Construction of sandbars along the middle Missouri River has provided essential breeding habitat for the Least Tern, an endangered species, and Piping Plover, a threatened species.
This season, most of the birds nesting below Gavins Point Dam are using several sandbars constructed in recent years by the Army Corps of Engineers, said Greg Pavelka, a wildlife biologist with the Corps, and program manager for the tern and plover effort.
“Sandbars have been constructed by the Corps of Engineers to replace sandbars that have been lost to erosion and habitat that has been lost to vegetation encroachment on existing sandbars,” he said. “Without the constructed sandbars there would be only marginal habitat left for the two species below Gavins Point Dam.”
Construction of the most recently completed sandbar complex, at river mile 777.7 above the Vermillion Bridge, was finished just before spring this year. It had a population of around 50 terns and 32 plovers on the most recent survey on June 18th.
Constructed sandbar at river mile 775.0. The view is looking east down the river. Picture taken 23 June 2008. All pictures courtesy of Greg Pavelka, U.S. Army Corps of Engineers. |
Newly constructed sandbar at river mile 777.7. Picture taken 23 June 2008. |
A constructed sandbar complex fifteen miles west of Gavins Point Dam on Lewis and Clark Lake was re-engineered, and just completed this spring. It is now home to about 200 terns and 50 plovers.
Currently, the 2008 Adult Census is being conducted by the Corps on the Missouri River from Fort Peck Lake in eastern Montana down to Ponca State Park in northeastern Nebraska. About 800 miles of the river are censused during this time.
In 2007, a record 1,010 adult least terns and 1,251 adult piping plovers were counted on the Missouri, according to Pavelka.
This season, for the stretch of the Missouri River below the dam, the constructed sandbars had 94 Piping Plover nests, with 45 at other locales during the mid-June survey. For Least Terns, there were 96 nests at the constructed sandbars, and ten elsewhere, according to the census details.
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Least Tern and Piping Plover Nesting Details Results of survey conducted on 18 June 2008. The nesting information is color coded by construction date with the sandbars constructed in 2004 and 2005 color coded red while the new sandbars that were constructed in the fall of 2007 and the spring of 2008 color coded in blue. Information courtesy of the Army Corps of Engineers. Piping Plover Nesting – Missouri River below Gavins Point Dam
Least Tern Nesting – Missouri River below Gavins Point Dam
Piping Plover Nesting – Lewis & Clark Lake
Least Tern Nesting – Lewis & Clark Lake
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“Both species prefer sandbars located in midstream, with a sand and gravel mix, enough elevation to prevent the loss of nests from flooding and vegetation cover of less than 15%,” Pavelka said. “Piping plovers also require large areas of wet sand so that they can forage for worms, fly larvae, beetles, crustaceans, mollusks, and other invertebrates. Least terns need shallow water backwaters where they will dive after their primary food source – fish.”
Recent heavy rains in the river basin have caused the loss of some bird nests thus far season, including several below Gavins Point Dam. Upriver, high tributary inflows from the rains have caused Lake Oahe to rise. Lake Sakakawea in North Dakota has also risen as it captures the snowpack runoff from the northern Rocky Mountains. The higher water levels in the reservoirs have inundated shoreline habitat used by the plovers. Where possible, Corps staff have moved the nests to higher ground, but in several cases, nests have been flooded.
Bird Surveys
A crew comprised of four Army Corps of Engineer employees, and one from the South Dakota Game and Parks monitor both species during the breeding season along the Missouri National Recreation River. The group visits each nesting locale about once a week.
Access restriction sign used to protect breeding areas used by the terns and plovers. |
Access restriction sign on sandbar at river mile 777.7. |
Monitoring begins in mid-April as the piping plovers arrive from their wintering grounds along the Atlantic and Gulf Coasts and Caribbean Islands. Least terns make their appearance about a month later, arriving on the Missouri around mid-May.
The crew uses a handheld computer with a global positioning system unit to precisely map nest locations and to record nest data, chick numbers and ages and habitat status, Pavelka said. At the end of the day the data is uploaded via the Internet to the Missouri River Recovery Least Tern and Piping Plover Data Management System (TPDMS). There the data is analyzed and used to make decisions on water releases out of the dams. Least Tern and Piping Plover data summaries for 2008 and previous years are available to the public at the TPDMS website.
