Wood Ducks and Boxes
   . . . Build Them and They Will Come!

An annual winter activity

by
Tim Thompson, Wildlife Biologist
Coralville Wildlife Unit 
Iowa City, Iowa

Wood ducks are one of the most beautiful waterfowl species we have in Iowa. But they were in danger of extinction in the early 1900s due to timber clearing and unregulated hunting.  Laws were passed to regulate duck hunting but habitat losses continued. 

Wildlife biologists realized that wood ducks nest in tree cavities. It would take years to re-establish mature forests.  So, biologists tried artificial nesting structures and found they worked! Wood ducks have made such a successful recovery that they are now one of Iowa’s most common nesting ducks and are one of the top three duck species in the duck hunters bag.

The Coralville Wildlife Unit personnel construct and maintain hundreds of wood duck nest boxes on their public areas. After major flooding in 1993, more than half of our nest boxes were destroyed. Since we had been experiencing very high nest loss to raccoons, we redesigned our placement of boxes.  Instead of attaching boxes to trees or wooden posts with predator guards, we switched to using metal posts. Brackets are made with a slightly greater diameter pipe.  The brackets are attached to the wood duck box and then slid over the pole and securely fastened with a bolt on the bracket to the metal pole. To prevent predators from easily accessing the box, a three-foot long section of PVC plastic pipe is put over the pole between the box and the ground. The plastic pipe sits on a bracket to hold it in place, but it is free to spin so a raccoon can not get a grip and climb up the pole. 

Over the last four years usage of nest boxes on the Coralville Wildlife Unit has ranged from 51 to 61 percent. Successful nest rates have ranged from 56 to 79 percent with the lower success rate occurring when there has been major flooding on the Coralville reservoir. The usual nest success rate for natural tree cavities is just 30 percent.

Perhaps now you're interested in perpetuating wood ducks on your own property.  Let’s get you started on the right track to having wood ducks on your land.  Do you have a pond, marsh or stream on your land? In good habitat, wood ducks may nest a mile or more from water. But, the closer to water, the better. 

The next step is to start your box construction. (Click on the diagram for a larger view) The traditional wooden box is a good style and is easy to build, but other variations will also work. Basic dimensions should be 12” x 12” and 24” high. The entrance hole should be approximately 16 to 18 inches from the bottom of the box. It is important to cut an elliptical hole 3” high by 4” wide. This is just the right size to allow wood ducks in but is too small for raccoons.  No perch or ledge is needed. 

The inside of the box must have a rough surface below the hole to allow the new ducklings a foothold to climb out. This can be done by attaching a hardware cloth strip below the hole. Drill some drain holes in the bottom of the box. Boxes can be painted or stained a natural color to make them last longer.

Next is the placement pole; I would suggest using a 1½” to 2” diameter metal pole. Attach the nest box using brackets as described earlier, or extend the back board of your nesting boxes 3” above and below the length of the actual box to give you room to use another attachment technique. This could be using “U” bolts to go around the pole and fasten through the top and bottom box extensions.  An extremely important last detail is using a predator guard such as the loose PVC pipe.

Now let’s get those boxes out. Boxes should be placed 4 to 5 feet above the normal high water level.  Water levels should be at least 18 to 36 inches deep. Look for potential wood duck roosting or loafing areas such as flooded willows, buttonbush, downed trees or emergent vegetation. Start by putting up your boxes in visible places with up to two boxes per wetland acre. As wood ducks start to use your boxes, you can put more on the shore in isolated locations. These should be at least 6 feet off the ground and now predator guards are an absolute must. Also, place the boxes away from overhanging tree branches.  Wood ducks have nested in cavities as high as 65 feet and as low as two feet off the ground or water. Studies have shown that inconspicuous boxes have higher nest success rates. 

When your box is up, add about 4 inches of wood shaving as nest material. Do not use fine sawdust because it holds too much moisture. Your whole project should be done before wood ducks start arriving in mid-March.

Yearly maintenance is a must to continue a successful program. This may just be a matter of cleaning out boxes and replacing the old wood shavings. However, repairs to the boxes, poles and guards may also be needed. Many critters may use the boxes besides wood ducks.  Some are other species of ducks, such as hooded merganser, goldeneye and bufflehead, will nest in wood duck boxes.  Others wildlife may also utilize your boxes including starlings, wrens, squirrels, mice, snakes, bees and wasps. If you check your boxes in the late winter, you shouldn’t find most boxes in use.

As well as being a good season for doing maintenance, winter is also a good time for evaluating the success of your boxes. In general, hen wood ducks lay one two-inch long, dull white colored egg per day. The average clutch size is 12 eggs but may range from 1 to 20 eggs. The hen incubates for approximately 30 days and the hatched ducklings leave the nest box within 24 hours after hatching. Broken eggshells in a box may indicate a successful hatch or predation. A papery membrane attached to a half section of shell indicates hatching success.  If a box contains shells with no membrane or just tiny shell fragments, a predator probably got the eggs. It is important to note that sometimes mice get into the boxes and eat the shells. And, if you find a box with many unhatched eggs, you have found a dump nest where more than one hen has laid eggs.

In summary, build your boxes correctly with the right size hole and a “climbing ladder” inside. Initially, place your boxes over water and add more boxes on shore as your population grows. Use predator guards! Maintain your boxes every year in late winter to insure they are ready for the ducks’ arrival. And remember, build them and they will come!

For further information about the construction and maintenance of wood duck nest boxes, and the Wildlife Bureau's work with wood ducks contact Tim Thompson at (319) 354-8343, or the wildlife biologist in the management unit you're interested in.

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