What Happens in the Box . . .

Spending a day (or two) following in the footsteps of a wood duck biologist

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The wood duck is an iconic bird widely known for its beauty, which has long inspired artists, birders, and wildlife photographers. The stunning birds have also long been favored by hunters across the country, and today make up approximately 10% of the national duck harvest annually. To waterfowl hunters, the gaudy bird is considered excellent table fare and is often a treasured prize to drop off to the taxidermist.

During the late 1800s and early 1900s, this esteem—combined with deforestation and habitat loss, as well as the plumage market of the time—nearly drove the wood duck population to extinction. The 1918 Migratory Bird Treaty Act prohibited the hunting of wood ducks, and populations started to rebound during the 1920s.

The United States Fish & Wildlife Service’s first wood duck nest box programs began in the 1930s in the Chautauqua National Wildlife Refuge in Illinois, fueling the steady national increase in the population, even allowing for hunting seasons to be re-opened in 1941. Today, Ducks Unlimited estimates some 300,000 nest boxes exist in North America, producing 100,000 ducklings annually.

In the late 1980s, though, studies indicated reduced populations in the Southeast region, largely due to habitat loss. As a result, the Louisiana Department of Wildlife and Fisheries launched their own wood duck nesting box program in 1990, placing boxes in wildlife management areas, state parks, and properties managed by the U.S. Army Corps of Engineers—as well as some private wetlands. Former Louisiana Department of Wildlife and Fisheries Waterfowl Program Manager Larry Reynolds said that as of 2022 the department currently maintains an estimated 1,750 nest boxes, with a goal of reaching two thousand.

Over the years, these initiatives have allowed scientists to study things like duckling production and survival, box placement and maintenance, use, and brood parasitism (the frequency at which wood ducks lay their eggs in other birds’ nests, so that the other bird ends up raising their young). However, few studies attempted to extensively measure actual recruitment (the number of mother ducks and ducklings that survive subsequent breeding seasons) of this species until now.

The Nemours Wildlife Foundation study, which involves eight southeastern states including Louisiana, was born out of a 2018 meeting hosted by the Nemours Wildlife Foundation located in Yemassee, South Carolina, then followed by a pilot study in 2019 on the Santee Wildlife Refuge near Summerton, South Carolina. The multi-year research project, which is titled “Regional Examination of the Contribution of Nest Boxes to Wood Duck Recruitment in Southeast and Mid-Atlantic States,” looks to provide new information that will enhance management decision-making. Moreover, it will help states evaluate the effectiveness of existing nest box programs, and determine whether to continue, terminate, alter, or even initiate altogether new programs.

Reynolds said the LDWF jumped at the chance to participate in the Nemours study—for reasons even beyond the Foundation’s primary initiative to study recruitment. A structured nest box evaluation program had been on the department’s long-term priority list, he explained, but up to this point one had never been conducted. One major question is whether or not the boxes “contribute positively to [wood duck] populations in areas with sufficient nest cavities, or are they just a population sink?” He pointed out that biologists use the term “sink” to describe situations where birds are attracted to habitats where they cannot be successful. An example he used is a sea of farmland with an over-abundant predator population.

[Read more from John Flores, here: "The Cazan Lake Ballet"] 

In Louisiana’s case, some scientists worry that ducklings hatched in wood duck boxes located in swamp and marsh wetland habitats may simply be feeding the alligators and their eggs feeding snakes. Another objective Reynolds says the department was hoping to learn more about through the study is whether hens nesting in wood duck boxes produce hens that nest in wood duck boxes in future generations.

In 2021, I spent two full days in the field with Dylan Bakner, a PhD student with the LSU AgCenter, learning about the wood duck recruitment study. The first day was during the latter part of April, checking nest boxes. The second took place several months later in early August.

Bakner’s role in the study has been focused on the effects an expanding population of black-bellied whistling ducks have had on the wood duck nest box program, addressing concerns that these birds might be competing with wood ducks for habitat—which could lead to parasitism, where poor wood duck duckling survival could be a concern.

For the past twenty to thirty years, the black-bellied whistling duck has been expanding its range further and further north from Mexico and south Texas, where now they appear to be firmly established as year-round residents in Louisiana. During the winter, large flocks of these whistling ducks hang out in the greater New Orleans area in places like Lafreniere and Audubon Parks, as well as across the Mississippi River in Westwego, where there is a ready-made food source and safe refuge around grain elevators. In the spring they leave their urban settings and disperse across the Louisiana landscape to nest, potentially in direct competition with wood ducks.

One of the wood duck nest box study’s “Anticipated Outcomes” is to gain new information on the nesting ecology of black-bellied whistling ducks, which may open avenues of applied scientific inquiry relevant to the management of cavity-nesting species in Louisiana. Of the estimated 1750 wood duck nest boxes the LDWF manages in its Wildlife Management Areas, Bakner’s research involves around three hundred

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Bakner said of the black-bellied whistling ducks, “We don’t know anything about these guys. [Until very recently] there has not been a single study done in the southeastern United States focusing on black-bellied whistling ducks. All of the studies that have been done regarding breeding whistling ducks took place on the northern end of their breeding range in the ‘60s and ‘70s, which was southern Texas.”

The boxes we checked were all located on Sherburne Wildlife Management Area, which rests inside the boundaries of the vast Atchafalaya Basin, the largest contiguous hardwood swamp in the United States. We spent our time on the complex’s North and South farms, where LDWF manages large freshwater impoundments, which are drawn down in mid-summer to enhance the growth of wetland plants as forage for wintering waterfowl. During the drawdown period, the shallow water and mudflats act as a magnet to wading birds such as egrets, ibises, roseate spoonbills, and herons, as well as shorebirds.

