LINCOLN PARK — An endangered bird continues to thrive in the area in and around Lincoln Park Zoo, even though zoo officials noticed a considerable drop in the number of their nests last year.
The black-crowned night heron is considered endangered in Illinois, but it has thrived in Lincoln Park, especially in and around the zoo.
"Birders are concerned," said Carolyn Marsh, a Northwest Indiana bird watcher who reported the drop on the Illinois Birders Exchanging Thoughts website.
Even so, researchers with the zoo's Urban Wildlife Institute counted just 191 of the herons' nests last year, down from 271 in 2015, 263 the year before and even 211 in 2011.
Nonetheless, the zoo reported that "although we had less adults than last year, we still had about the same amount of young as last year. The adults were highly successful breeders this year and the weather cooperated so that we had less deceased young compared to previous years."
"It’s natural for populations to fluctuate from year to year," institute ecologist Mason Fidino said Tuesday. "This year’s count of black-crowned night heron adults is slightly lower than the previous year but is not cause for concern — even stable populations fluctuate around the population level that the environment is able to sustain."
Fidino speculated that shifts in resources such as potential nesting sites and food availability, which vary from year to year, "could be a factor, and given that these birds are migratory, could be the result of events far beyond Lincoln Park."
Fidino said the institute would continue to study the nest count and population for any prevailing trends.
Unlike the larger and more familiar great blue heron, the black-crowned night herons are about 2 feet in length and typically weigh under two pounds. They're formidable predators, however, and according to Fidino they eat fish, lizards, mice and even turtles — "anything they can get their beaks on."
Although rare in Illinois, they formed an initial colony on an island in the zoo's South Pond, and have especially thrived since the adoption of the Nature Boardwalk designed by Studio Gang Architects in 2010.
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