Wood Duck House: Box Size, Mounting Over Water and Yearly Upkeep

What a wood duck house is

Wood ducks nest in tree cavities, and a wood duck house is an artificial cavity set where natural ones are scarce. The Louisiana Department of Wildlife and Fisheries describes the wood duck as an obligate cavity nester and credits large-scale use of artificial nest cavities, along with restricted harvest, for the species’ recovery from very low numbers in the early 1900s. The first artificial cavities were used in Illinois in the late 1930s, according to the same sheet, which calls the boxes easy to build, inexpensive and highly effective. It adds that most boxes will be used the first year if they stand in suitable habitat and are reachable before the breeding season.

Searches for duck housing sometimes mean this box and sometimes a shelter for domestic ducks. The sources here cover only the first meaning, the nest box for wild wood ducks.

Dimensions where the sources differ

NestWatch, the Cornell Lab project, gives the entrance as 3 inches high by 4 inches wide, an inside depth of 24 inches, and a width and length of 8 and 9 1/4 inches as listed on its page. Louisiana’s plan cuts a 4 inch by 3 inch oval or a 4 inch round hole near the top of the front, and says inside dimensions typically range from 9 to 12 inches square. The entrance figures agree. The floor differs: roughly 8 to 9 1/4 inches on one page, 9 to 12 inches on the other. A builder following one source should follow it throughout, since the Louisiana plan is drawn with its own cut list.

Louisiana also notes that the overhanging roof must not impede the entrance. NestWatch says cedar works well and plastic boxes should be avoided because they can overheat. The Louisiana plan names rough-cut cypress or cedar as the most commonly used woods for weather resistance, and says a whole box can be cut from one 8 foot by 11 inch by 1 inch board.

The climb out

Newly hatched ducklings must reach the entrance. Louisiana says rough-cut wood is necessary so ducklings can use their sharp claws to climb and jump out, and that with smooth wood a section of hardware cloth or window screen stapled below the entrance gives them a footing. NestWatch describes the same fix: a strip of 1/4 inch mesh hardware cloth stapled inside, or a one foot deep section under the hole roughened with a chisel.

The leaving itself is brief. After the last egg is laid, incubation runs 29 to 31 days in Louisiana’s account, and all ducklings in a nest hatch within hours of each other. Once dry and strong, they leap from the nest to the water or the ground below, answering the hen’s calls. After hatching, Louisiana says, a duckling cannot fly for 50 days.

Mounting over or near water

Location is where the two sources give the most detail. NestWatch says a box can go on a post or pole in the water at least 3 feet above the high water mark, facing south or west. On land, it advises a site within 100 feet of water with no branches around the entrance. Its height range is 6 to 30 feet, boxes should face the water, and spacing between boxes is listed at 600 feet. It also suggests mounting the box so it leans slightly forward to shed rain.

Louisiana says boxes should be located over water in an area free of overhanging limbs and vines, on treated 4 inch by 4 inch posts or 2 inch metal pipe, preferably above water to reduce fire ant predation. It also stresses brood habitat. Ducklings cannot fly for 50 days, and a hen in a poor wetland may lead her brood overland, which the sheet calls very dangerous. It says backyard fishing ponds and city park ponds with open water and clean shorelines do not contribute significantly to productivity, while good brood habitat has emergent plants such as cattails and sedges and woody cover such as buttonbush and black willow.

Predator guards

Louisiana lists rat snakes and raccoons as the top predators of wood duck nests and says boxes should never be attached directly to a tree trunk, because climbers can then reach them. Its guard is a cone of 26-gauge galvanized sheet metal with a 2 foot radius, fixed to the pole directly under the box before the box is mounted. The bottom of the guard sits 3 feet 6 inches above ground or 2 feet above the water surface. The sheet states plainly that guards will not prevent fire ant predation. NestWatch says only that predator guards should be installed.

Shavings and spacing

NestWatch recommends 4 inches of wood shavings on the floor. Louisiana says at least 3 inches, specifying shavings and not sawdust, which the hen shapes into a nest bowl before lining it with her own breast feathers. For hooded mergansers, NestWatch gives 2 to 3 inches.

Spacing is tied to a problem both sources name. Cavity-nesting ducks lay eggs in other ducks’ nests. NestWatch says to avoid clustering boxes and to watch for clutches of 14 or more eggs or eggs of different colors, moving boxes farther apart if needed. Louisiana says average clutches are 12 eggs and a box with 15 or more is generally a dump nest, and that boxes should be visually isolated, with duplexes on one pole often producing dump nesting and abandoned nests.

Checking and cleaning

NestWatch advises monitoring in the early evening, when hens tend to leave to forage. After a brood is complete, it says to clean out the old material and add fresh shavings, since the wood duck is the only North American duck that regularly raises two broods in a season. Louisiana’s calendar is firmer: discard old nest material, eggshells, insect nests and unhatched eggs every year, add new shavings in December or January before the season, and add them again in April or May if the first nest has hatched. It says most nesting begins in March or April, with some experienced hens starting in early February.

Hooded mergansers and other tenants

Hooded mergansers use the same style of box. NestWatch lists the same 3 by 4 inch entrance for them, a height of 6 to 25 feet, spacing of 100 feet and installation by mid-March near or over water. It adds that merganser eggs can be told from wood duck eggs by their unusually thick shells. Louisiana names hooded mergansers, along with other wood ducks, as the biggest contributors to dump nesting.

Louisiana’s list of potential users also includes black-bellied whistling ducks, screech owls, flickers, prothonotary warblers, Carolina wrens, great crested flycatchers, eastern bluebirds, starlings, squirrels, raccoons, opossums and some insects. For boxes aimed at smaller species, the birdhouse guide and the plans section cover other designs.