Help for Herons at Big Marsh

Over the past several weeks some unusual birds have been stumping Chicago birders at Big Marsh. The conclusion is that they are in the heron family, but compared with the herons typically observed in Chicagoland, something about them is off—they neither look nor act “right.” Are they vagrants? Mutants?

Are they birds at all?

Black-crowned Night-Herons have been a state endangered bird since 1977, but would not be an unusual find at Big Marsh this time of year. They are a colonial wading bird that historically nested throughout the state of Illinois, but their numbers have declined due to breeding habitat degradation and destruction. The largest remaining breeding colony in Illinois nests right in the middle of Chicago, in Lincoln Park Zoo. So, are these mystery Big Marsh herons Black-crowned Night-Herons?

Not exactly.

Conservationists are concerned that such a large proportion of the state population in a single breeding colony at Lincoln Park could predispose the birds to further threats (e.g., an avian influenza outbreak or impacts of a storm event), as well as increase pressures on the nesting habitat (tree health) as the concentration of guano increases. In an effort to minimize these threats and to further bolster this population, a team of researchers from Dr. Michael Ward’s lab at the University of Illinois, Urbana-Champaign has partnered with the Illinois Department of Natural Resources, Lincoln Park Zoo, Bird Conservation Network, and the Chicago Black-crowned Night-Heron Project to identify and develop techniques to encourage some birds to use suitable natural areas that could serve as additional rookery locations.  

Which leads us back to Big Marsh and our mystery herons. The peninsula where these herons have been spotted has been identified by Ward’s team as suitable nesting habitat for Black-crowned Night-Herons and is very near wetland sites where the birds bred up until the early 2000s. That’s when their nesting trees died, and widely fluctuating water levels left nests disposed to predator disturbance and subsequent abandonment of the rookery. Now, researchers hope to encourage some birds to return to this site through a method called “conspecific attraction,” which relies on the tendency of wading birds to spend time near others of their species. This method has been used successfully in other avian conservation programs.  

Last month at Big Marsh, Ward’s team placed 19 Black-crowned Night Heron decoys around the base of the peninsula and in many of the trees, and set up callboxes that play Black-crowned Night-Heron vocalizations at dawn and dusk when the birds are most active and likely to be flying overhead. So, mystery solved—those unusually large, stiff, and still herons are decoys. However, if you see any real Black-crowned Herons or other wading birds interacting with the decoys, researchers would love to hear from you to learn as much as possible about this amazing species.  

Additionally, the team is conducting research on urban Black-crowned Night-Heron foraging behavior and habitat use throughout the Chicagoland area. If you are interested in other potential volunteer opportunities, or if you spot any Black-crowned Night Herons at Big Marsh, please send an email to Sarah Slayton at slayton4@illinois.edu. 

If you spot Black-crowned Night-Herons anywhere in the city, you can also report them using this form to help inform other research efforts this summer: https://arcg.is/0vKHPW0 

To learn more about Big Marsh, read COS’s Calumet Initiative, which includes efforts to restore habitat and conserve birdlife in the Calumet region.