Wood Ducks Love Wetlands

By Nancy Roeper

Have you ever wondered how wood ducks got their common name? Wood ducks (Aix sponsa) are among the few waterfowl species that perch and nest in trees (hence, “wood”). They cannot make their own nesting cavities, though, so they rely on dead trees or places where a branch has broken off and the tree’s heartwood has rotted. Their preferred habitats are bottomland forests, swamps, freshwater marshes, and beaver ponds.

The wetlands and beaver ponds of Huntley Meadows Park (HMP) in Fairfax County provide a great home for wood ducks. To provide nesting sites to supplement natural cavities, volunteers help maintain and monitor 16 artificial wooden nest boxes on poles that are equipped with a galvanized metal cone or collar that prevents snakes and other predators from entering the box.

Other protective measures include placing the nest boxes well away from vegetation that snakes and raccoons can use to get around the cones, and spring-loaded hooks to latch the access doors to confound raccoons. Raccoons are surprisingly adept at opening latches and slide bolts, and turning knobs, and manipulating multi-step locking mechanisms. Their front paws have a very high concentration of sensory receptors that give them a remarkable level of dexterity. So far, the spring-loaded hooks have kept them out of the nest boxes!

As an ARMN and HMP volunteer, I’m part of a small team that monitors the nest boxes.  In early spring, we wade into the wetlands to add fresh wood shavings to the boxes, first removing any old or damp shavings. We note whether nearby vegetation needs trimming, latches need replacing, or other maintenance is needed to keep the boxes functional.

Wood ducks have been nesting in wooden nest boxes since about the 1930s. In the late 19^th century, wood ducks, and many other species of migratory waterfowl, underwent a dramatic decline primarily due to hunting (both sport (for recreation) and market (for commercial sales), and the draining of large swaths of hardwood bottomland forests and inland wetlands that were then converted to agriculture. To increase waterfowl breeding success, the Bureau of Biological Survey (precursor to the U.S. Fish and Wildlife Service) started an artificial nest box program. The first boxes were installed at Chautauqua National Wildlife Refuge in central Illinois. Over time, wildlife managers realized that the boxes were particularly popular with wood ducks. Since those early efforts, thousands of wood duck boxes have been built and installed by conservation agencies and private citizens.

During the height of the egg-laying season, we check the boxes weekly looking for signs of use: a depression in the wood shavings, soft feathers that females have pulled from their breasts to line the nest, or best of all: eggs!  Females may lay six to sixteen eggs in a nest and often raise two broods in one year.

But another duck species at the Park also likes to use the nest boxes: hooded mergansers (Lophodytes cucullatus). Both mergansers and wood ducks may lay eggs in boxes where an individual of the other (or same) species has already laid eggs. This is a type of brood parasitism. The Park doesn’t play favorites, though; whomever lays eggs in a nest box or chooses to sit on them and hatch them, is up to the wood ducks and mergansers.

Our monitoring protocols call for checking on all the eggs in a nest. We can distinguish wood duck eggs from hooded merganser eggs by color, size, and shape. Wood duck eggs are smaller, oval, and tan/beige, while hooded merganser eggs are larger, rounder, and whiter. Both wood ducks and merganser nestlings take up to 70 days to fledge.

The HMP wetlands and beaver ponds can be challenging to navigate. We never go out alone to check on boxes because it is easy to get tripped up by submerged logs and other vegetation. And we rely on substantial hiking poles to help keep our balance as we frequently need to exert great force to extract our feet from thick mud.

As the season progresses, we make fewer trips to the boxes because we don’t want to disturb the nesting females. If the female does not flush from the box when we approach, we just leave her be. But we continue to check on the eggs and look for signs of predation when we can.

I consider it a privilege to be out in the wetlands of HMP in my waders in the morning, seeing how rapidly the season evolves with each passing week, enjoying the birds, vegetation, and other wildlife that call the Park home, and helping to protect our native wood ducks.