Story from the Field: Ducks of Suisun Marsh

Release Date:

Suisun Marsh in summer is typically heavy with fog, mosquitoes, and biting flies, but the sun casts sharp light across the water, beating back the usual unpleasantness as WERC volunteer Brock Riggs wades toward a study site on an early July morning. 

Site prep

Brock, a USGS volunteer, walks out to a future waterfowl trapping site with a bucket full of rice in hopes that it will attract waterfowl to the area. (Credit: Erika Sanchez-Chopitea, USGS. Public domain)

He’s carrying a bucket of rice, trying to balance it as water sloshes against the waders that rise halfway up his torso. As the rest of us — two field scientists and two employees from WERC Headquarters — watch from a nearby levee, Brock encounters an uneven part of the terrain and stumbles.

Desmond Mackell and Michael Fontana of the Dixon Field Station tell us that they know just how uncomfortable it can be to have muddy marsh water in their waders and boots. Luckily, Brock rights himself before water can enter his waders and continues toward his goal. He’ll spread the rice at a specific site, where the scientists will return regularly to check for signs of waterfowl taking the bait. If the bait is consistently eaten, they’ll set up a wide, wire mesh trap to capture waterfowl that frequent the area.

This field work is part of a larger, 10-year study led by WERC research wildlife biologists Dr. Josh Ackerman and Mike Casazza. With the partnership of local property owners who share the marshland, Dr. Ackerman and Casazza send out teams during the field season to learn about the movement patterns of waterfowl in Suisun. They’re interested in three species in particular: gadwalls (Anas strepera), mallards (Anas platyrhynchos), and cinnamon teals (Anas cyanoptera).

Next we move to check an established trap. As the researchers climb into the enclosure and crouch against the ceiling, the ducks launch from platforms (provided for trapped ducks to use when they tire of swimming) and dive or dodge to avoid the team’s grasp. Still, they’re fairly calm as Desmond and the others carry them carefully back to shore for analysis. The entire process includes banding, weighing, and measuring the ducks, in addition to identifying their sex and age and swabbing for avian influenza. Each waterfowl receives a small metal band or tag with a unique identifier and code to tell other scientists where this duck was originally captured. Researchers outside the USGS have re-captured ducks that were tagged in Suisun along migration routes that take them out of state. One cinnamon teal from Suisun was tracked across seven states.

collecting Ducks

Researchers use wire mesh to construct traps for collecting waterfowl in Suisun Marsh, CA. (Credit: Erika Sanchez-Chopitea, USGS. Public domain)

At this point in the season, Desmond says, most of the male birds have migrated south and left the females to raise the young. The breeding season has finished — and with it have gone the male mallards’ bold green head feathers. For a layperson, it’s difficult to distinguish the remaining female gadwalls and mallards from one another. It’s not until Desmond, Michael, and Brock retrieve a mix of the two species from a trap that they’re able to confidently show us the subtle differences: warm, rusty red contrasted against streaks of black and white feathers that flash when the gadwall takes flight, and iridescent purple-blue feathers tucked close against the mallard’s body.

The day promises some uncomfortable heat by the time we headquarters employees decide we’ve collected enough photos for one trip. Desmond, Michael, and Brock drop us off at a field bunker and have a quick rest. We have limited experience with the rigors of daily field work and are dehydrated and spent due to an early start, but they appear to be in high spirits as they climb into the truck, say goodbye, and head back into the marsh.

Ultimately, the field crew will take the data back to the lab, record, and analyze it to learn more about which areas of the marsh ducks use during different life stages. State, Federal, and non-profit organizations like the U.S. Fish and Wildlife Service and the California Waterfowl Association will use the study results to identify important waterfowl habitat for restoration or conservation. The findings will also help private individuals who own duck clubs enhance the marsh for migrating waterfowl.

Then there’s the question of avian influenza. Scientists have known that wild waterfowl host strains of the virus for some time, but they’re still learning how drought, water supply management, land use, and other factors affect transmission rates between wild and domestic populations. Swabbing the ducks of Suisun allows WERC researchers to track the virus across the marsh and uncover more of the complex relationships between environment, human activity, and waterfowl that influence its spread.

Following scientists into the field takes big, sweeping ideas and breaks them down into concrete images that can sometimes be easier to access. It’s a treat to be able to see how individuals push projects forward into reality through their daily work. Join us again next time when we join WERC scientists to find out more about research happening in the field.


After being measured and tagged, two ducklings were relased back to Suisun Marsh. (Credit: Erika Sanchez-Chopitea, USGS, Western Ecological Research Center. Public domain.)