three hatched hooded mergansers and two were used by tree swallows, one by a screech owl and one by a great-crested flycatcher. One box was empty.

Each box was cleaned of all material from last year and a fresh bed of wood shavings was placed at the bottom. Data collected from each box will be added to NestWatch.org, a program of the Cornell Lab of Ornithology.

Woodies and a select few other ducks, including hooded mergansers, buffleheads and common goldeneyes, are cavity nesters.

The Horicon work in 2009 produced the first documented case of a bufflehead nesting in Wisconsin, Bahls said. Jack Bartholmai of Beaver Dam photographed the young buffleheads as they jumped out of the structure.

Proper nest box design is essential for successful hatching. The box should be ventilated so it does not overheat, should deter or prevent predators from entering, and must allow ducklings to climb out.

Bahls grew up in a hunting family. His father taught him early that if "you hunt, you gotta give back." He estimates he has helped hatch about 9,000 wood ducks over the last two decades.

The wood duck is a shining star in the pantheon of North American wildlife success stories.

Unregulated hunting and habitat loss through the late 1800s and early 1900s led some to predict the wood duck would go extinct.

However, the Migratory Bird Treaty Act of 1918 prohibited the hunting of wood ducks nationwide. In the 1930s, the use of artificial nest boxes helped the species recover.

By 1941, the woodie population was considered sufficiently robust and a hunting season was reopened.

The species has fared well in many eastern and Midwestern states, including Wisconsin. In 2016, the population of breeding wood ducks was estimated at 89,775, up 32% from 2015 and 12% above the long-term mean.

Bahls is a member of the Wood Duck Society, a Minnesota-based nonprofit organization that promotes education and conservation of the species. The group has developed a list of best practices for nest boxes, including instructions for building a proven, productive structure.

About 50% to 55% of the nest boxes at Horicon successfully hatch wood ducks in a typical year, Bahls said. Wood ducks typically hatch from mid- to late-May.

Several nest boxes are placed within sight of the Horicon Marsh Education and Visitor Center.

It can be argued the real gifts from these boxes reveal themselves in spring.

That's when ducklings produced in the structures follow the hen's lead and leap from the entrance hole.

It's one of the wonders of nature.

Last May, the scene played out to perfection.

Forty visitors were at the center as part of a Natural Resources Foundation field trip when Bahls saw the hen woodie jump out of one of the boxes.

He knew what to expect next. Within minutes, 20 squirming, downy ducklings dropped to earth.

The crowd couldn't believe their great fortune.

It was the payoff after many months of work and planning.

"You take care of the boxes in winter, then you wait for the ducks to come back," Bahls said. "Then the hen incubates for 30 days. Then, in maybe two minutes, they all jump. It's short but very sweet."

Horicon to host nest box seminar

Nest boxes help a variety of bird species produce offspring. In Wisconsin, nest boxes are commonly used to assist Eastern bluebirds, American kestrels and wood ducks.

On March 4, Horicon Marsh Education and Visitor Center will host a free seminar with presentations from birding and nest box experts. Attendees can learn how to properly place and maintain nest boxes, which boxes are right for their yards and what species of birds they can attract. Presentation topics include "Make Your Yard a Great Stopover Point" by Kim Grveles, "Sights Along a Nestbox Trail" by Jack Bartholmai and "Bluebirds and Nestboxes" by Steve Sample.

The event runs from 8:30 a.m. to 1 p.m. The visitor center is located at N7725 Highway 28 in Horicon.

For more information, call (920) 387-7890 or visit www.horiconmarsh.org.