COS 50-8 - Home ranges and group sizes of tule elk at Point Reyes National Seashore, California

Wednesday, August 5, 2009: 10:30 AM
Taos, Albuquerque Convention Center
McCrea A. Cobb and Reginald H Barrett, Environmental Science, Policy, and Management, UC Berkeley, Berkeley, CA

The tule elk (Cervus elaphus nanodes) is a formerly threatened species that was reintroduced to Point Reyes National Seashore (PORE), California in 1978.  Three distinct herds of tule elk now exist at PORE: a high-density, fenced population inhabiting designated wilderness; a low-density, open population inhabiting designated wilderness habitat; and a low-density population found on actively managed ranchland. This unusual situation allows an examination of potential differences in space usage and grouping behavior among adjacent elk populations at different densities and with varied available habitat.  Between 2005 and 2007, 42 adult female tule elk were fitted with radio telemetry and GPS collars, and were relocated approximately 2-times per week.  Visual group counts and classifications by age and sex were attempted on all relocated elk groups containing radio-collared elk.  Herd membership for individual radio-collared elk within populations was calculating using a coefficient of association.  We compared seasonal and annual group size and sex/age classification between herds at PORE.  Kernel home ranges and core areas were created in a GIS.  We examined the relationship between home range sizes, group sizes and herd densities (elk per hectare grassland) at annual and seasonal scales using regression analysis. 


Coefficients of association provided evidence for 6 distinct elk herds at PORE.  We discovered high levels of cohesion between radio-collared elk within herds, and little association with neighboring elk over the 3-year period.  Mean annual home range sizes varied dramatically among herds, from 85 hectares to 661 hectares.  Mean group sizes varied seasonally, and were approximately twice as large during the winter period compared to the summer period.  We found a strong negative relationship between the number of elk per hectare of grassland and annual elk home range size. Overall, the results from this study indicate that higher elk herd densities relate to smaller elk home ranges and group sizes at PORE.

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