Coyotes and Mesopredators in the Coastal Wetland at Naval Base Ventura County, Point Mugu
CHAPTER 1 - SPATIAL AND TEMPORAL RELATIONSHIPS OF COYOTES, RACCOONS, AND OPOSSUMS IN A SOUTHERN CALIFORNIA WETLAND The reduction in abundance of large carnivores may result in increases in smaller body sized carnivores, which subsequently depredate avian nests. This is known as the “mesopredator release hypothesis” and the implications for management of predator communities are important, particularly when the survival of endangered avian species is a consideration. However, little research has been conducted on the relationships between coyotes, mesopredators, and nest success of shorebirds and seabirds. The ecosystem at Naval Base Ventura County Point Mugu (Point Mugu) presented a unique opportunity to examine the interspecific dynamics of carnivores and their potential effects on nesting birds. From 1998 to 2002, predator management activities at Naval Base Ventura County Point Mugu implemented control of mammalian predators, with particular emphasis on coyote reduction. The subsequent decline in coyote numbers may have led to an increase in mesopredators such as raccoons and opossums. In order to address the relative vulnerability of California least terns and western snowy plovers to predation, we determined the home range, spatial distribution, habitat use, and activity of coyotes, raccoons, and opossums across Point Mugu from April 2002 to August 2003. The mean minimum convex polygon (MCP) estimate of home range for six coyotes was 17.9 km2 and the mean 50% fixed kernel estimate was 1.6 km2. The mean MCP estimate for six raccoons was 5.38 km2 and the mean 50% fixed kernel estimate was 0.56 km2. The mean MCP estimate for 16 opossums was 0.78 km2 and the mean 50% fixed kernel estimate was 0.05 km2. No other mesopredators were trapped and radio collared. All six coyotes had a portion of their MCP and 50% fixed kernels exclusive to themselves. Habitat within the portion of the home range not overlapped by mesopredators was primarily characterized by agricultural land and chaparral. Five coyotes had a portion of their home range overlapped with two mesopredators of both species (raccoon and opossum). Marsh and transitional habitats were the principal habitat types found within the areas overlapped with both raccoons and opossums. Radio collared coyotes did not use habitat types in proportion to their availability within the MCP home ranges (P < 0.01), with three coyotes using beach habitat more than expected (P < 0.05). The use of habitat by radio collared raccoons differed from expected based on availability within the MCP home ranges (P < 0.001), with five of six raccoons using urban habitat more than expected (P < 0.05). Twelve of 16 opossums used habitats differently from expected based on availability within the MCP home ranges (P < 0.001), with transitional habitat used more than expected. Activity of coyotes varied significantly by time of day (P = 0.01) and season (P = 0.03). Activity was lowest during the midday period and peaked in the evening and late night periods. Coyotes were less active during the pre-dispersal and dispersal season (01 August to 31 December) than breeding (01 January to 15 March) and the pup rearing (01 May to 31 July) seasons. Previous studies have shown raccoons and opossums to be primarily nocturnal. Therefore, they were omitted from analysis of activity across diel period and season. Interspecific relationships of coyotes, raccoons, and opossums were inferred through spatial overlap of home ranges, distance between locations in overlap areas, and habitat use. Raccoons and opossums may not be using open habitats such as beach and marsh to minimize detection, direct competition, and predation by coyotes. Thus, the presence of coyotes within these open habitat types may exclude more specialized nest predators such as raccoons and opossums from predating endangered least terns and snowy plovers. CHAPTER 2 - COYOTE DIET IN COASTAL SOUTHERN CALIFORNIA Coyotes at Naval Base Ventura County Point Mugu located on the coast of southern California, consumed a large variety of foods, particularly during the pup-rearing season (May to August). Mammals were consumed at a high frequency of occurrence (98%) throughout the year, with rabbits and hares (Family Leporidae) being the most commonly identified prey (55%) in 120 scat samples. Birds occurred at a frequency above 45% only during pup-rearing season, which suggested that birds were probably taken when abundant and vulnerable (nesting females and juveniles). We could not rule out possible consumption of avian species of concern.