Tracking the Endangered Black-crowned Night-heron

Photos courtesy of the authors.

When thinking about endangered wildlife, we often think of small populations persisting in remote, pristine habitats with few humans on the landscape. And yet the urban landscape of Chicago, with dense skyscrapers and millions of human residents, is home to an often overlooked, state-endangered wetland bird—the black-crowned night-heron (Nycticorax nycticorax).

Black-crowned night-herons (BCNH) are colonial waterbirds that typically nest in large rookeries year after year, finding safety in numbers from predators that prey on their eggs and chicks. While these birds were once abundant throughout Illinois, breeding in wetlands across the state, years of anthropogenic habitat degradation and destruction have led to night-heron population declines and the eventual inclusion of this species on the Illinois Endangered and Threatened Species List in 1977. At that time there remained two historic population strongholds, one in the Lake Calumet region near Chicago and another in the Metroeast area of East St. Louis.

Large night-heron rookeries in the Calumet region remained until 2010. At that time, the last breeding herons abandoned their historic colonies, dispersing to other habitats in Chicago’s Lincoln Park and on private land in Indiana. The last known colony in the Metroeast area persisted until 2007 when the final 150 pairs deserted their breeding grounds in Alorton (St. Clair County) and dispersed across the Mississippi River to colonies in north St. Louis. Since then, the only significant BCNH breeding colony left in Illinois has been in Lincoln Park, Chicago, where a small population settled in 2007. Since then, the population has grown and moved between several locations within Lincoln Park, including the Pritzker Family Children’s Zoo at Lincoln Park Zoo, where the birds have been nesting since 2012.

Now, the rookery at Lincoln Park Zoo appears to be flourishing. The past two years have been the most prolific years for the colony since 2010, with 751 and 686 adult herons detected in 2022 and 2023, respectively. Indeed, 2023 was the most productive breeding season for the colony on record, producing 486 young.

Despite this local population level success, there remain conservation concerns for these birds across Illinois and the central United States. With herons densely concentrated in a single location, there is a greater risk of a catastrophic, random event, such as severe weather or disease outbreak (e.g., avian influenza), leading to destruction of the colony.

Additionally, life in a highly urbanized environment can involve additional environmental pressures such as limited breeding habitat, urban pollutants and harmful interactions with people. However, it is well documented that urban living can provide easier access to food resources for wading birds, potentially offsetting the disturbances associated with residing in an urban environment. Understanding how all these factors impact the ecology of these birds is key to furthering their conservation in Illinois. To address these conservation concerns, researchers at the University of Illinois, Illinois Department of Natural Resources and Lincoln Park Zoo Urban Wildlife Institute are studying BCNH movement, behavior, and health to better understand their urban habitat use and identify additional potential rookery sites in a preemptive effort to support the continued existence of this species in Illinois.

The goals of this research are three-fold: 1) study heron movement and habitat use in Chicago to identify critical foraging grounds and potential new rookery locations, 2) collect biological samples to assess population health, with specific interests in heavy metal pollution and various pathogens, and 3) establish new rookeries by attracting birds to suitable locations using conspecific cues.

During the spring and summer of 2023, scientists successfully banded 16 BCNH and equipped 7 birds with satellite transmitter “backpacks” that collect GPS locations at regular intervals. This data will provide information about the birds’ daily movements across the Chicagoland area and track birds on their migration to their wintering grounds. Scientists also collected feather samples to measure birds’ heavy metal exposure, which will provide key information about the population’s health and quality of their forage base. Additionally, researchers employed the concept of “conspecific attraction” at Big Marsh in Calumet and four locations near St. Louis Metroeast to attract birds in search of new breeding grounds. For that aspect of the project, BCNH “decoys” were deployed to suitable nesting trees and BCNH and other heron vocalizations were broadcast throughout the breeding season during the hours the birds are most active with the hopes that the “presence” of other BCNH would encourage some birds to establish new rookeries in these protected, natural areas. Although we found no evidence of birds nesting in these locations this season, there were sightings of BCNH roosting in the trees near the Big Marsh site and other heron species occupying some Metroeast sites. By pursuing multiple approaches, the research team hopes to promote the persistence of BCNH in Illinois as well as pioneer new conservation tactics that may be applicable to other threatened wading bird species.

Additionally, the nature of this research taking place in a large metropolitan area has facilitated close partnerships between researchers and local organizations and agencies. Groups such as the Chicago Black-crowned Night-heron Project, Bird Conservation Network, and the Chicago Park District were critical in helping get this project off the ground and providing financial, volunteer and logistical support throughout the first field season. This collaboration has helped address some of the unique challenges of trying to protect an endangered species in a big city and could serve as a model for conservation throughout the country.

Looking to the future, members of the research team are working with these community partners to prepare for next year’s breeding season. Scientists hope to triple the number of tagged BCNH from the Zoo colony, collect more samples to explore various aspects of heron health and diet, and use movement data from the first round of tagged birds to identify at least one more potential rookery location in the Chicagoland area. Visit the Ward Lab website to learn more about this project.

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Sarah Slayton is an M.S. student in Dr. Michael Ward’s lab at the University of Illinois at Urbana-Champaign. She is broadly interested in applied conservation research with specific interests in urban ecology and conservation, habitat choice and use, and wildlife management planning. Currently, she is studying the movement ecology and conservation of black-crowned night-herons in the Chicago area and manages much of the day-to-day fieldwork for this project.

Michael Avara is the avian lab manager and field coordinator at the University of Illinois at Urbana-Champaign. He supports lab data collection and analysis on the many diverse research projects in the Ward Lab. This includes managing the Illinois Motus Network of 17 telemetry towers across the state, working with organizations in the St. Louis Metro East to restore endangered waterbird colonies, conducting field surveys to quantify bird populations, and analyzing acoustic data to help refine understanding of Illinois chorus frog behavior and distribution.

Dr. Michael Ward is a professor at the University of Illinois at Urbana-Champaign and an Ornithologist with the Illinois Natural History Survey. His research focuses on avian ecology, behavior and conservation, with specific interests in migratory and special-status species. He has worked on dozens of research projects related to avian movement and habitat selection and has developed novel approaches to species conservation.

Henry Adams is the Lincoln Park Zoo’s Urban Wildlife Institute Wildlife Management Coordinator. They have 10 years of experience researching the health of wading birds and other taxa in urban and exurban environments. They coordinate and execute research efforts, assist in graduate student supervision, establish community partnerships, and assist in sample and data analysis while driving the dissemination of this work’s findings to various audiences and stakeholders.

Brad Semel is the Endangered Species Recovery Specialist for the Illinois Department of Natural Resources, leading statewide conservation efforts for state and federally listed species. He is responsible for coordinating academics and professionals within state and federal agencies to develop adaptive resource management guidelines and novel approaches and techniques for the conservation of rare species and provide oversight and training to professionals in specialized areas of statewide recovery efforts.