Photo by Joel Pond

It’s been about six weeks since the first black-crowned night herons arrived at Lincoln Park. At first, the herons seemed to hang out primarily on the island in the pond at Nature Boardwalk at Lincoln Park Zoo. Over time their numbers continued to grow, and eventually the population exceeded what the island could possibly support. (We observed this pattern last year as well.)

The herons are currently building or refurbishing nests from last year in two rows of trees just south of Nature Boardwalk. They’re frequently seen in small groups on the island at Nature Boardwalk as well, either resting or gathering twigs and sticks for nests.

As part of a long-term study, biologists at the zoo regularly count the birds and track their behavior throughout the course of the breeding season. To our astonishment, we’ve counted as many as 400 herons in the park!

The population counts haven’t stabilized yet, so it will be exciting to see how many end up actually staying here for the duration of the breeding season. Last year the population peaked at around 250 herons. These high numbers are of particular interest because black-crowned night herons are endangered in Illinois. Stay tuned for more updates about the colony as the season progresses.

Vicky Hunt