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Scientists Track Pintail-Duck Migration to Learn More About the Species' Population Decline

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Pintail duck fitted with a standard radio transmitter
Ready for tracking: Pintail duck fitted with a standard radio transmitter. Photograph courtesy of Gary Zahm, U.S. Fish and Wildlife Service. [larger version]
On September 29, pintail 17530's backpack transmitter beamed a signal from the southwest coast of Alaska to a satellite. She was flying south, nearly 10 months after USGS scientists had equipped her with a platform transmitter terminal (PTT) last winter in California's Central Valley, where nearly half of North America's pintail ducks winter.

Back in Dixon, CA, waterfowl biologists at the U.S. Geological Survey (USGS) have followed pintail 17530's travels on an interactive computer map. Her route appears as a series of red dots linked by directional arrows. One map each documents the migratory route of 30 female pintail ducks that left the valley wearing PTTs in mid-February, northbound for nesting grounds.

"The pintails we have tracked over the past 3 years by satellite migrate many hundreds of miles along the Pacific flyway to nesting destinations ranging from the prairies of southern Alberta and Saskatchewan to Alaska, and even Russia," said wildlife biologist Michael Miller of the USGS' Western Ecological Research Center.

An international team of waterfowl biologists and technicians from the USGS, Ducks Unlimited, Inc. (DU), DU Canada, and the California Waterfowl Association (CWA), funded primarily by the Tuscany Research Institute of Las Vegas, NV, is using satellite telemetry to determine the migration routes and identify the major resting areas of these birds. Miller leads this research effort, assisted by Joe Fleskes and several other USGS biologists and geographic-information-system (GIS) technicians in the everyday running of the study. By piecing together what they learn from this study with additional data from studies using standard radio telemetry, the scientists hope to determine whether unknown factors are affecting this species' decline.

Map of western north America showing migration route of pintail 17530
Above: Migration route of pintail 17530. Star in California's northern Central Valley shows where she was tagged with a satellite transmitter. Dots show Julian dates (number of days elapsed since Jan. 1, 2002) on which the bird was present. Julian date 272, for example, corresponds to September 29.
Below: Cumulative locations through October 1, 2002, of migrating pintails tagged in late winter 2001 for satellite tracking. Red dots, pintails tagged in California; green dots, pintails tagged in New Mexico; yellow dots, pintails tagged in Texas. The red dots approximately delineate the Pacific flyway; the green and yellow dots, the central flyway. Updates and additional maps of pintail locations can be viewed on the "Discovery for Recovery Web site.
map of western North America showing cumulative locations through October 1, 2002, of migrating pintails tagged in late winter 2001 for satellite tracking
"Persistent drought, large populations of alien predators, and conversion of native prairie to farming in critical nesting regions of southern Canada and the northern Great Plains in the United States have resulted in repeated pintail nest failures over many decades," said Fleskes.

As recently as the 1970s, the U.S. Fish and Wildlife Service estimated a North American breeding population of 5 to 7 million pintails in principal nesting areas. By 1991 and again in 2002, however, the pintail breeding population dipped to an all-time low of 1.8 million.

One of the most widely distributed ducks in the world, the northern pintail (Anas acuta) is a medium-size duck with slender, elegant body lines. Pintails are "dabbling ducks" and forage on grains, marsh-plant seeds, and aquatic invertebrates throughout the fall and winter.

"During the non-nesting seasons, pintails must replenish their body reserves to be able to survive winter, migrate north again the following spring, and produce young," said Fleskes.

Until the 1980s, said Fleskes, midwinter populations of pintails in California's Central Valley reflected the overall population trend. Since then, however, declines have been greater in the southern regions of the Central Valley (San Joaquin Valley) than in northern areas (Sacramento Valley). To understand this disproportionate decline, Fleskes has worked with Dave Gilmer, also a USGS research biologist, and Robert Jarvis, from Oregon State University, to fit standard radio transmitters to the backs of 419 young and adult female pintails and follow them for three consecutive winters.

The three scientists found that neither contaminants nor disease, but a redistribution accounted for the disproportionate declines in wintering pintails in the southern Central Valley.

"More than 80 percent of the tagged pintails shifted each midwinter from areas in the south having less abundant habitat for food and refuge, to locales in the Sacramento Valley more favorable for their survival," said Fleskes.

The change each winter in pintail distribution appears to be related to loss of suitable habitat, drought conditions, and the lesser-quality habitat of cotton-farmed lands in the San Joaquin Valley, which lack winter flooding, in contrast to the flooded ricelands of the Sacramento Valley, said Fleskes.

