[wisb] Re: Study shows earthworms to blame for decline of ovenbirds in northern Midwest forests
- From: "Richard L. Smallwood-Roberts" <warbugs.smallwood@xxxxxxxxx>
- To: calocitta8@xxxxxxxxx
- Date: Tue, 6 Mar 2012 15:05:02 -0600
Thanks for the heads-up on the issue. There were no lack of Ovenbirds
in Price County South of Phillips back in 2003 at my research site. I
will make an effort to reevaluate the population this spring and try
to determine if there is any noticable decline and get back to you
with my observations.
On 3/1/12, Jesse Ellis <calocitta8@xxxxxxxxx> wrote:
> Folks, if you fish, don't dump your worms.
> On Thu, Mar 1, 2012 at 8:37 AM, Anne Moretti <amoretti@xxxxxxxxx> wrote:
>
>> An interesting and disturbing study about the effect of non-native
>> earthworms in northern forests and their effect on nesting Ovenbirds. Has
>> anyone noticed a decline of Ovenbirds in the areas mentioned?
>>
>>
>> Anne Moretti
>>
>> Dousman
>>
>> Waukesha Co.
>>
>>
>> Subject: Study shows earthworms to blame for decline of ovenbirds in
>> northern Midwest forests
>>
>> http://www.eurekalert.org/pub_releases/2012-02/s-sse022912.php
>>
>>
>>
>> 29-Feb-2012
>>
>>
>>
>> Study shows earthworms to blame for decline of ovenbirds in northern
>> Midwest
>> forests
>>
>> A recent decline in ovenbirds (Seiurus aurocapilla), a ground-nesting
>> migratory songbird, in forests in the northern Midwest United States is
>> being linked by scientists to a seemingly unlikely culprit: earthworms.
>>
>>
>>
>> A new survey conducted in Minnesota's Chippewa National Forest and
>> Wisconsin's Chequamegon-Nicolet National Forest by a research team led by
>> Scott Loss of the University of Minnesota and the Smithsonian Migratory
>> Bird
>> Center has revealed a direct link between the presence of invasive
>> European
>> earthworms (Lumbricus spp.) and reduced numbers of ovenbirds in mixed
>> sugar
>> maple and basswood forests.
>>
>>
>>
>> The results are detailed in a paper published online in the scientific
>> journal, Landscape Ecology.
>>
>>
>>
>> European earthworms are invading previously earthworm-free hardwood
>> forests
>> in North America the scientists say, and consuming the rich layer of leaf
>> litter on the forest floor. In turn, herbaceous plants that thrive in
>> thick
>> leaf litter and provide cover for ground-nesting birds are thinning out,
>> replaced by grasses and sedges.
>>
>>
>>
>> As a result, ovenbird nests are more visible and vulnerable to predators
>> and
>> ovenbirds searching for nesting sites reject these low-cover areas
>> outright.
>> Areas of reduced leaf litter also contain fewer bugs for the ovenbirds to
>> eat, requiring them to establish larger territories, resulting in fewer
>> birds over a given area.
>>
>>
>>
>> The worms invading northern Midwestern forests (and forests in the
>> northeastern U.S. and Canada) have been in the U.S. since soon after the
>> first European settlers arrived. Loss explains the worms were brought over
>> inadvertently in the ballast of ships, in the root balls of agricultural
>> plants or on purpose for use in gardening. Only now is the leading edge of
>> their continued invasion, caused mainly by logging activities and
>> fishermen
>> dumping their bait, reaching interior wilderness areas such as parts of
>> the
>> study site in the remote forests of Wisconsin and Minnesota.
>>
>>
>>
>> "Night crawlers [Lumbricus terrestris] and the slightly smaller red worms
>> [also called leaf worms or beaver tails, Lumbricus rubellus], have the
>> most
>> damaging impacts to the soil, litter layer, and plants in forests that
>> were
>> historically earthworm-free," Loss says.
>>
>>
>>
>> "Everyone has probably heard at one time or another that earthworms have
>> really positive effects in breaking down soil and making it more porous,"
>> Loss explains. "This is true in agricultural and garden settings but not
>> in
>> forests in the Midwest which have developed decomposition systems without
>> earth worms."
>>
>>
>>
>> Because the forested areas of the Midwest U.S. were once covered in
>> glaciers, there are no native earthworm species present in the soil.
>> "These
>> earthworm-free forests developed a slow fungus-based decomposition process
>> characterized by a deep organic litter layer on the forest floor," Loss
>> says.
>>
>>
>>
>> Earthworms feed on this layer of leaf litter and make it decompose much
>> faster, Loss explains. "As a result, we see the loss of sensitive
>> forest-floor species such as trillium, Solomons seal, sarsaparilla and
>> sugar
>> maple seedlings and a shift in dominance to disturbance-adapted species
>> like
>> Pennsylvania sedge."
>>
>>
>>
>> One result is reduced nest concealment for the ovenbird and increased
>> predation by squirrel and bird predators.
>>
>> The researchers found no decline in three other species of ground-nesting
>> birds included in their survey-the hermit thrush (Catharus guttatus),
>> black-and-white warbler (Mniotilta varia) and veery (Catharus
>> fuscescens)-nor did they find a correlation between ovenbird decline and
>> invasive worms in other forest types, such as red oak, paper birch and
>> aspen.
>>
>>
>>
>> "Our results suggest that ovenbird density may decline by as much as 25
>> percent in maple-basswood forests heavily invaded by invasive earthworms,"
>> the researchers conclude. "Maple-basswood forests are among the preferred
>> ovenbird habitats in the region, comprise a considerable portion of the
>> region's woodlands.and are experiencing Lumbricus invasions across most of
>> the northern Midwest."
>>
>>
>>
>> Previous studies have demonstrated that invasive earthworms also are
>> harmful
>> to other native North American species, such as salamanders.
>>
>>
>>
>> There is reason for concern that the overall population of ovenbirds could
>> decline, Loss points out. "Ovenbirds migrate to Central America and the
>> Caribbean and back every yea --a trip during which they can fly into
>> buildings and towers or get nabbed by a cat as they rest on the
>> ground--and
>> they also face loss of habitat on their breeding and wintering grounds.
>> Now,
>> here is yet another potential threat to their survival."
>>
>>
>>
>> ###
>>
>>
>>
>> The Smithsonian Migratory Bird Center is dedicated to fostering greater
>> understanding, appreciation, and protection of the grand phenomenon of
>> bird
>> migration. Founded in 1991, it is located at the Smithsonian National
>> Zoological Park in Washington, D.C.
>>
>>
>>
>> "Invasions of non-native earthworms related to population declines of
>> ground-nesting songbirds across a regional extent in northern hardwood
>> forests of North America" is co-authored by Scott R. Loss, Gerald J. Niemi
>> and Robert B. Blair of the University of Minnesota
>>
>>
>>
>>
>>
>>
>>
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>>
>>
>
>
> --
> Jesse Ellis
> Post-doctoral Researcher
> Dept. of Zoology
> University of Wisconsin - Madison
> Madison, Dane Co, WI
>
>
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