UD doctoral candidate conducts wood thrush studies around Newark

May 8, 2013 under CANR News

The University of Delaware’s Zach Ladin has been studying the wood thrush for the past three years — continuing research started by Roland Roth 37 years ago and continued by Greg Shriver, associate professor in the Department of Entomology and Wildlife Ecology, in his Forest Fragments in Managed Ecosystems (FRAME) program – and is looking at how breeding birds can provide clues to the relative health of the environment.

“We use birds as environmental indicators,” said Ladin, a doctoral candidate in the College of Agriculture and Natural Resources. “When you go to the doctor, they take different measurements, like blood pressure. By itself, your blood pressure may not mean anything but it gives the doctor insight into whether you’re going to have a heart attack soon or whether you’re suffering from some sort of heart disease, or any number of diseases that might be associated with that. So we’re using birds as a window into the health of the forest.”

To do that, Ladin has expanded the territory of the study originated by Roth.

While Roth’s initial study focused solely on the ecology woods located east of Delaware Stadium, Ladin’s study has spread out all over the city of Newark. Using 21 sites around Newark, Ladin looks at how the birds respond to human impacts in an urban landscape, using areas like Iron Hill, the Newark reservoir and White Clay Creek, among others.

Ladin said that Newark is the “ideal place to study urbanization since we’re right in this Mid-Atlantic region. We’re interested in how these birds are responding to an urban landscape.”

Zach Ladin studies wood thrush in UD's ecology woodsSome sites, like Iron Hill, are doing very well when it comes to having large populations of wood thrush, while other sites, such as the small patch of woods across from the hotel at the intersection of Routes 4 and 896, are completely devoid of wood thrush.

Just because a site has a large number of the birds does not necessarily mean that it is a healthy habitat, however. It could simply mean that the wood thrush are “getting pushed out of all the very high quality spots,” said Ladin. “Maybe they were pushed out of White Clay Creek or Iron Hill and this is a last resort for them, so you end up seeing the refugees getting shoved into a very small and isolated spot. It could be a bad sign.”

Ladin explained he trains crews of students that try to locate wood thrush nests, doing so by listening for audible cues, such as when the birds make an alarm call when the researchers get too close to their nests. Once they find the nests, they input the GPS coordinates and monitor the nest every three or four days.

“We keep close track of the eggs,” said Ladin, explaining that sometimes crew members will find eggs from a different species in the wood thrush’s nest. “There’s actually another type of bird called the brown-headed cowbird that will lay its eggs in other species’ nests. It’s called brood parasitism where they’ve evolved a really clever technique. They don’t raise their own chicks, they just go around and lay eggs in other birds’ nests and let those birds raise their chicks.”

Ladin said that while some species can recognize cowbird eggs and remove them from their nests, the wood thrush do not. “There’s an evolutionary arms race going on and the wood thrush have not figured that out quite yet.”

As far as the number of wood thrush breeding in UD’s ecology woods, Ladin said that there are currently around 20 birds per year, which is down considerably from the peak numbers of 70-80 during the 1990s.

Ladin’s research is trying to determine why the numbers are decreasing not just in the sites around Newark but across the eastern United States.

“One of the things we’re looking at is if the soil calcium is a limiting factor for birds, since they need it for their eggshells and the nestlings need it to grow their bones, and this is one of the highest concentrated areas of acid rain in the country,” said Ladin.

Ladin also wants his research to highlight the fact that on the East Coast, especially around the I-95 corridor, there may not be big patches of forests but there are lots of little patches that play an integral role in improving the environment.

“If you add up all these tiny patches of forests that have been subdivided, it’s actually over 1.2 million acres of forest,” said Ladin. “My motivation is to show people that this is highly critical habitat and that you can’t just discount a small patch of forest because its only three or four acres. Those patches provide really important services for us — like helping clean the water, and helping sequester carbon, reducing CO2 from the atmosphere — so we have to make sure we’re out to conserve their proper functioning. Studying the bird response in those patches is one of the best and most cost-effective ways to do that.”

Article by Adam Thomas

Photos by Danielle Quigley

This article can also be viewed on UDaily.

