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Banding to shed light on mottled ducks

July 14, 2018

One evening last week, as dusk yielded to the profound darkness that on moonless summer nights still envelops wildlands far enough removed from the civilization’s halo of artificial light, scattered clusters of mottled ducks — mostly hens shepherding their almost-grown ducklings — paddled into the flooded bulrush and other aquatic vegetation fringing open water of an expanse of shallow coastal wetlands on the upper Texas coast’s Anahuac National Wildlife Refuge, settling in for the night.

It would not be a quiet night for many of them. Some would be chased and snatched from their home, fit with bands on their legs and maybe have a bit of their blood drawn. But, in the end, they would be delivered, unharmed, back to their world.

That world is almost wholly limited to the coastal plain of the western Gulf Coast, specifically the remaining marsh and coastal prairie wetlands found in a 50- to 100-mile-wide band of country stretching from Mobile Bay, Ala., to Tampico, Mexico.

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Stay-at-home bodies

Unlike almost all other waterfowl — even the black-bellied and fulvous whistling ducks and wood ducks that nest in Texas — mottled ducks don’t migrate. They may shift laterally up and down the coast, flying a hundred miles or so to take advantage of better habitat conditions or food supplies. But they don’t go south for the winter or north in the spring. They are homebodies; almost 90 percent of the world’s mottled ducks are born, live and die in that narrow band of the Gulf Coast coastal plain.

As such, the fate of these Gulf Coast natives is inexorably tied to the health of their homeland. That homeland isn’t what it once was, and neither is the population of these large, dusky ducks.

Texas’ mottled duck population has been in a slow, steady decline over the last several decades. Midwinter surveys in the early 1970s counted three times as many mottled ducks in Texas as were counted in recent midwinter surveys.

Louisiana’s mottled ducks haven’t seen that kind of decline, and their population has been stable or maybe slightly increasing. Combined, the western Gulf Coast population of mottled ducks is stable or only slightly declining.

There are still a lot of them. A 2016 survey estimated the breeding population of mottled ducks in Texas and Louisiana at about 136,000. But there are concerns about the birds’ future, especially with the continuing land use and environmental changes on the coastal plain — changes that have shrunk mottled ducks’ world.

Waterfowl managers have long been engaged in efforts to monitor mottled duck numbers and learn more about the life history, population dynamics, habitat requirements and preferences, movements and other information needed to make wise decisions that benefit these endemic, iconic coastal waterfowl.

That’s why, as mottled ducks settled in for the dark night, a group of waterfowl biologists and technicians gathered on the edge of that particular expanse of coastal wetlands on Anahuac NWR.

In the gloaming, some slid an airboat off a trailer and into shallow water and loaded it with plastic crates and spotlights and other gear. Others fashioned a small work area with boxes of tools and other necessities, an ice chest or two that would double as seats and tables, a set of lights and a generator to produce the electricity to run them. All occasionally waved absentmindedly at the legions of mosquitoes and deer flies swarming in the heavy, hot air.

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Agencies team up

The group is part of a cooperative effort among the U.S. Fish and Wildlife Service, Texas Parks and Wildlife Department, Louisiana Department of Wildlife and Fisheries, Gulf Coast Joint Venture bird conservation partnership and Ducks Unlimited, the nation’s premier private waterfowl/wetlands conservation organization, to learn more about mottled ducks and put that knowledge to work to improve the lot of the wildfowl.

This night, the crew — a combination of TPWD staff based at the agency’s J.D. Murphree Wildlife Management Area and USFWS staff from the Texas Chenier Plain National Wildlife Refuge Complex — were continuing a long-running program aimed at catching and placing individually numbered metal leg bands on mottled ducks in Texas and Louisiana.

The project, which for almost two decades annually has banded as many as 5,000 mottled ducks, has yielded considerable insight into annual survival and movements of the birds. The information, garnered when waterfowlers who take a banded bird report the data through an online system, has proved vital to management decisions.

The banding effort is concentrated during July and August, months when mottled ducks hatched this year are old enough and large enough to be banded but still haven’t developed flight feathers and are unable to fly. Also, July through mid-September is when adult mottled ducks molt, shedding their primary flight feathers and growing new ones; they are flightless for about four weeks.

During this period, the birds tend to concentrate in large, shallow, fresh or brackish wetlands that offer a matrix of open water and vegetation, providing the vulnerable birds with food and cover.

Taking advantage of the birds’ flightless period and focusing their efforts on dark nights around the new moon, banding crews using airboats and spotlights can search these shallow wetlands, swoop down on the flightless birds, capture them and place them in holding crates for transport to a work area where they are banded, their age and sex and band number recorded and then released.

This year, some mottled duck banders in Texas and Louisiana have added a new project to the annual summer mottled duck banding effort, this one aimed at using modern technology to help answer nagging questions about the nesting proclivity of mottled duck hens.

Nesting propensity — the proportion of hens that nest and lay at least one egg — and nesting success are two of the most important factors that determine recruitment of young mottled ducks. Nesting propensity is one of the least-known pieces of the puzzle, said Jena Moon, a USFWS biologist for the upper Gulf Coast Zone.

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Geolocators aid study

To try answering that question, biologists this year are starting a research project that aims to fit about 240 hen mottled ducks in Louisiana and Texas with leg bands that hold a miniature light-level electronic geolocator unit. The tiny geolocators record data on the duration and timing of daylight as a means of calculating geographic location.

But that data, biologists have learned, also can be used to determine nesting activity. When a hen sits on a nest for a long period of time — to lay or incubate eggs — the geolocator on a leg band is obscured from sunlight, and records that period as darkness. Such anomalies — the geolocator recording darkness during daylight hours — indicates that the hen was on a nest. Such information could go a long way in helping biologists understand nesting propensity of mottled ducks, Moon said.

Moon is one of the group of waterfowl scientists that developed the research project to fit mottled duck hens with geolocator bands.

The geolocators, which have a two-year-or-more lifespan, are attached to a plastic band fit to the leg of hen mottled ducks. The birds also are fit with a traditional metal leg band on the opposite leg. The band holding the small geolocator includes contact information that waterfowl hunters who take one of the marked birds can use to alert researchers. Researchers will download the data from the geolocator; the hunter gets to keep the band.

If banding crews recapture one of hens fit with a geolocator in coming years, they can remove the device and download the data.

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Testing blood for lead

If results from the initial geolocator banding proves successful — if hunters report taking birds with bands and allow researchers to retrieve he data and those data provide useful information — the program could be expanded and extended.

On the night last week, Moon, TPWD waterfowl biologist Steven McDowell and the crew of USFWS and TPWD staffers placed a handful of geolocator bands on hen mottled ducks and leg bands on all of the many other mottled ducks captured during the nocturnal sorties.

McDowell also took blood samples from some of the ducks, part of an ongoing study to monitor lead levels in the birds. Mottled ducks have proven to be one of the most prone waterfowl species to have higher than normal lead levels — a problem associated with the birds continuing to ingest spent lead shot deposited in wetlands before non-toxic shot was mandated for all waterfowl hunting more than two decades ago. Those elevated lead levels can have detrimental effects on the bird’s health and reproductive ability.

It was a long, hot, wet, muddy session that ended long after midnight, but one that saw the banding crew collect more than enough of the birds to make the effort worthwhile.

The ducks they captured, recorded, banded and released back into the pitch-black darkness of the coastal marsh carry with them the ability to provide illumination that could brighten the future of these signature, endemic Gulf Coast waterfowl.

shannon.tompkins@chron.com

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