Hen House: If You Build It, They Will Come
Prairie ‘Mallard Factories’ A Huge Success

By Jim Fisher, Director Delta Duck Production Program

As a green biologist back in February of 1991, it was a real treat working with Miles Ward, a third-generation member of Delta’s famous Ward family. Based on the enthusiasm and encouragement of Delta board member Jim Scheer of Illinois, Miles and I were about to try some new artificial nesting structures in the prairie potholes of Manitoba. 

We had no way of knowing that the 94 Hen Houses we “planted” in the ice that winter would eventually prove to be one of the most effective tools in waterfowl management.

Since then Delta, the Manitoba Habitat Heritage Corporation (MHHC) and others have applied Hen Houses in various locations in the pothole region and across the vast breeding grounds coast to coast.  No fewer than nine Delta graduate students have worked with Hen Houses as part of their fieldwork.

By next spring, Delta and its partners will have 3,000 Hen Houses in the field. Other management agencies, wildlife clubs and individuals have embraced Hen Houses, as well, resulting in several thousand additional structures coast to coast.

While wood duck boxes have been used extensively for several decades, it was only recently that Hen Houses became popular. Unlike wood ducks that nest in cavities, mallards typically nest on the ground. Hen Houses provide nest sites that are safer and therefore more productive. They are relatively simple to build and are easily installed and maintained. They cost between $20 and $40, but the value of watching a hen sitting safely inside is priceless.

Mallards are very opportunistic birds and make up over 95 percent of the occupants of Hen Houses. Other reported occupants include scaup, canvasback, redhead, blue-winged teal, black ducks and wood ducks.

While ground-nesting mallards are vulnerable to an array of predators, Hen Houses provide a much safer place to nest. Nest success in Hen Houses averages 80 percent, much higher than that experienced on the ground (between 5 to 20 percent). Like the wood duck box, Hen Houses have great appeal to those interested in getting involved in a hands-on local project that is a very cost effective way to enhance mallard production.

Since Delta’s involvement with Hen Houses began in 1991, we have learned a lot about them through our student research program. Some of the key findings include:

* Landing platforms (Extensions on the bottom of the roll ) are not needed.

* Low maintenance designs, including those made with carpet or wicker weave are used at lower rate than the original flax straw design.

* Usage rate per Hen House is the same when there are one or two Hen Houses per wetland and drops when there are four Hen Houses per wetland.

* Cost per fledged duck can be less than $5.

* High homing rates occur for mallards nesting in Hen Houses.

* Usage rates are correlated with grass cover, in other words use of Hen Houses is higher in areas with more surrounding grasslands.

Very Cost-Effective

Delta student Matt Chouinard estimated that it costs roughly $3 per fledged duck from Hen Houses in Manitoba.

Using rough calculations for a broader application for our Hen House program, we estimate that Hen Houses produce ducks at a cost of $5 to $9 per fledged bird.  Matt’s research sought to determine the ideal density of Hen Houses per wetland, using one, two or four Hen Houses per wetland. Matt studied both small wetland (less than one acre) and medium-sized wetland (one to three acres), and found that two Hen Houses per wetland were optimal for both pothole sizes.

Other studies around the Minnedosa pothole country in Manitoba—where predation rates on ground-nesting birds is extremely high—indicated that Hen Houses have been responsible for the vast majority of mallard production.

Student Dan Coulton found that roughly 25 percent of the mallards are nesting in Hen Houses and they are producing roughly 85 percent of the ducklings. His preliminary data revealed a homing rate of 90 percent for hens nesting in Hen Houses between 2002 and 2003.

This likely indicates an increase in hen survival as a result of nesting in Hen Houses. While nesting success in Dan’s Hen Houses is roughly 45 percent, it is much better than the ducks nesting on the ground. Ground-nesting ducks are averaging less than 2 percent over the past three years in the same area.

The Delta Duck Production Program

Kevin Ward and Jim Fisher standing in front of 350 Hen Houses in the Delta Hatchery this past winter – Kevin built these structures and they will be put out in Alberta, North Dakota and Manitoba.