Bakner loaded up an RTV we’d be using to traverse the impoundment levees, where the LDWF placed wood duck nest boxes. At the first box, I watched him creep quietly up to it, so as not to alert the bird that might be sitting on eggs inside, then quickly plug the entrance hole using a Nerf football. (The process doesn’t always work. We had several skittish birds flush out of the entrance hole just as we approached the box in the RTV, or while walking up to them.) After the hole was plugged, Bakner set up a ladder to lift the lid to see if the box was occupied. If a bird was present, Bakner would capture it.

The nest boxes in Bakner’s study areas are monitored on a weekly basis, and most of the birds captured during our trip had already been banded and tagged. In those cases, their information was simply recorded and the bird was released. Whenever they hadn’t been previously banded and tagged, he swiftly did so.

After processing the adult birds’ information, Bakner moved on to each nest’s eggs, for which he took and recorded morphological measurements consisting of length, width, and mass as well the quantity of eggs in each nest. Each egg was then inscribed with a felt marker and given a specific number to identify it on subsequent visits.

While Bakner handled eggs from one of the nest boxes, he explained how the incubation data collected each week was critical in trying to predict when the nests would hatch. “Once it approaches within three days of its expected hatch date, we’ll go visit that nest each day with hopes of opening a box and having it full of ducklings, which we’ll PIT and web tag,” said Bakner.

PIT (Passive Integrated Transponders) tags are essentially the same type of microchip used in family pets such as dogs and cats. By scanning the chip, pets can be identified and returned to their owner. Likewise, when biologists encounter a PIT-tagged wood duck, a handheld scanner can be passed over the bird, which will display an identifying number.

PIT tags are believed to be more accurate than traditional web tags, because of the fragility of the web on a duck’s foot. For ducklings, it’s worse, and many of their web tags end up lost.

For the study, half of each brood are web tagged, and the other half PIT tagged. By dividing the tagging methods into two groups, biologists hope to compare and learn more about their respective recovery rates. When Bakner discovered black-bellied whistling ducks in a nest, though, all of those ducklings received PIT tags.

“Our number one objective is to study wood duck recruitment,” said Backner. “So, capturing these ducklings and tagging them, and then seeing how many of those females survive until next year to breeding age, accomplishes some of that.”

As of July 2022, Bakner and his team had marked and recorded 743 adult wood duck hens and 3,749 wood duck ducklings, as well as 258 adult black-bellied whistling ducks, and 1,213 whistling duck ducklings.

At the end of each field day, participating researchers like Bakner enter their data into an app, which is then synchronized and uploaded to the main database that Nemours is managing.

One of the major findings at study sites across all of the participating states was that wood duck eggs frequently go missing, though the nests are still hatching out. Bakner said, “It was like some predator was showing up, picking off one egg and doing that X number of times throughout the nest’s life. The nests were still hatching and doing fine, but we weren’t sure how the eggs were going missing.”

By installing game trail cameras inside some of the nest boxes and adapting a fisheye lens made for iPhones to them, Bakner was able to quickly solve the mystery.  He learned eggs become damaged from a variety of reasons, including altercations. One video he captured showed two wood duck hens physically fighting with one another as they both tried to lay their eggs in the same nest box. In another video, he recorded a hen wood duck leaving her nest box for an incubation break. Soon after, a red-bellied woodpecker came in and started pecking and feeding on an egg.

What Bakner discovered is when wood duck hens return to the nest box, the first thing they do is assess the nest, inspecting nearly every egg. If one is found broken, they’ll take their upper and lower mandible and shove it in the egg, pick it up, and fly out of the box with it.

Through his research, Bakner has been especially focused on determining just how much overlap there is in the wood duck and black-bellied whistling duck breeding season. Essentially, he said, when it comes to nest initiation dates (meaning the first day that a wood duck lays an egg and the first day a black-bellied whistling duck lays an egg), there is a ninety-three-day period of overlap, where both species are nesting.

As a result, there are some mixed clutches. Bakner has documented wood ducks hatching out black-bellied whistling duck eggs, as well as their own, and black-bellied whistling ducks hatching out wood duck eggs, as well as their own.

Based on the data Bakner compiled through 2020, of all of the wood duck eggs observed that hatched, 13% of them came from mixed clutches. And of all the black-bellied whistling duck eggs observed that hatched, 32% of them hatched from mixed clutches.

So the question becomes: is the overlap in nesting periods influencing or helping wood duck productivity? Another question might be, are the two species influencing or helping each other? In the case of black-bellied whistling ducks, it may not be such a bad idea to try and target a nest with eggs from both species, Bakner said.

“We just don’t know anything about black-bellied whistling ducks. There’s a single paper—one paper that notes two wood duck nests, where somebody observed whistling duck eggs being incubated by the wood duck,” said Bakner.

Another unique observation Bakner has made is that despite the many mixed clutches he has observed,  he has never seen a mixed brood outside of the box. “It’s like they jump from the box, and then I see whistling duck ducklings with whistling duck mom and dads. And, I see wood duck ducklings with wood duck mom and dads. I never see a mixed brood, and yet I have evidence of them surviving.”

All in all, Bakner is plowing a lot of new ground as he studies the ecology of black-bellied whistling ducks as part of the regional wood duck nest box recruitment project. Bakner’s field work was completed during the spring of 2022 and will be published in July 2023. 

Learn more about the Nemours Wildlife Foundation at nemourswildlifefoundaton.org and about LDWF’s Wood Duck Nesting Box Program at wlf.louisiana.gov.