In addition to the monitoring done by the Corps of Engineers, the Corps is funding two research projects on the Missouri River.
Study blind used for research on terns and plovers. Picture taken in 2007. |
The U.S. Geological Survey is in its third year, and final year, of investigating the foraging ecology of the Least Tern on the constructed sandbars.
The Virginia Polytechnic Institute is continuing to study how Piping Plovers use the constructed sandbars. A three-year PhD dissertation project was recently completed, while a two-year Master’s degree was started this season.
Monitoring will continue until the end of August when the last of the chicks have fledged and the birds depart for the wintering grounds.
Information is also being kept on birds that occur elsewhere in Nebraska.
Terns and Plovers that use the Niobrara River are monitored by staff with the National Park Service. The nests on the Niobrara were washed away by heavy rains in early June, but birds are re-nesting on the river, according to information received by Pavelka.
Tern and Plover nesting along the Platte River and lower Loup River is monitored by the Tern and Plover Conservation Partnership. A summary of the number of birds noted in different counties within their breeding range is being updated at the end of each month, through September.
Mandate to Protect
A biological opinion issued by the Fish and Wildlife Service provides the mandate for conservation of endangered and threatened species along the Missouri River.
The opinion, issued in 2000 and amended in 2003, found that the six dams built in past decades along the Missouri River, as well as changes in the river channel to provide waterway navigation have a dramatic impact on the tern and plover, as well as the pallid sturgeon.
Since the actions of the Corps, as operator of the dams and being responsible for maintenance of the river channel, affects these species, they were required to monitor the species and undertake efforts to ensure their survival.
Federal monitoring efforts have been underway since 1986, with the Corps taking over all monitoring along the Missouri River in 1993. The Nebraska Game and Parks Commission carried out population surveys in prior years.
The 1990 recovery plan for the interior population of the Least Tern set a goal of having a stable population of 900 along the Missouri River.
The Missouri River is home for the greatest number of the northern Great Plains population of Least Terns. The number of birds has fluctuated between 800 and 1000 in the past three years, Pavelka said.
The 1988 recovery plan for the Northern Great Plains Population of Piping Plovers set a recovery goal of 425 adult pairs, or at least 850 birds. In 1,251 adult plovers were counted along the Missouri River, according to Corps’ information.
The Missouri River is important to the recovery of the northern Great Plains population with about one-fourth of the Great Plains Piping Plovers occurring along the river.
Boom and Bust
“There have been a lot of ups and downs” during the years, said Pavelka, who has been working with the tern and plover project since 1993. “The terns and plovers are adapted to a boom and bust cycle. It’s all about water … too much or too little.”
High flows and drought conditions cause differing conditions along the river and at the reservoirs.
“One year, high water levels will inundate most of the habitat leaving little area for the birds to nest,” he said. “The next season may bring low water levels and abundant habitat and the birds will be more successful.
Aerial view of the channel location where a sandbar was constructed at river mile 777.7. |
“In 1997 high releases out of Gavins Point Dam inundated most of the sandbars, but in 1998 low releases exposed many new sandbars that were devoid of vegetation. High nest success and fledging success continued for several years as the birds used the new sandbars. Drought conditions meant lower lake levels and more beach habitat on Lake Oahe and on Lake Sakakawea for Piping Plovers to successfully raise broods.”
The monitoring program is vital for monitoring the populations to ensure their survival, Pavelka said. “The Corps of Engineers has a tremendous commitment to ensure the survival of these two species.”
“The construction of new sandbars will continue in coming years on the Missouri below Gavins Point Dam, on Lewis and Clark Lake and on the Missouri below Fort Randall Dam. It is important to provide sandbar habitat at various locations along the river in order to spread out the birds. Though the constructed sandbars have been successful in attracting terns and plovers, it makes the birds, their nests and chicks susceptible to a roving predator or a passing thunderstorm. By ensuring that there is enough habitat for the birds, the Corps is committed that there will be least terns and piping plovers on the Missouri River for years to come.”
Least Tern and Piping Plover Data Management System with regular updates by the Army Corps of Engineers, during the breeding season
