LINCOLN PARK — More than 50 mature trees in Lincoln Park that frequently serve as nesting sites for an endangered species of birds are set to be cut down over the next two years.
The trees, a mix of ash and Linden oaks, have become a nesting site for black-crowned night herons over the past six years as the birds repopulated the area.
The revitalization of the heron population in the park has been called "a great success story" by experts at the Lincoln Park Zoo, but many of the trees where the birds nest year after year are damaged and diseased.
The ash trees have been struck by the Emerald Ash Borer, which has plagued much of the country, and the Lindens have been structurally compromised, according to Jason Steger, natural areas manager for the Chicago Park District.
"From our standpoint, we know these trees have to come down," he said.
The herons, which are stocky, yellow and black and about the size of a football, made their comeback into the Lincoln Park area in 2007, starting on the island surrounded by the zoo's south pond, according to Mason Fidino, the zoo's coordinator of wildlife management.
As their numbers increased, some of the herons made their way to the row of trees near the Benjamin Franklin monument at the south end of Lincoln Park.
There were about 20 nesting pairs of the birds in 2008, but that number grew to 250 nesting pairs this past summer, or a total of about 500 birds, Fidino said.
It is likely the largest nesting colony in the state, Fidino told DNAinfo Chicago in a 2013 interview.
The black-crowned night-heron was placed on the Illinois endangered species list in 1977, and there are only four sizeable colonies remaining in the state, according to Illinois Natural History Survey.
The 57 trees that are set to come down in two waves, the first will likely be in March and the second will be next year, according to Steger.
The Chicago Park District has been working with its partners at the Illinois Department of Natural Resources, the U.S. Fish and Wildlife Service and the Lincoln Park Zoo for five years to determine how to solve the problem, Steger said.
The park district hasn't settled on a species list for the trees that will replace those that are uprooted, but it is working with a Lincoln Park historian.
"We understand they were planted with elms so we are trying to stick to that historical landscape element as well," Steger said.
There are currently four colonies of the herons that migrate to Lincoln Park around April 1 each year and the area that is going to be cut down is home to one of the larger colonies.
The nesting area that will be lost comprises around 40 percent of the total, Fidino said.
Hatchlings typically emerge in the middle of May before the birds fly south around September.
Fidino said the birds that typically nest in the area that will be lost will either join one of the other three colonies or try to start a new colony, which is the riskier choice.
"It's a big success story and I hope the birds will be able to adapt to this next problem," Fidino said.
When the birds come back in April Fidino will be out there doing his daily counts, as he has been since 2007.
Fidino is hopeful that the reintegration will be seamless.
"I'll be seeing them when they show up, so I'm ready for them," he said.