The little bird with a big history: The story of Wisconsin’s kestrel population

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Photo: Janet Eschenbauch

By: Christa Droste

Frances Hamerstrom, the only female graduate student of Aldo Leopold, is highly regarded for her work to protect the Greater Prairie Chicken (Tympanuchus cupido) from extirpation in Wisconsin. But what you might not know is that Fran was also critical in the recovery of the American Kestrel (Falco sparverius) population.

After moving from Boston to the Buena Vista Grasslands area in Wisconsin Rapids to study under Leopold, Fran indulged in her love for raptors and began working with eagles and harriers.  In 1967, Hamerstrom observed only two breeding pairs of kestrels on the Buena Vista Grasslands, and believed their numbers would improve if additional nesting opportunities were provided.  A year later, she erected 40 newly-built nest boxes, giving birth to the Central Wisconsin Kestrel Research —a long-term monitoring project she led for 30 years until her death in 1998.  Shortly after Fran’s passing, the Wisconsin Department of Natural Resources and the Aldo Leopold Audubon Society breathed new life into the project by installing new nest boxes and continuing to monitor and band the kestrels.  In 2004, Janet Eschenbauch, her daughter-in-law Amber, and three very dedicated volunteers, Maureen Brocken, Sally Ellingboe, and Gerry Janz, proudly took over the project.

The American Kestrel, also known formerly as the sparrow hawk, is a grassland predator critical to maintaining shrew and mouse populations. Kestrels have a large range that extends from southern South America to the boreal forests of Alaska and Canada. However, it is estimated that kestrel numbers have actually declined by as much as 48 percent in most of the eastern United States. “Stable numbers in the central United States are offset by sharp declines in the northeast and west coast,” explained Janet Eschenbauch, director of the program.

Although kestrels require open spaces, they are secondary-cavity nesters that tend to utilize old woodpecker holes, natural tree cavities, and rock crevices. They also nest in small openings found on buildings, making them well-suited to human-dominated environments such as New York City, where you can find a healthy breeding population.  However, a combination of the loss of small farms, urbanization, and reforestation has limited habitat and food that kestrels require to thrive in their range.  Additional anthropogenic-related threats such as communication towers, wind farms, pesticides and rodenticides have also aided in their decline.

On the bright side, kestrels are one species that may benefit from climate change.  As a generalist that preys on rodents, snakes, insects, small lizards, and even small birds, they are likely to fare better than species that specialize on a particular food source. Phenotypic mismatch has also allowed kestrels to begin nesting earlier (21 days earlier than 20 years ago), allowing them to claim territories sooner, giving kestrels an advantage in successfully rearing and fledging chicks.“Fledglings are a bit older, stronger, and wiser when they begin migrating south,” explained Eschenbauch.  However, she added that the changing climate “also brings late winter and early spring storms, which may cause an increased rate of nest failure.”  Furthermore, prey species such as frogs and snakes that depend on snowpack for insulation may be negatively impacted by an annual reduction in winter precipitation.  However, rodents will most likely benefit from warmer weather, providing kestrels with a bountiful food supply.

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American Kestrel. Photo by Flickpicpete via Flickr Creative Commons.

Central Wisconsin Kestrel Research has two primary goals: 1) establish more nesting kestrels on the Buena Vista Grasslands, and 2) collect data on how management practices impact nesting kestrels.  Eschenbauch described the first as an active success, while the second goals has not been addressed yet. Each year, the group bands more than 100 chicks and as many adults as they can get their hands on. Data from banding combined with nest box monitoring reveals information such as clutch size, nest site fidelity, and general population stability and health. The long-term monitoring information on kestrel productivity “may offer insights into the cause of the population decline, revealing important information about what might be influencing downward trends,” Eschenbauch said.  Annual banding data for the Buena Vista Grasslands indicates that the number of fledglings have remained stable, thanks to the group’s efforts. “Field research is a very rewarding experience for all of us – this not a job, but a passion,” Eschenbauch said.

Sharing data, advice, and know-how with other researchers is an important part of the research program’s work.  The program collaborates with the Department of Natural Resources, local landowners, and the Raptor Education Group, Inc., a raptor rehabilitation center based in Antigo, WI, to place young kestrels in age-appropriate nest boxes.  “It gives the orphans a chance to grow and fledge with natural parents,” Eschenbauch explained.  The program’s expertise is also shared with up-and-coming practitioners through a Raptor Field Techniques class taught by Eugene Jacobs in conjunction with the Linwood Springs Research Station.  “Sometimes it is doing things outside the normal realm of field research that brings us the greatest joy,” Eschenbauch said.

So, what can you do to help? The greatest contributions to the program are made through donations of volunteer time and financial support. Through their Adopt a Kestrel Nest Box Program, you can adopt a nest box for $50, which is used to replace worn-out nest boxes, replace equipment, and cover travel monitoring costs. Aside from donations, the program stresses education and involvement in ornithological conservation groups and initiatives across Wisconsin such as the Christmas Bird Count and the Wisconsin Bird Conservation Initiative. Private landowners can also make a huge impact by using alternatives to rodenticides, which poison raptor prey, often harming and killing their natural predators.  The program also urges people to be aware of their local wildlife rehabilitates and know how to contact them regarding injured wildlife.

To find out more and get involved with Central Wisconsin Kestrel Research, please visit the program’s website at: