Study system
Research was conducted at Sandhill State Wildlife Area (44.31°N, -90.13°W; hereafter, Sandhill), a 36 km2 wildlife area located within the biological tension zone of central Wisconsin in the midwestern region of the United States (Fig. 2). Sandhill is enclosed by a 2.75 m-tall fence and managed by the Wisconsin Department of Natural Resources to maintain habitat for several species, including ruffed grouse. Sandhill is a complex mosaic of forest types and age classes separated by a network of managed flowages and marshes; the dominant forest types are aspen Populus tremuloides and P. grandidentata and oak and scrub oak Quercus sp. forests (Shipley et al. 2019). Public vehicle access to Sandhill is restricted throughout winter, but there is a limited fall hunting season for ruffed grouse in the southern half of Sandhill.
Grouse are subject to predation from a diverse suite of predators across their range, many of which are found at Sandhill including great horned owl Bubo virginianus , barred owl Strix varia , sharp-shinned hawk Accipitier striatus , Cooper’s hawkAccipiter cooperii , northern harrier Circus hudsonius , bobcat Lynx rufus , and coyote Canis latrans (Rusch et al. 2020). Grouse populations in the midwestern United States are most vulnerable to predation by hawk and owl species, all of which have high visual acuity and ability to distinguish colors in the visible light spectrum (Small et al. 1991, Höglund et al. 2019). While some species of predators hunt more nocturnally, all also exhibit crepuscular or diurnal hunting activity which coincide with times that grouse are most active (Hewitt and Kirkpatrick 1997, Passarotto et al. 2018).