Delta and its partners currently have 2,600 Hen Houses in the prairie pothole region, with another four Super Sites planned for North Dakota, Manitoba and Alberta, bringing our total to 3,000. 

Future expansion depends upon the level of donations from our membership, cooperating partners to deliver the program and matching funds from our partners. Delta matches each donation through the North American Wetlands Conservation Act (NAWCA).

In addition to the numerous individual Delta members who have made donations to the program, Delta has many partners in both funding and delivery of the program. Some of the agencies involved with the program include the MHHC, Alberta Conservation Association, the North Dakota Game and Fish Department and several Wetland Management Districts of the US Fish and Wildlife Service. 

“With a 64 percent usage rate and 85 percent success last winter, we are very excited about the high production of mallards from our Hen Houses in west-central Minnesota” says Thomas House, of Melby.  Their wildlife group–The Pioneer Heritage Conservation Trust—built and installed 225 Hen Houses in a five-county area near Evansville over the past several years. They have a number of volunteers who help out on several Sundays throughout the winter to build and maintain structures and expand the project beyond the original focus area.

Ken Zolnoski of Cheektowaga, NY and the Finger Lake & Western New York Waterfowl Association reports on the use of an ingenious modified version of the Hen House, one that uses three half-inch EMT conduits for support.  The Association has been successfully using Hen Houses for about a decade and maintains just over 200 each winter in the Montezuma Wetlands area and other areas around the Finger Lakes.  They have data going back to 1991 and average 60 percent usage and 90 percent success.

Delta chapters have also jumped aboard the Hen House bandwagon, with many of them building and installing Hen Houses and wood duck boxes. The Whistling Wings Chapter of Western Pennsylvania has been using some of their Waterfowl Heritage Funds (a share of net proceeds from their local Delta fundraiser) to install wood duck boxes and Hen Houses. To date they have installed 15 wood duck boxes and 12 Hen Houses, and while only one Hen House hatched a clutch of ducklings the group will continue its efforts to learn more about them locally.

Tom Dufour and the Delta Chapter from Baton Rouge have built and delivered 100 Hen Houses in each of the past two years to our program in North Dakota. This is a great example of linking the south with positive and tangible efforts on the breeding grounds.

Charles Close and Mark Knaupp, of Salem, OR and their  local group put out 19 Hen Houses last year and had 80 percent use in the first year and as a result of this they have bumped the number up to 100 for the current breeding season and have the state government involved as well.

Delta has additional information on Hen Houses on its website. Included there is a video on how to construct and maintain them, designs for those interested in making your own, where to buy them and other information.

While there are many effective designs, the design we currently use—which is a modified version of the MHHC design—works just fine. This is a simple design, involving three welds and three holes to be drilled. The rest is easy.

Delta students have had excellent luck with the original design, made with flax straw in the rolled portion and brome grass inside the roll where the hen lays her eggs. Initial use rates in artificial materials seem to be about half those found in flax structures.  We have tested landing platforms—12-inch extensions beyond the roll—where ducks could perch before entering, and found they have no influence on usage rates. We have also tested the number of Hen Houses per wetlands on wetlands less than one acre to three acres in size and found no difference in usage rates between one and two Hen Houses per wetland, but a drop in usage rates when four were installed. Ensuring Success:

Usage rates vary greatly between regions.  Many areas have experienced 80 percent usage rates after a few years, while some areas and regions have usage rates near zero. The reason for this is unknown, but whenever considering a project in a new area, we recommend starting with a small number of Hen Houses and evaluating how well they do before launching into a large and expensive program.

Some possible reasons for lack of success could include things like:

* design – usage rates are lower with artificial structures

* nesting material – need to have 1⁄2 to 2/3 of the inside filled with leafy grass nesting material

* location – are they located in an area where mallards are nesting?

We have a perfect example of use on the Delta Marsh, our Canadian headquarters in Manitoba. On the north side of the 50,000-acre marsh we have very poor usage, while on the south side we have very good usage. This may have something to do with the south side having plenty of grasslands and adjacent farmlands, while the north side is a forested ridge and Lake Manitoba.