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Center for Managed Ecosystems puts past urban forest research into new FRAME

June 8, 2010 under CANR News

Greg Shriver, assistant professor of wildlife ecology in the Department of Entomology and Wildlife Ecology and research scientist with the Center for Managed Ecosystems at the University of Delaware, is collaborating with the U.S. Forest Service to continue work on a project that focuses on assessing the conditions of urban forests and explores ways in which to improve those conditions.

The project is known as Forest Fragments in Managed Ecosystems, or FRAME, and it has its origins in a study titled “Wildlife Ecology and Urban Impact” conducted 45 years ago at UD by scientists in the Department of Entomology and Wildlife Ecology and the Forest Service.

The 1965 study was continued by Roland Roth, UD professor emeritus of wildlife ecology, beginning in 1972. Although Roth could not have known at the time, Shriver said that his work — conducted on the UD Farm — became the longest running study on the demographics of the wood thrush, a neotropical migratory bird.

Shriver, who subsequently picked up the mantle, called the wood thrush the “hallmark species” for this research and said FRAME builds on Roth’s earlier studies. The FRAME project was initiated as a collaborative effort between Shriver; Vincent D’Amico, a Forest Service scientist stationed at UD; Jake Bowman, associate professor of entomology and wildlife ecology; and Jeff Buler, assistant professor of entomology and wildlife ecology.

Shriver said FRAME is “a fairly large-scale forest fragmentation study aimed at assessing the condition of urban forest fragments to see if we can increase their quality.”

These forest patches dotting the developed landscape “are providing the some of the only remaining habitat for neotropical migratory birds, small mammals, and insects,” he said.

The group is currently establishing long-term plots and surveying the condition of Mid-Atlantic forest fragments.

After assessing the overall health of the forest fragments, Shriver said he and his colleagues will research ways to improve them. “The big picture is that these fragments are providing important ecosystem services — air, water, things required to make the area livable,” he said. “The goal of the FRAME project is to better understand the interactions between soil, water, plants and the animals dependent on them within urban and suburban environments.”

Shriver, who will be aided by graduate students, said the study will be multifaceted, with the first part focusing on multitrophic effects of soil acidification and biodiversity.

“There has been some concern that acidification in soils, especially here in the Northeast, could be limiting the availability of calcium-rich prey — such as snails and isopods — that birds need during the breeding season to make eggshells and feed their nestlings, because the nestlings’ growth rate is so fast and they need so much calcium,” Shriver said. “Studies have shown that if you have limited calcium availability, you have limited calcium-rich prey, which then limits the breeding density and reproductive success of some bird species.”

The FRAME study has broken the Newark area’s urban forest fragments into grids using GPS systems, starting with the original study patch from the Roth study and adding 19 other woodlots.

In each of the fragments, Shriver said he and his students plan to “estimate breeding bird territory density, nest survival, a measure of reproductive success, and species diversity. We’re also taking soil samples and then litter samples to see if we can link the soil pH to calcium-rich prey.”

Shriver explained that a low pH means that the soil has a high amount of acidification, and that “the acidification comes mostly from acid rain, which has been greatly reduced since the height of the Industrial Revolution, but the soils have likely not recovered. Once you push a soil into an acidic state, unless it has some buffering capacity, it is very hard to get it back.”

What happens with soil that has been pushed to an acidic state, he said, is a reduction in calcium-rich prey, which in turn limits food for breeding birds. The birds either have lowered reproductive success or leave that forest fragment.

The first two years of the FRAME study are dedicated to gathering the pre-data, showing the present condition of the soil. Shriver said the research team then plans to “lime the forest patches to see if we can increase their quality, which will raise the pH and release the calcium,” thereby improving biodiversity.

They plan to treat 10 sites with lime and leave another 10 sites untreated in order to compare differences in soil quality. He said he is confident that “changing the pH is going to change a lot to these forest fragments.”

The research team is partnering with the Newark Department of Parks and Recreation, New Castle County Parks, and Delaware State Parks. Shriver said that “without the cooperation and enthusiasm we’ve received from all the partners, this project would not be possible.”

Shriver received a bachelor of science degree in wildlife management from the University of Maine, a master’s degree in wildlife conservation from the University of Massachusetts and a doctorate in environmental forest biology from the State University of New York (SUNY). He joined the UD faculty in 2005.

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