Kevin Ringelman | 5/23/2019 3:07:26 PM
Lizzi Bonczek and Kevin Ringelman
Every winter the coastal marshes and rice fields of southern Louisiana host millions of migratory waterfowl. Most of these are only temporary visitors and migrate north in the spring. But one species, the mottled duck, is a unique nonmigratory duck found only along the western Gulf Coast and peninsular Florida. Louisiana’s local population of mottled ducks has declined over the past 40 years, and the count recorded in the 2018 Louisiana breeding survey was the lowest on record. Declines in mottled ducks go hand-in-hand with marsh loss and degradation. Louisiana wetlands constitute about 40% of the total coastal marsh acreage for the entire United States; however, Louisiana is experiencing about 80% of the marsh loss. As a resident species, mottled ducks depend on coastal marsh and rice fields to meet all of their needs throughout the annual cycle, and so loss of these habitats has acute negative effects.
Although harvest during the hunting season may seem like the most critical time for mottled duck populations, adult survival is actually on par with other species of waterfowl whose populations are stable. Instead, recruitment, or the number of young produced each year, is the most likely factor limiting population growth. Pulling off a successful nest is no small feat in the waterfowl world. A female must be in good enough body condition, with healthy grasslands adjacent to wetlands, to even make the attempt. Then, the female is — as the saying goes — a sitting duck for more than a month, exposed to numerous predators; around 80% of nests are destroyed by predators. Finally, ducklings must navigate the same predation gauntlet for another month before they can fly.
Studying the breeding biology of mottled ducks is difficult. They are wary by nature (just ask any duck hunter) and can potentially nest anywhere in the vast and largely inaccessible marshes of Louisiana. Without a good systematic way to locate and monitor nests, we are marking females with GPS transmitters and letting the birds themselves lead us to their nesting locations. Catching these ducks is almost impossible for most of the year. Thankfully, for about a month each summer, they molt their wing feathers and are flightless, and that is our only chance to capture them. During the week of the new moon in August and September, we brave the endless mosquitos and red alligator eye shine and round up molting mottled ducks from airboats in the middle of the moonless night. Zooming around in circles spotlighting ducks and trying to grab them from the side of the airboat with bare hands is exactly as wild as it sounds. After capture, adult females receive a transmitter, fit like a backpack and secured with elastic, which logs the individual’s location every two hours and sends it to our computers through the cellular network
So far, we have deployed transmitters on 130 female mottled ducks in southwest Louisiana, logging more than 100,000 total locations. Most birds do not travel far once they have chosen a spot they like, often settling in a swath of marsh or a rice field. By monitoring these ducks daily, we have become well-acquainted with each individual bird, although sometimes their behavior results in more questions than answers: one duck settled in a forested wetlands patch (unusual for a coastal species), while another duck stayed exclusively on Rockefeller Wildlife Refuge for a full year before randomly picking up and flying to Texas.
Other birds have led us to their nests, just as we hoped they would. Take mottled duck No. 54, for example. In the year and a half since capture, she has survived a hurricane and tropical storms, two hunting seasons, and countless interactions with mammalian, avian and reptilian predators. She was one of six females to initiate a nest this past breeding season and one of two females whose nest hatched, even leading her ducklings across busy Louisiana Highway 82 to a wetland she had visited the day before her eggs hatched. She actually nested over the water by building her nest up using pieces of the surrounding vegetation; this strategy had not previously been observed in mottled ducks, which typically nest in grassy upland areas.
GPS transmitters have allowed us to gather more data than we could ever imagine. In addition to examining nesting ecology, we can study movement in response to storms and hunting pressure, as well as evaluate habitat selection and adult survival. This information can be used to direct conservation strategies that will help improve mottled duck populations and ensure that this charismatic emblem of the Gulf Coast persists for future generations to enjoy.
This article appears in the spring 2019 issue of Louisiana Agriculture.
Lizzi Bonczek and Kevin Ringelman fit an adult female mottled duck with a receiver in a backpack secured with elastic, which logs the individual’s location every two hours and transmits this information to computers through the cellular network. Photo by Madelyn McFarland
Mottled duck. Photo by Jacob Bushaw