Spring migration to nesting regions begins as early as February and is well underway by March. Pintails begin to arrive in prairie nesting areas at the end of March or early April. By May, females will be incubating their eggs in nests they have built on the ground of short grasses and brush. They lead their 8 to 12 ducklings, which hatch together in one day, to water. There the ducklings feed on mostly aquatic invertebrates till fledging by July or August.

For the spring 2003 migration, the team of scientists will outfit 30 adult female pintails with PTTs in the Sacramento Valley. As they did last winter, the team will tag an additional 10 birds in central New Mexico and 20 in Texas, to add birds to the study that winter in the central flyway. After trapping crews release the birds, Miller will receive satellite data on each bird's movements every 3 days through the following August, or until the PTTs quit.

"The first stop or staging area for more than 75 percent of the pintails is northeastern California and southern Oregon, where they build body reserves for their remaining migration," said Miller. "They remain there for as little as a few days up to two months, depending on the migration routes ultimately used."

Truck with antennae used for tracking ducks tagged with standard radio transmitters
Radio tracking: Truck with antennae used for tracking ducks tagged with standard radio transmitters. Mountains in background are the Sutter Buttes in California's Sacramento Valley, after a rare snowfall. Photograph by Michael Miller, USGS.
The team pinpoints specific habitats the ducks use at this staging area by fitting additional ducks with standard radio transmitters and following them from the ground. Obtaining day and night locations for each duck in spring 2002, the researchers determined specific habitat use for more than 80 percent of 150 radio-tagged pintails.

"The satellite and standard radio data have revealed key staging areas in northern California and southern Oregon," said Fritz Reid, DU's director of conservation planning for the western United States. "Organizations such as Ducks Unlimited and the U.S. Fish and Wildlife Service can now focus protection and restoration efforts on these areas with the aid of private landowners and state agencies. The pintail satellite data have further provided insight into critical areas of the prairies and western boreal forest that warrant protection," Reid added.

Upon leaving southern Oregon and northeastern California, about 40 percent of the pintails fly directly to southern Canada, followed by an additional 25 percent that use one or more additional resting areas along the way, said Miller. Another 25 percent head for Alaska, traveling along the coast or directly over the Pacific Ocean, a trip of more than 2,000 miles. The remaining 10 percent fly to the Dakotas.

Miller directed field technicians to nearly 100 stopover areas to document habitat use and behavior of pintails during the first 2 years of the project. "Pintails observed near the tagged hens used a variety of habitats, ranging from stock ponds to tundra," said Miller, "with greater use of private than public lands."

One of the principal pintail nesting regions is the Prairie Pothole Region in North and South Dakota, northeastern Montana, and the southern prairie provinces of Canada. "Prairie drought has prevailed each year of the study period, and most of the satellite-tracked pintails flew on to areas farther north," said Miller. The birds migrating directly to Alaska, however, another critical nesting region, were not affected by prairie drought.

Above-average rainfall in southern Alberta and southern Saskatchewan this summer after the pintails' passage gives Miller and the team cause to believe they may find pintails nesting there next spring. "If the wetlands are replenished and uplands have enough cover to attract pintail females next March and April, we can expect a high proportion of tagged pintails to stop in the prairie region, rather than continue on farther north."

To learn more, please visit the "Discovery for Recovery" Web site.

Related Sound Waves Stories
Teamwork Sheds Light on Shorebird-Migration Mysteries
May 2002

Related Web Sites
Discovery for Recovery - Tracking Pintail Duck Migration
U.S. Geological Survey (USGS)
Ducks Unlimited
non-profit conservation organization
Pintail Program
California Waterfowl Association (CWA)
Tuscany Research Institute
non-profit organization

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in this issue: Fieldwork cover story:
Seagrass Restoration in Tampa Bay

Tracking Pintail-Duck Population Decline

Remote Sensing of Coral Reefs at Biscayne National Park

Exploring the Puerto Rico Trench

Research Assateague Island Restoration

Outreach Dedication of New Lake Mead Research Vessel

Meetings Sea-Level Change Workshop

The Need for Better Scientific Understanding of Sea-Level Change

Remote-Sensing at Cape Cod National Seashore

Familiar Faces at Fall Meetings

Giving Interns a View of Science Career Paths

Staff & Center News Visiting Engineer Brings Modeling Expertise

Parsons Succeeds Lee as Acting Chief Scientist for WRCMG Team

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