Reproductive Ecology of Sharp-Tailed Grouse on the Pine Barrens of Northwestern Wisconsin

Abstract

Sharp-tailed grouse were once abundant throughout Wisconsin, but only a few isolated populations presently exist due to the loss of early successional habitat they require. Most populations are found on savanna reserves managed for sharp-tailed grouse or recent large clearcut areas of industrial and public forestland in the northwestern part of the state. Populations on large clearcuts are of high numbers and densities, but on some managed savanna reserves numbers and densities are low. I studied nesting success, hen survival, chick survival and production, and vegetation and habitat characteristics associated with nest site selection and nesting success on 6 study sites in northwestern Wisconsin. Study sites were classified as a managed landscape or unmanaged landscape. Nesting success (P = 0.015) and hen survival during the reproductive period (P = 0.035) and entire study period (P = 0.045) were significantly greater on unmanaged landscapes than managed landscapes. Chick survival (P = 0.11) and production (P = 0.47) were not significantly different between landscape types. Predation of brood hens accounted for the loss of most broods on managed landscapes, but adverse weather during the early brood period was suspected as the primary cause of brood losses on unmanaged landscapes. Large clearcut areas in northwestern Wisconsin may have higher numbers and densities of sharp-tailed grouse than managed savanna reserves due to higher nesting success and hen survival. Vegetation and habitat characteristics were examined at 3 scales: landscape, small scale, and microhabitat. On managed landscapes, hens preferred adjacent clearcut areas for nesting habitat to managed savanna reserves (P = 0.001). Hens selected nest sites in areas with greater fragmentation (P = 0.014) and further from tall trees (P = 0.001) at the landscape scale. Coniferous tree cover (P = 0.043), heath-type cover (P = 0.010), and deciduous woody cover (P = 0.016) were positively correlated with nest site selection at the small scale, and forb cover (P = 0.078) and non-woody and heath-type vegetation height (P = 0.011) were negatively correlated. Microhabitat vegetation characteristics positively associated with nest site selection were grass cover at the nest bowl (P = 0.007), coniferous tree cover (P = 0.021), heath-type cover (P = 0.091), and deciduous woody cover (P = 0.016). Grass cover near the nest (P = 0.049) and woody vegetation height (P = 0.017) were negatively correlated with nest site selection. Hens on unmanaged landscapes selected nest sites in areas of lower fragmentation (P = 0.002) and closer to forest edges (P = 0.013) at the landscape scale. Raspberry cover (P = 0.003) and heath-type cover (P = 0.017) positively influenced nest site selection at the small scale, but forb cover (P = 0.014) and non-woody and heath-type vegetation height (P < 0.001) were negative influences. Grass cover (P = 0.015) and grass height (P = 0.002) at the nest bowl, coniferous tree cover (P = 0.003), visual obstruction measurements (P = 0.018) and height of non-woody and heath-type vegetation (P = 0.013) were microhabitat vegetation characteristics positively associated with nest site selection. Grass cover (P = 0.031) near the nest was negatively correlated with nest site selection. On managed landscapes, nests nearer to tall trees (P = 0.074) were less successful. At the microhabitat scale, deciduous woody cover (P = 0.057), and grass cover (P = 0.092) near nests were negatively correlated with nesting success. Height of non-woody and heath-type vegetation (P = 0.079) at the small scale was negatively correlated with nesting success on unmanaged landscapes. Nesting success was significantly greater on unmanaged landscapes than managed landscapes, but was not different between adjacent clearcut areas and managed savanna reserves on managed landscapes (P = 0.78). Fragmentation at the landscape scale may influence nesting success through nest site selection, and woody vegetation may influence nesting success on managed landscapes through nest density and distribution. Lengthening prescribed burning rotations on managed landscapes may increase preferred nesting habitat and nesting success on managed landscapes, but landscape scale management utilizing clearcut habitat is necessary to maintain populations of sharp-tailed grouse into Wisconsin's future.