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.
Lindsay Renick Mayer | EurekAlert!
Preservation of floodplains is flood protection
27.09.2017 | Technische Universität München
Conservationists are sounding the alarm: parrots much more threatened than assumed
15.09.2017 | Justus-Liebig-Universität Gießen
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
17.10.2017 | Event News
10.10.2017 | Event News
10.10.2017 | Event News
18.10.2017 | Materials Sciences
18.10.2017 | Physics and Astronomy
18.10.2017 | Physics and Astronomy