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).