Bryan Reiley, a graduate research assistant at the Illinois
Natural History Survey, studied the body condition and number of
male warblers returning to two sites in southeast Arkansas
during four breeding seasons. He investigated the warblers
before the 2008 catastrophic flooding of the Mississippi River
and three years after the flood.
Swainson’s Warblers (Limnothlypis swainsonii) are rare,
occurring in the Caribbean basin during the winter months and
primarily in the southeastern United States from April through
August. They also reach southern Illinois and the Appalachian
Mountains. This species typically lives in canebrakes adjacent
to rivers in floodplain forests.
From 2005 to 2010, Reiley studied 278 males. He anticipated that
their body condition would decrease in the years after the 2008
flood because warblers forage for insects under fallen leaves
and debris. He also assumed that fewer birds would return to the
previously flooded site in subsequent years.
He found that the condition of males was actually better in the
years after the flood, perhaps because the La Niña climate
pattern created favorable conditions at the birds’ wintering
Flooding did affect the number of males returning to the study
site, however. Before the flood, 20 to 31 males returned to
breed each spring, whereas in 2008, 18 males returned. The
following year, Reiley counted only 7 birds, and in a follow-up
observation in 2014, only 2 warblers were observed at the site.
For birds that attempted to breed in these habitats in the years
following the flood, reduced leaf litter and shrub cover might
have resulted in reduced habitat quality and decreased nesting
success, leading to a significant drop in the number of birds
occupying the area in the second and third years post-flood.
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“Habitats are never static,” Reiley said. “Swainson’s Warblers may
reside in upland habitats following a significant flood. I’ve seen
them feeding in the trees when they would normally forage on the
ground. They can be flexible when their habitat is continually
To keep Swainson’s Warblers in a forest environment after a flood,
increased forest management may be necessary, Reiley said. Flooding
is not a unique condition, but the increased frequency and duration
of flooding that may result from a changing climate can be stressful
“If the habitat changes too much, Swainson’s Warblers will not use
it, and they may never return to that area,” Reiley said.
The study was funded by the U.S. Fish and Wildlife Service. Reiley
is a PhD candidate in the Department of Natural Resources &
Environmental Sciences, and his advisor is Thomas Benson, a wildlife
ecologist in the Prairie Research Institute’s Illinois Natural
History Survey. The article can be found at
[Lisa A. Sheppard]