Loss of Whip-poor-wills in Illinois

Photos by Michael Ward.

The eastern whip-poor-will (Antrostomus vociferus), often heard but rarely seen, is an iconic bird of eastern North American forests. Due to their nocturnal habits, whip-poor-wills are well known for their persistent vocalizations of whip-poor-will-whip-poor-will instead of the understated hues of brown, black, gray and white of their plumage. Many have heard this repeating call on warm spring and summer nights in Illinois, although unfortunately, this herald of summer has largely disappeared from many locations throughout the state.

Whip-poor-wills are not monitored as closely as other birds in Illinois due to their nocturnal nature, but the best available data suggest a 70 percent decline over the last 50 years. Researchers at the University of Illinois at Urbana-Champaign began conducting research on whip-poor-wills in 2019 to better understand their ecology and behavior and to ultimately understand why we are losing the species. During our work throughout Illinois, landowners have often commented on the lack of whip-poor-wills, having not heard one in several years, as well as their fond memories of hearing them in the past. The absence of the whip-poor-will’s call represents not just an ecological loss, but a lost connection between the land and Illinois residents.

Our monitoring efforts suggest the species has been extirpated in many locations, but a few strongholds remain. Whip-poor-wills appear to have been extirpated from areas in east-central Illinois (Champaign and Vermilion counties) and much of the northeast (Cook and Lake counties), except for Illinois Beach State Park along Lake Michigan, the only known breeding ground in the area. The largest populations are in Mason County, including in Sand Ridge State Forest, with some whip-poor-wills persisting in many locations in southern and western Illinois, and the species persisting in a few areas in Iroquois County.

With the disappearance of whip-poor-wills comes the question, “why are they declining?” There are many possible causes for the decline of any migratory bird species. In the case of whip-poor-wills we are investigating the potential roles of:

• Habitat degradation and declines in moth food resources,
• Poor reproductive success and
• Poor survival during migration and/or on their wintering grounds.

One of the more interesting results of our research so far is that 80 percent or more of a whip-poor-will’s diet consists of medium-sized moths (families Noctuidae, Geometridae, Erebidae). Whip-poor-wills are aerial foragers, sallying from a perch to capture a moth before returning to their perch. To do this, whip-poor-wills rely upon their large eyes and moonlight to feed on the backlit moths. In his thesis research conducted in 2019 and 2020, Ian Souza-Cole (former MS student at the University of Illinois) found that whip-poor-wills are more easily detected on nights with a full or nearly full moon. Since whip-poor-wills prefer to eat moths, there is a strong association between moth abundance and the presence of whip-poor-wills. As many Illinoisians might remember, a drive through the country at night a couple decades ago would be accompanied by a “bug-splattered” windshield. These days, however, in many areas of Illinois windshields are clean of insects. Therefore, we are conducting research to understand what factors are influencing the distribution, abundance and declines of moths in Illinois (these efforts are being led by Grant Witynski, a PhD student at the University of Illinois).

Many species are thought to be declining due to poor reproductive success (i.e., they do not produce enough young to compensate for natural mortality). Sarah Stewart (former MS student at the University of Illinois) recently completed her thesis investigating the reproductive success of whip-poor-wills breeding at Sand Ridge State Forest and Sand Prairie Scrub Oak Nature Preserve in Mason County. Whip-poor-wills are interesting birds as they only lay two eggs and do not make a nest, but rather simply lay their eggs on the forest floor, often on top of oak leaves. The eggs are incubated for 20 days before they hatch. After hatching, whip-poor-wills are semi-precocial, meaning they can move from the nest but still need care from their parents. The parents provide care to the young for 15 days until they become able to fly. Even after the young are able to fly, the parents continue to provide care for another 30 days. While the results of this study are still being analyzed, it appears that the reproductive success of whip-poor-wills at these two sites, which still retain robust whip-poor-will populations, is relatively good in some years, but not in others. More research is needed to understand the drivers of year-to-year variation in reproductive success of whip-poor-wills as well as the productivity of the species at other locations throughout Illinois.

