Alternate drumming site use by Ruffed Grouse in central Pennsylvania

We report on the use of alternate drumming sites by male Ruffed Grouse (Bonasa umbellus) during 1976-1997 within activity centers in a managed and an unmanaged forest in central Pennsylvania. Density of drumming males ranged from 1.6-12.5 males/km(2) in the managed forest and from 1.7-7.6 males/km(2) in the unmanaged forest. The proportion of males that used alternate drumming sites within activity centers ranged from 2% to 44% and was positively correlated with drumming male density. The number of alternate sites used within activity centers also increased with density; males used up to five alternate sites during a high-density year. Distances between alternate drumming sites and primary sites were not correlated with density but were greater on the unmanaged forest. The spatial orientation of multiple alternate sites relative to the primary site within each activity center suggested the use of alternate sites was a directional response. The actual direction of the response was not consistent among activity centers in the study area indicating it was not a result of prevailing abiotic factors such as wind, climate, or geomorphology. Similarly the placement of alternate drumming sites was not directed toward nearest neighboring males. We discuss potential causes of the behavior, its adaptive significance, and implications to commonly used survey techniques for Puffed Grouse populations.