Green Bay Cormorants & Pelicans
Fishing for feathered insights
What fish-eating birds can teach us about the health of Green Bay.
From 2021 to 2023, we teamed up with scientists from the USDA, Wisconsin DNR, U.S. Fish and Wildlife Service and Birds Canada to study the fish-loving birds of lower Green Bay. These piscivorous birds—like cormorants, herons and terns—aren’t just cool to watch; they’re key players in the food web. By tracking where they feed and what they eat, we get a clearer picture of how energy flows through the ecosystem. The better we understand their habits, the better we can protect the waters and wildlife of our region.
Primary Objectives
We tracked the numbers, diets and daily hangouts of fish-eating birds to see how they fit into the local food web—and what that says about the health of our ecosystem.
Evaluate Birds in Lower Green Bay
We focused on the energetics and spatial dynamics of foraging by large, colonial and piscivorous birds in lower Green Bay, particularly Double-crested Cormorants (Nannopterum auritum) and American White Pelicans (Pelecanus erythrorhynchos).
Assess How Birds Influence Fish
Little was known about the impact of large fish-eating birds on lower Green Bay’s fish community, including economically important walleye, yellow perch and other fisheries, as well as populations of undesirable invasive species like round goby. We assessed how birds influence fish populations in Green Bay.
Provide More Ways to Understand Ecosystems
Through the first two objectives, we provided a foundation for lower Green Bay trophic models that include piscivorous birds. Trophic models are essentially the food chain and visualizes the energy flow between living things.
Project Timeline
With funding from Wisconsin Sea Grant, Robert Howe, Amy Wolf and Erin Giese led this project in collaboration with other scientists (Brian Dorr, Brad Smith, Josh Martinez and others). Several graduate and undergraduate students also spearheaded this project through field work. Two master's theses were completed by graduate students Jacob Woulf and Brandon Byrne.
Summer 2021
During the summer of 2021, Cofrin Center faculty, staff, and students and biologists from other organizations captured and attached transmitters to 33 Double-crested Cormorants from the Cat Island Restoration Site. They attached CTT GSM transmitters that use the cellular network and solar power for tracking exact movements of individual birds to 12 Double-crested Cormorants. Of the remaining 21 birds, they outfitted cormorants with CTT Power Tags (TM), which emit signals that are detected when within range of radio towers to infer presence of cormorants.
April-November 2021
Researchers conducted surveys every other week to estimate bird populations of any fish-eating bird species across the lower bay, including the use of drones.
Summer 2022
Students captured foraging behaviors of individual Double-crested Cormorants and American White Pelicans and collected regurgitated pellets, which were dissected in the lab to identify consumed fish of a cormorant or pelican. They also attached transmitters to American White Pelicans to document and better understand their seasonal movements.
Early 2023
The project ended in early 2023 and produced bird population estimates and foraging patterns of piscivorous birds in lower Green Bay, a detailed diet analysis and distributions of fish prey.
Ask an Expert
Meet Erin Giese, Associate Director of the Cofrin Center for Biodiversity. She champions student experience and truly enjoys training the next generation of scientists. If you have questions about this project, Erin can help!