Bobcat distribution and abundance in a Northern California ecosystem

Background/Question/Methods

Conservation and land management decisions are often based on an understanding of the distribution, abundance, and habitat requirements of wildlife.  In particular, the long-term population trends of the bobcat (Lynx rufus) in Northern California have not been assessed in depth.  In this study, I examined the spatial distribution and abundance of bobcats over two separate surveys at Jasper Ridge Biological Preserve in Woodside, CA.  The first survey took place from 2006-2008 and the second in 2014-2015.  Bobcat abundance from a previous survey in 2006 to 2008 was compared to their abundance from 2014 to 2015.  In these years, 24 camera traps at 12 locations were used to estimate mammal species abundance.  Vegetation surveys were taken to quantify plant density and composition.  

Results/Conclusions

The relative abundance of bobcats has decreased substantially from the 2006-2008 survey to the 2014-2015 survey.  This may be due to several factors, including the recent drought, increased human activity and construction, the incidence of notoedric mange, and increased puma abundance. The drought could indirectly affect bobcats by altering vegetation and reducing prey abundance.  In both surveys, bobcats and their prey species exhibited crepuscular activity patterns, and bobcat occurrences were not found to vary by season.  In the 2006 to 2008 survey, the distribution of bobcats was not predicted by prey activity or canopy type.  Unexpectedly, in the most recent survey, they were most abundant in locations with fewer occurrences of prey.  This could indicate that at present, the abundance of their prey is decreasing, and the prey in areas they frequent are being consumed faster than they can reproduce.  In addition, in the 2014-2015 survey, human activity did not affect bobcat distribution, likely due to the temporal separation between the diurnal activity of humans and the crepuscular activity of bobcats.  Further research on the impacts of human activity, the recent drought, and notoedric mange are necessary, as well as continued camera trap monitoring of bobcats.