Brussels, Ill. - Biologists at Two Rivers National Wildlife Refuge have
determined that the summer drawdown performed on Swan Lake was an
overwhelming success based on exceptional amounts of natural seed
production by wetland plants and high levels of bird use during the early
part of the 2012 fall waterfowl migration.

The backwaters of the Illinois River that make up Swan Lake are an
important migration stop along the Mississippi flyway. Located near
Grafton, Ill., the lake is managed by Two Rivers National Wildlife Refuge
part of the U.S. Fish and Wildlife Service (FWS).

FWS biologists Ken Dalrymple and Brian Loges and researchers from the
University of Tennessee report that seed production by plants grown in Swan
Lake averaged more than 3,000 pounds per acre, which is an unprecedented
amount of natural food for waterfowl. Typically native moist-soil plants
growing in wetlands similar to Swan Lake produce less than half of the
production reported from this summer’s growing season.

The report states 164,120 ducks could use Swan Lake for 110 days based on
available seed.

“Most refuges cannot sustain this number of birds without providing
supplemental corn” stated Matthew Gray, Ph.D. from the University of
Tennessee. “In other words, the drawdown of lower Swan Lake will
provide significant quality habitat for migrating waterfowl this winter!”

A drawdown is a wetland management technique performed by slowly removing
water from a wetland for the summer season to dry out the sediment at the
bottom and promote plant growth. The ability of the refuge staff to
complete a drawdown on the lower half of Swan Lake was enhanced by this
summer’s drought. A drawdown could not be completed in recent years due to
extended flooding on the Illinois River.

In addition to waterfowl, many other bird groups benefit from the flush of
vegetation and insects following the drawdown.

“Estimating and then monitoring the number of waterfowl that can be
supported in the lake are useful exercises to measure success towards the
refuge’s waterfowl habitat goals,” said Brian Loges, FWS Regional Zone
Biologist. “Refuge management centers on evaluating how the resources of
the refuge can help support the needs of migrating waterfowl.”

From weekly aerial counts the Illinois Natural History Survey has reported
on average 108,000 ducks for the past three weeks on Swan Lake while ground
survey estimates have been routinely higher. The aerial counts are
performed by flying over a number of waterfowl survey areas. View these
counts and others online by following the link at:
http://www.fws.gov/refuge/Two_Rivers/seasons_of_wildlife/index.html.

“Other factors such as ice and water levels can influence bird abundance on
the lake but an adequate food supply in Swan Lake should not be a limiting
factor for the remainder of the fall migration,” said Loges.

For more information, call the refuge at 618-883-2524.

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