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9 May 2019 Changes in Occupancy and Relative Abundance of a Southern Population of Spruce Grouse Based on a 25-year Resurvey
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Abstract

Marginal populations are often distributed throughout fragmented landscapes and experience less optimum conditions compared to central range populations. Falcipennis canadensis (Spruce Grouse) inhabit conifer-dominated forests distributed throughout the northern US and Canada, and reach their southeastern range extent in the northeastern US, including Maine. We resurveyed 18 forest stands on Mount Desert Island, ME, that were comprised of Picea mariana (Black Spruce) and Larix laricina (Tamarack) and which were originally surveyed during 1992–1993. Our goal was to observe changes in Spruce Grouse occupancy and abundance between the 1990s and the present (2017). We conducted repeated callback surveys to detect territorial male Spruce Grouse within each stand during spring 2017, using a systematic survey design that covered the entirety of each stand and replicated methods used during the 1990s. We documented 7 individual Spruce Grouse, including 6 males and a single female. Single-season occupancy models for 2017 predicted Spruce Grouse stand occupancy of 0.226 (±0.100 SE), with a survey-level detection probability for male Spruce Grouse of 0.857 (±0.141 SE). Stand occupancy decreased from 8 stands in 1992–1993 to 4 in 2017, a 50% decline in the proportion of stands occupied. Further, the total number of males observed decreased from 32 (average between 1992 and 1993) to only 6 during our study, a >80% decline in apparent abundance. Our results suggest Spruce Grouse populations on Mount Desert Island have decreased and may be at risk of local extinction.

Christopher Gilbert and Erik Blomberg "Changes in Occupancy and Relative Abundance of a Southern Population of Spruce Grouse Based on a 25-year Resurvey," Northeastern Naturalist 26(2), 275-286, (9 May 2019). https://doi.org/10.1656/045.026.0204
Published: 9 May 2019
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