25 August 2009

Severe July Weather Reduces Tern and Plover Success on MNRR

A severe weather event on July 8, 2009 had a significant detrimental impact on breeding Least Tern and Piping Plover, as the storm went eastward down the Missouri National Recreation River in northeast Nebraska.

"The storm hit some of our constructed sandbars pretty hard," said Greg Pavelka, a wildlife biologist with the Army Corps of Engineers, and program manager for their tern and plover effort.

The constructed sandbars were recently created below Gavins Point dam, and provide essential breeding habitat for the tern - an endangered species - and the plover - a threatened species.

"Three of our five major sandbars saw substantial reductions in the number of chicks counted by our survey crew before and after July 8," Pavelka said. The following differences at several sandbars are based on the findings of regular surveys throughout the breeding season:

* River Mile (RM) - 791.5 the number of chicks went from 37 to 7
* RM 775.0 - from 41 to 22
* RM 774.0 - from 88 to 30.
* RM 795.5 - there was a small decrease from 55 to 48 and
* RM 777.7 - was an increase in chicks from 38 to 45 before and after July 8.

"Weather was also the leading cause of nest losses for both species below Gavins Point with 29 of 67 plover nests that failed being due to weather and 15 of 25 tern nest losses."

Archived weather reports for the severe weather indicate the extent of winds and size of hail for reporting stations in the immediate vicinity of the river.

Details from the interactive Local Storm Report Viewer, provided by the National Oceanic and Atmospheric Administration give particulars. Information given here is:

Location from Nearest Locality, County, State ~ Latitude-Longitude; Weather event (Reporting station)
* 1 SE ST. HELENA, CEDAR, NE ~ 4280 – 9724; 40 TO 50 MPH WINDS ALSO. (OAX)

Further reports, provide additional weather details for the July 8th storm, with reports from several different times, as archived by the Iowa Environmental Mesonet, provided by the Iowa State University Department of Agronomy.

Location, County, State – weather event and notes
* Cedar, St. Helena, NE - TSTM WND DMG, extensive crop damage due to winds and hail from St. Helena to Wynot to Obert.
* Cedar, 1 Se St. Helena, NE – HAIL, 1.75, 40 to 50 mph winds also.
* Cedar, Wynot, NE - TSTM WND DMG, crops damaged in the Wynot area due to hail and wind. Time estimated.
* Cedar, Wynot, NE – HAIL  1.75
* Knox, Crofton,NE – HAIL  1
* 13:05 GMT: Cedar, Hartington, NE - TSTM WND GST 62, according to local cable tv weather instrument ... time estimated.  Rainfall of 2.16 inches also.
* 13:13: Cedar, Hartington, NE – HAIL, 0.88
* 14:00 Cedar, Wynot, NE - HEAVY RAIN 3.55, storm total through 9 am ... water reported over county roads near town.

Severe weather reports from the Omaha office of the National Weather Service.

Severe weather reports from the Sioux Falls office of the National Weather Service.

Radar view of the severe weather on July 9, 2009. Image from the Sioux Falls office of the National Weather Service.

"Despite the losses, it was not a catastrophic year below Gavins Point," Pavelka said. "Productivity was close to the goals set forth in the U.S. Fish & Wildlife Service's biological opinion for the Missouri River. The Service set a fledge ratio goal of 1.22 fledglings per adult pair for the plovers and 0.94 for the terns. Below Gavins Point the fledge ratio in 2009 was 1.09 for the plovers and 0.95 for the terns. In 2009 below Gavins Point there were 239 plover adults, 130 plover fledglings, 220 tern adults and 105 tern fledglings."

Nests of the Piping Plover and Least Tern on the upper Missouri River. Information courtesy of the Missouri River Recovery Least Tern and Piping Plover Data Management System, maintained by the Army Corps of Engineers.
Piping Plover 2009
SegmentTotal NestsSuccessful Nests
Fort Peck Reservoir61
Fort Peck River00
Lake Sakakawea7511
Garrison River16684
Lake Oahe 96 28
Lake Francis Case00
Fort Randall River105
Lewis and Clark Lake8055
Gavins Point River17088
Region Subtotals
Missouri River603272
Interior Least Tern 2009
Fort Peck Reservoir 00
Fort Peck River3324
Lake Sakakawea2211
Garrison River8843
Lake Oahe7539
Lake Francis Case 10
Fort Randall River 135
Lewis and Clark Lake 15993
Gavins Point River 12393
Region Subtotals
Missouri River514308

The overall impact of the severe storm event depends on the scale being considered, Pavelka said.

"For the 59 mile section of the Missouri River from Gavins Point Dam to the channelized river, no matter how spread out the habitat is along this section, a major storm will wreak havoc on the nesting birds. In the context of the entire Missouri River, least terns nest on parts of the Missouri below Fort Peck Dam in Montana, Garrison Dam in North Dakota and Fort Randall Dam in South Dakota and the terns nest on major tributaries such as the Platte and Niobrara Rivers in Nebraska. The plovers likewise nest along the same sites and also utilize beaches on Lake Sakakawea and Lake Oahe. If you look at a region wide basis, the least terns nest on the lower Mississippi, Red, Arkansas Rivers and their tributaries. The piping plovers also use the alkali lakes of North Dakota and Montana and habitat in the Canadian provinces of Alberta, Saskatchewan and Manitoba. Obviously the greater the range the less vulnerable a species is to weather events.

"Both species also have strategies to counter losses due to weather events and predation. Both will re-nest early in the breeding season if they lose a nest or a young brood. Also, both are considered ‘boom and bust’ species whereby they can make up for a year of low productivity with high productivity in the following year. Of course, too many bad years and too few good years can cause a species to spiral down towards extinction.

"Where the birds nest below Gavins Point Dam is highly modified, both in the lack of habitat and the lack of a natural process (spring flooding from snowpack runoff) to restore habitat," Pavelka said in an email. "The Corps' solution to artificially construct habitat has provided nesting and brooding areas for the two species. However, the birds' preference for this constructed habitat has lead to a concentration of adults, nests and chicks that leave them vulnerable to weather events, predation and density dependency issues among the birds. It also has caused the birds to not use habitat that is marginal, but has been used in the past before the constructed sandbars were built. The solution would be to continue to construct sandbars and to rehabilitate existing sandbars that have become marginalized."

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