Abundance and distribution of ruffed grouse Bonasa umbellus at the southern periphery of the range

Abstract

Peripheral populations of ruffed grouse Bonasa umbellus at the trailing edge of their range are likely to be at risk of population declines and potential extirpation from continued climate and habitat change. Accurate estimates of abundance and distribution are needed for peripheral populations to inform management decisions. We show that ruffed grouse density at the southern periphery of their range is much lower than in areas farther north. We surveyed the abundance of drumming male grouse across northern Georgia during the springs of 2020–2021 by performing roadside point counts at 634 survey points. We used hierarchical distance sampling models to predict grouse abundance across north Georgia and model spatial variation in density. We estimated population size to be 2671 ruffed grouse in Georgia (95% confidence interval 678–11 084). Mean grouse density was 0.003 drumming males/ha (SD = 0.006), with the highest density centered in the high-elevation mountains. Uncertainty around abundance estimates was high, in part due to low precision when estimating availability. Low detectability and precision are likely to be common issues when surveying low-abundance populations, as often occurs at range peripheries. We suggest that abundance estimation could be improved by integrating alternate methods, such as automated recording units, into existing monitoring protocols.