The red-shouldered hawk is a state-threatened, medium-sized, forest-dwelling raptor that tends to be secretive in nature.

Very little is known about these “phantoms of the forest,” and there is a need by foresters, ecologists, biologist, land managers and other professionals to understand what specific habitats these elusive birds are using for their summer home range, migration routes, and winter habitat.

In 2018, the Foundation provided support for the Northeastern Wisconsin Audubon Society to fill that gap by funding the first attempt to monitor Wisconsin’s red-shouldered hawk with more advanced telemetry technology, or monitoring via radio transmitters. 

An adult red-shouldered hawk wintering in WI. Photo by Gene Jacobs.

How it all works

Adult red-shouldered hawks are safely captured at their nest site during the breeding season (March-August), attached with a solar-powered GPS logger transmitter and released.

These loggers track the hawks’ movements, which helps determine their breeding range, nesting and breeding habitat use, migration patterns, as well as wintering areas and winter habitat use. 

A red-shouldered hawk is equipped with a solar-powered logger and ready to provide the team with valuable data. Photo by Carter Freymiller.

Above you can see a red-shouldered hawk with a solar-powered logger. It may look large or even cumbersome, but not to worry – the loggers do not harm the birds!

These devices weigh less than 3.0% of the bird’s weight and have undergone years of tests by the United States Geological Survey Bird Banding Lab (BBL) to ensure they do not restrict the bird’s flight. The BBL also controls the deployment of these transmitters to only highly trained individuals to ensure the transmitters are attached properly.

Spring migration surprises

Earlier this year the red-shouldered hawks being monitored made their northward spring migration back to their breeding territories. The Audubon team, Matthew Hanneman, Gene Jacobs and John Jacobs, was fortunate enough to receive complete migration data from two hawks (one male and one female) equipped with loggers.

Above is an example of the data they received for one of the female hawks. They were surprised to see that not only did she remain in Wisconsin for the winter, but she remained in the Nicolet National Forest near her breeding territory. This was only the second time in the study that the team observed a female red-shouldered hawk equipped with a logger remaining in Wisconsin for the winter.

(Left) Gene Jacobs counts nestling red-shouldered hawks at a nest in central WI.
Photo by Matthew Hanneman 
(Right) An adult red-shouldered hawk delivers food to three hungry chicks in northeast WI. Photo by John Jacobs

Come rain, or shine, humidity or mosquitoes . . .

The teams’ 2020 field season wrapped up earlier this summer, and was not without a few challenges.

From early April through late June they endured cold and snow then heat, humidity, ticks, and mosquitoes as they visited nests within their central Wisconsin and northeastern Wisconsin study sites. Even with the COVID-19 pandemic spreading across the country they managed to stay socially isolated and complete their field work.

In the end, their hard work paid off. In central and northeastern Wisconsin, the team found a total of 47 active nests (of which only 26 were able to successfully produce nestlings). Together the team banded 46 nestlings and 10 adults, as well as equipped loggers to 4 of the adult hawks.

Matthew Hanneman with an adult remale red-shouldered hawk banded and equipped with a logger in central Wisconsin. Photo by Carter Freymiller. 

Monitoring Mercury Contamination

In addition to the telemetry research, their UW-Stevens Point graduate student Matthew is also investigating mercury contamination in red-shouldered hawks at the study sites.

We often associate mercury contamination with aquatic ecosystems and are sometimes advised not to eat fish from certain water bodies. Typically, birds like bald eagles, osprey, and loons have elevated mercury levels since their diets consist primarily of fish.

While red-shouldered hawks do not typically eat many fish, they do eat many small amphibians and reptiles and they nest close to water sources. This summer Matthew collected blood and feather samples from nestling and adult red-shouldered hawks which will be analyzed later this fall for mercury content. 

(Left to right, top to bottom) Black bear, scarlet tanager, red-backed vole, star-nosed mole, wood turtle, wood frog. Photos via Canva.

Preserving red-shouldered hawk habitat

The telemetry study will continue on into 2022, and the information gathered will allow foresters and wildlife managers to make more informed decisions about the protection and preservation of this state-threatened species and its habitat.

The data collected through this study will also likely benefit many other species that utilize the same habitat as the red-shouldered hawk, such as red-backed voles and star-nosed moles, scarlet tanagers, broad-winged hawks, and cerulean warblers, salamanders and wood frogs, wood turtles and even bears.

Thank you for your membership and support of the Foundation and for making this important work possible!

Northeastern Wisconsin Audubon Society is a local, volunteer-based Chapter that shares the National Audubon’s vision to protect birds and the places they need, today and tomorrow, throughout the Americas using science, advocacy, education, and on-the-ground conservation.  They focus this vision on the birds and habitats of northeastern.