As with many of our birds in Illinois, we share these birds with other regions. The decline of whip-poor-wills has not only been noticed in Illinois but has attracted the attention of researchers across North and Central America. In collaboration with researchers at the Ohio State University, the U.S. Forest Service, and others, we attached GPS trackers to whip-poor-wills in Illinois and other Midwestern states to determine where the species spends its winters. We found that the whip-poor-wills in the Midwest winter in southern Mexico and northern Central America. We also learned that they leave Illinois in late September and early October and do not cross the Gulf of Mexico but rather migrate along the coastal areas of Texas and northern Mexico. We are currently working in southern Mexico to determine whether declines of whip-poor-wills in Illinois could be related to issues impacting survival of whip-poor-wills in southern Mexico. As in other regions, loss of forest to agricultural expansion and the use of insecticides may be impacting whip-poor-wills during winter. We have conducted two trips to the region to collect preliminary data and plan to conduct more extensive work in the winter of 2023-24.

While there is much more research needed to determine the specific factors that are impacting whip-poor-wills, actions to help maintain current populations (or potentially lead to the return of whip-poor-wills) likely include an increased emphasis on forest management. Over the last several years we have noticed more whip-poor-wills in forests that have been managed via prescribed burns, invasive species removal, and selective tree removal. In contrast, forests that have become dense due to invasive species appear to have few or no whip-poor-wills. Currently, Holly Coates (MS student at the University of Illinois) is conducting research on the question of how forest management affects whip-poor-wills and the reasons why whip-poor-wills seem to prefer open woodlands. The results of this research may lead to more specific recommendations for improving whip-poor-will habitats.

In summary, whip-poor-wills are experiencing widespread and dramatic declines in Illinois and many other regions. It is likely that multiple factors are contributing to the loss of this species. As research continues, we hope to inform the public about specific actions that can be taken to help this species. Preliminary research suggests that to help whip-poor-wills we need to help moths. Actions such as planting native plants, maintaining unmanicured areas for moth populations to overwinter, and reducing the use of pesticides may benefit both moths and whip-poor-wills. Moreover, an increased emphasis on forest management may help both moths and whip-poor-wills as well as many other declining birds that are dependent on open woodlands.

Dr. Michael Ward is a professor with the University of Illinois and senior ornithologist with the Illinois Natural History Survey. Dr. Ward is involved with a large number of collaborative research projects with foci on avian ecology and behavior.

Ian Souza-Cole received his M.S. from the University of Illinois in 2021 studying the ecology and behavior of eastern whip-poor-wills. He is currently a Senior Coordinator for Audubon in Sacramento, CA.

Sarah Stewart received her M.S. from the University of Illinois in 2023 studying the ecology and reproductive success of eastern whip-poor-wills. She is currently an avian biologist for the South Carolina Department of Natural Resources.

Grant Witynski is a PhD student co-advised by Dr. Ward and Dr. T.J. Benson. He earned his B.S. in Conservation Biology from the University of Wisconsin–Madison. He is broadly interested in avian biology and entomology, with an emphasis on the ecology of declining species. 

Holly Coates is an M.S. student at the University of Illinois Urbana-Champaign, studying the effects of forest management on eastern whip-poor-wills and Chuck-will’s-widows. She completed her B.S. degree at the University of California Davis and aspires to work in applied avian ecology.

Dave Edlund received his B.S. in Natural Resources and Environmental Sciences at UIUC in 2022. He has since been coordinating the Midwest Eastern Whip-poor-will Project in the Ward Lab of Ornithology to determine possible factors contributing to the declines of whip-poor-wills in Illinois, Missouri, Michigan, Wisconsin and Ohio. In the spring of 2024, Edlund will continue whip-poor-will research as a master’s student for Dr. Ward.

Thomas J. Benson is a Senior Wildlife Ecologist at the Illinois Natural History Survey and Research Associate Professor with the Department of Natural Resources and Environmental Sciences at the University of Illinois at Urbana-Champaign.