Where people are, wrens aren't

By JACK NISSEN
Capital News Service
LANSING — That short burst of tweets you hear from wrens might be the best way to tell if they’re near, but it isn’t the only way.
A good way to predict the bird populations in the Great Lakes is to listen not for the songs of wrens, but for the roar of car engines. A recent study in the Journal of the Society of Wetland Scientists shows where humans are and where wren populations should be – but aren’t.
One of the broadest research projects on two species of wrens in the Great Lakes region found that urban development has a primary influence on where the birds live.
For the most part, where you find people is where you likely won’t find wrens. And the Department of Environmental Quality identifies human development, like agriculture and industry, as key factors in the loss of wetlands, the primary habitat for these birds.
“Human development of the landscape proved to be the best model for predicting where these species can be found,” said Hannah Panci, a member of the Natural Resources Research Institute at the University of Minnesota Duluth and the study’s lead researcher.  
“Using this information is key to understanding where we can find these species. If we know where these species live, we can better understand how to manage potential human development around the areas.”
Sedge wrens look for shrubs and wet grasses to nest in, while marsh wrens choose cattails and bulrushes.
Sedge and marsh wrens tend to avoid roads and settlements, the study found. The exception is when cropland is near. Marsh wrens in particular liked farmland even when people were nearby.
“Sedimentation and nutrient overload, consequences of agriculture, create a favorable climate for this habitat growth,” Panci said.
Panci notes that the connection between the invasive cattail species Typha angustifolia and agriculture helps explain why cropland attracts marsh wrens.
“Human impact changes the dynamic of wetlands,” said Steven Miller, an assistant professor in the Agricultural, Food and Resource Economics Department at Michigan State University. “Agriculture has a big impact because of the chemical runoff and erosion effects.”
Because chemical runoff and erosion change the dynamic of the wetlands, it’s changing the preferable habitats these birds look for, a status reflected in studies like Panci’s.
Panci’s study was conducted over three years. It used data and maps that quantified vegetation, landscape variables and roads at 840 sites that were analyzed for the presence of the birds.
The loss of wetlands to roads and houses isn’t bad just for birds. Wetlands provide an abundance of benefits to a much broader environment.
“Wetlands provide tons of functions, like way off the charts in their value,” said Patrick Doran, the conservation director at the Nature Conservancy for Michigan. “They provide habitats for birds, they provide spawning areas for fish we like to catch, they filter water, they attenuate storm surge and energy.”
They’re also important for recreation, Doran said. From bird watching to fishing, wetlands have become hotspots for human development. That’s a key component to Panci’s study in understanding the influence humans have on wren populations.
“A natural tension exists between human development and environmental sustainability that creates problems for the ecosystem,” Doran said. “People want to live near wetlands, but by doing this they are offsetting the balance that these environments need.”
Coastal wetlands stretch more than 9,000 miles in the Great Lakes region.
The Environmental Protection Agency’s “State of the Great Lakes” report estimates that 50 percent of Great Lakes wetlands have been converted or lost.
Jack Nissen writes for Great Lakes Echo.
ADDITIONAL RESOURCES FOR CNS EDITORS:
“Influence of Local, Landscape, and Regional Variables on Sedge and Marsh Wren Occurrence in Great Lakes Coastal Wetlands”: https://link.springer.com/article/10.1007/s13157-017-0881-9.