Double-crested cormorants make their nest in the trees at Lake St. Clair Metropark.
Photo by Patricia O¨Blenes
HARRISON TOWNSHIP ！ Even in broad daylight, it looks like a scene from a scary movie. Large, black birds line the branches of trees with no leaves ！ dead and dying trees whose dry branches stand in stark contrast to lush green grasses and foliage.
But what has caused the demise of some trees on an island across from the marinas at Lake St. Clair Metropark? The answer is not as clear as it may seem.
The large black birds are double-crested cormorants, a native species of water bird in Michigan, according to Holly Vaughn, public outreach and engagement unit manager for the Michigan Department of Natural Resources.
Vaughn said the birds are not an invasive species; they have called Michigan their home for more than 100 years, but their numbers seem to be increasing in recent years.
＾The birds have always, in migration, roosted in the fall,￣ said Julie Champion, East District Interpretive Supervisor for Huron-Clinton Metroparks. ＾They¨ve never nested in those trees until about two years ago. I¨ve been here since 1990. They weren¨t nesting here.￣
Vaughn explained that it is not uncommon, when groups of water birds, such as double-crested cormorants, herons or egrets, nest and roost together for their guano to kill the vegetation surrounding the nesting area.
＾I know, at Lake St. Clair, there are larger numbers of cormorants that gather. They gather in those trees every night, leave the trees in the morning to go eat, and return. That behavior, just their excrement, is killing the trees. They just have very acidic guano.￣
Champion, who oversees the Lake St. Clair Metropark and Stony Creek Metropark nature centers, said perhaps the largest number of double-crested cormorants she¨s ever seen began nesting in the trees on the island off the coast of the marinas at Lake St. Clair Metropark in 2020. But she doesn¨t think the birds alone have led to the premature death of the trees.
＾What else was happening with that island (is), we went over there in kayaks, and there was no island. It was totally underwater,￣ Champion said.
The Great Lakes basin, which includes Lake St. Clair, saw record high water levels in 2019 and 2020. Prior to that, on the island where the trees grow, swans would lay their nests and deer would give birth to their fawns.
＾It was too quick. Those trees died off in two years,￣ Champion said. ＾I think it¨s the flooding because we¨ve lost a number of trees right out behind the Nature Center. A number of them were fine and healthy two years ago.￣
Cottonwood trees are tolerant to very wet soil, Champion said, but they can¨t survive being submerged for two years.
＾Eventually, cormorants do kill off a tree because of the acidity of their droppings, but it would take a longer period of time, and I think it was the flooding,￣ Champion said.
Beavers may have played a part, as well, she said, weakening the trees with their chewing before the island flooded.
＾All of those things kind of happened together,￣ she said.
If the trees eventually fall, Champion said the birds may have to move on to different nesting grounds. She surmised that may have happened elsewhere in the Great Lakes, which is why they have come in droves to Lake St. Clair Metropark.
＾What will be kind of interesting is to see, when water levels move back down, where the birds move to,￣ she said.
There were fewer cormorants in the 1940s and 1950s, Champion said. In speaking with a researcher studying the birds in the upper Great Lakes, she said she learned there were increased instances of deformities in the birds noted during those times. According to the National Audubon Society, after the population of the birds increased from the 1920s to about the 1950s, the numbers of double-crested cormorants dropped again through the 1960s, potentially due to the effects of pesticides. Populations began increasing again after DDT was banned in 1972. Their populations have continued to increase, and their range expanded since then.
The double-crested cormorants aren¨t the first birds to make the island their home. Champion said black crowned night herons, a species whose population is decreasing, nested in the trees before the cormorants.
＾What may happen is, as it dries out again, those trees may stand dry for a while. If they fall down, if the water goes down, then just new cottonwoods would grow, but it will take a long time,￣ she explained.
Cottonwood trees are a species that grows quickly, however.
＾I have old photos from when the park opened in the ¨50s. There weren¨t (many) trees on that island, so (they are) 50 years old, give or take. They¨re fast growing,￣ she said.
Champion said she finds cormorants to be very interesting. For a water bird, she said they don¨t have as much waterproofing, which allows them to dive deeper into the water for the little fish they feed on. When they arise, however, they go high up into the trees and spread their wings to help them dry.