Does availability of anthropogenic food enhance densities of omnivorous mammals? An example with coyotes in southern California

Abstract

To evaluate whether the abundance of coyotes Canis latrans was influenced by the availability of anthropogenic foods in a humanized landscape, we compared three neighboring areas (hereafter referred to as NA, CA, and SA) under contrasting human pressures within the Santa Monica Mountains of California, USA. We quantified the use of anthropogenic foods by coyotes and assessed local densities within these three regions. Overall, 761 coyote feces were analyzed; identified food items were categorized into 11 food types (7 native and 4 anthropogenic). Though small mammals (lagomorphs and rodents) were the main prey of coyotes in all areas and seasons, log-linear modeling of multiway contingency tables indicates that consumption of anthropogenic foods by coyotes varied significantly throughout study areas. Thus, in the most humanized area (CA; 24% of this region is residential habitat), anthropogenic foods (trash, livestock, domestic fruit) comprised seasonally between 14 and 25% of total items in coyote diets, whereas in the least humanized area (NA; 2% residential) anthropogenic foods only comprised seasonally between 0 and 3% of items. Coyote density, estimated by foot-hold trapping surveys and by genotyping feces, was also highly variable between areas. The heavily human-impacted CA area had the highest coyote density (2.4-3.0 ind. km-2), whereas coyote density was significantly lower (0.3-0.4 ind. km-2) in the least humanized area (NA). In the third region (SA; 10% residential), with an intermediate level of human pressure, both importance of anthropogenic foods in coyote diet (4-6%) and coyote density (1.6-2.0 ind. km-2) were intermediate compared to the other regions. Our data suggest that subsidization by anthropogenic foods augments coyote densities and alters their diets in the Santa Monica Mountains, California. We include data from literature to show that anthropogenic foods are used by omnivorous mammals throughout the world. Surprisingly, however, the potential effects of allochthonous inputs on such species are not well-understood. Thus, further research on this phenomenon in humanized landscapes is needed.