Black-crowned night herons have returned to Lincoln Park! On Wednesday, March 14, we saw the first three adults resting in some trees on the island in the pond at Nature Boardwalk at Lincoln Park Zoo.
In previous years, adult black-crowned night herons have arrived at Nature Boardwalk around the beginning of April. However, in keeping with our months-long trend of seeing slightly offseason birds—probably due to the extremely mild winter—the herons have arrived considerably earlier this year. (A few juveniles seem to have spent the majority of the winter at the site.)
Scientists at Lincoln Park Zoo’s Urban Wildlife Institute have studied black-crowned night herons near Nature Boardwalk for the last two years. Herons show high nest site fidelity, meaning they tend to return to the same place to breed year after year. Lincoln Park Zoo has records of them breeding in the area since 2007.
Because of the Urban Wildlife Institute's long-term study, we’ll be able to see how this historically mild winter and warm spring influence the timing of certain milestones in the birds’ breeding season, such as evidence of the first hatchlings. We already know they’re getting started earlier than in previous years.
Black-crowned night herons are endangered in Illinois. Lincoln Park Zoo works together with the Chicago Park District and the Illinois Department of Natural Resources to ensure the birds have an opportunity for a successful breeding season in such a highly urban area. Last year there were about 400 adult black-crowned night herons at the population's peak. We’ll have to wait and see what happens this year, but so far we're off to an early start!