Species at their southern range margin are often dispersed throughout fragmented populations where they experience less optimum conditions compared to their central range. Spruce Grouse (Falcipennis canadensis) are boreal forest obligates distributed throughout the Northern United States and Canada and reach their southeastern range extent in Maine. I resurveyed 18 Black Spruce (Picea mariana) – Tamarack (Larix laricina) stands on Mount Desert Island, Maine, to observe changes in Spruce Grouse occupancy and abundance between the early 1990s (Whitcomb et al. 1996) and present day. I conducted two rounds of call back surveys within each stand from April to May, 2017. I used iButton units to collect stand-level temperature and humidity data for a three-week period starting July 25th, at the 18 sites to examine relationships between these variables and stand occupancy. Single-season occupancy models predicted that Spruce Grouse would occupy 0.226 (±0.100 SE) of stands with a detection probability of 0.857 (±0.141 SE). I only found 7 individuals. I found that stands which remained occupied were larger ( = 82.8ha) than unoccupied stands ( = 14.0ha), however, there was limited statistical support for this difference. There was no relationship between average daily maximum temperature and average daily humidity per stand and Spruce Grouse occupancy. Stand occupancy decreased from 8 stands to 4 when compared to the Whitcomb et al. (1996) study, and the number of individuals observed decreased from 39 individuals in 1993 to 7 individuals in 2017. My results suggest that over a span of 25 years Spruce Grouse populations on Mount Desert Island have decreased. Potential reasons for decline include habitat loss to development and loss of horizontal cover within stands due to forest succession.
Gilbert, Christopher J., "Twenty-Five Years of Change in Spruce Grouse Occupancy at Their Southern Range Margin in Maine, USA" (2018). Honors College. 333.