LINCOLN PARK — Now that the black-crowned night herons have headed south for the winter, it's once again safe to enter the Children's Zoo at Lincoln Park Zoo.
The endangered birds nest in tight-knit colonies, and they were so thick in the trees above the entrance to the Children's Zoo this summer that the zoo felt compelled to put up "Pardon Our Mess" signs to warn visitors of all the droppings.
Jazmin Rios, of the zoo's Urban Wildlife Institute, said she saw one daycare group of children stop to put hats on before going through.
It's a good problem to have, however, as the population of black-crowned night herons bounced back this summer after a couple of lean years.
The institute counted less than 200 of their nests last winter, down from the mid-200s at the end of 2015 and 2014. Researchers will get a more accurate nest count after the trees lose their leaves, but Rios reported Wednesday that the institute had counted 403 of the birds this year, the same as in spring 2013 when it went on to count more than 600 by the end of the summer.
"The trend is good," Rios said. "They're actually doing much better. The young are surviving here and thriving."
The birds, endangered in Illinois, are "unique to Lincoln Park," Rios said. It's the only known place in the state where they congregate, thanks to the abundant trees and water.
About two feet long, with a black cap and back, gray wings and a white belly, they were first spotted in the area 10 years ago, and have generally been turning up in increasing numbers, especially since the zoo converted the South Pond with its Nature Boardwalk in 2010.
"This is a perfect spot for them," Rios said. "They do come back to the same nesting grounds."
The birds congregated this year above the Children's Zoo entrance near the wolfpack, and also south of the pond in colonies near the Abraham Lincoln statue and behind the Couch family tomb at the southern end of Lincoln Park.
Their nests are a distinctive array of sticks jutting out in all directions. "To me, they're goofy-looking," Rios said. "I think I can make a better nest just throwing 10 sticks together."
But the birds seem to know what they're doing. Rios added that, because of the close-knit colonies, researchers who spot a fledgling on the ground can place it back in any of the nests above and it will be cared for by adults.
More than a dozen nests of black-crowned night herons are in the trees behind the Couch family tomb at the south end of Lincoln Park. (DNAinfo/Ted Cox)
According to Rios, most of the adults have left at this point, heading south to winter in Florida and Mexico. The handful left are younger birds, grayish in color and yet to develop the black crown of their breed, which comes in after two years. They'll no doubt follow along after the Hawk — Chicago's notorious winter chill — starts blowing in off the lake, however, and their migratory instincts finally kick in.
Rios said researchers would someday like to know if Lincoln Park is proving to be a healthy breeding ground because it's drawing birds from both Florida and Mexico, making for genetic intermingling. But they have yet to initiate a program to individually band the birds for a variety of reasons, in part simply to let the flock thrive.
While they congregate on the zoo grounds near Lake Michigan, Rios said they've proved adaptable to the urban environment as well.
One was recently spotted on the Riverwalk, taking a break on a railing while patrolling the river for food.
Rios said she'd also recently heard of a bird feeding on discarded ceviche in an alley. It was almost certainly a black-crowned night heron, she said.
People "were trying to shoo it away and it wouldn't leave," she added. "They are rowdy. You'll hear them scream at you."
Rios said zookeepers sometimes have to shoo them away from trying to steal fish, meat and other food out of exhibit areas, and she's also seen a goldfish inexplicably on the sidewalk — most likely because a black-crowned night heron just happens to have dropped it there.
So beware, owners of Lincoln Park koi ponds. According to Rios, "If they have seen some fish missing, it's probably the herons."