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.”
Some 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
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