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University of Windsor
Kentucky coffeetrees used to measure cormorant damage
When Parks Canada held a cull this spring to reduce the population of cormorants nesting on Middle Island in Lake Erie, it argued that the birds’ guano and nesting habits were ruining the ecosystem for other at-risk species on Canada’s southernmost landmass.~
Now a scientist in the university’s Great Lakes Institute for Environmental Research is studying the effects of their droppings on local vegetation to quantify the extent of the birds’ harm to the island’s natural inhabitants.
Scott Rush, a postdoctoral fellow working for GLIER associate professor Aaron Fisk, is growing 40 Kentucky coffeetrees in the Sandwich Street institute’s open centre courtyard. Twice a day, students pour into the tree pots water that’s been laced with cormorant droppings collected from Middle Island.
“It’s a little gross,” admitted Dr. Rush, a native of Connecticut who completed his PhD at the University of Georgia.
Besides measuring the physical growth of the trees, leaves are collected, freeze-dried, ground up and then vapourized for analysis in a mass spectrometer, which relies on a high-tech laser to determine their levels of contaminants such as ammonium, phosphorous and nitrates. The process is repeated throughout the trees’ growth to measure whether the concentrations of those contaminants increase as the plant develops.
Rush said he’s not certain if bird waste in the soil inhibits the trees’ growth because they can regulate how much nitrogen and carbon they absorb, but he suspects it may promote the growth of other plants that wouldn’t normally thrive there, and ultimately alter the functioning of the island’s ecosystem.
“It can really affect the dynamics of the entire system,” he said.
The cull, held in April and May, was not without controversy. Many local scientists, hoping to restore the island’s biodiversity, supported reducing the cormorant population while some animal rights activists called it inhumane.
Kentucky coffeetrees were selected for the research because they’re fairly common in this region and a good representation of the types of vegetation growing on Middle Island. Rush hopes to publish the results of the study when it’s finished and figures he’ll probably give the trees away then.
— Stephen Fields
Scott Rush watches as research assistant Jacqueline Isaac pours cormorant-dropping-laced water into the pot of a Kentucky coffeetree.