Diet of a threatened endemic fox reveals variation in sandy beach resource use on California Channel Islands

The coastal zone provides foraging opportunities for insular populations of terrestrial mammals, allowing for expanded habitat use, increased dietary breadth, and locally higher population densities. We examined the use of sandy beach resources by the threatened island fox (Urocyon littoralis) on the California Channel Islands using scat analysis, surveys of potential prey, beach habitat attributes, and stable isotope analysis. Consumption of beach invertebrates, primarily intertidal talitrid amphipods (Megalorchestia spp.) by island fox varied with abundance of these prey across sites. Distance-based linear modeling revealed that abundance of giant kelp (Macrocystis pyrifera) wrack, rather than beach physical attributes, explained the largest amount of variation in talitrid amphipod abundance and biomass across beaches. delta C-13 and delta N-15 values of fox whisker (vibrissae) segments suggested individualism in diet, with generally low delta C-13 and delta N-15 values of some foxes consistent with specializing on primarily terrestrial foods, contrasting with the higher isotope values of other individuals that suggested a sustained use of sandy beach resources, the importance of which varied over time. Abundant allochthonous marine resources on beaches, including inputs of giant kelp, may expand habitat use and diet breadth of the island fox, increasing population resilience during declines in terrestrial resources associated with climate variability and long-term climate change.

Automated summary

The study found that island foxes on the California Channel Islands utilize sandy beach resources to expand habitat and dietary options, with stable isotope analysis showing individual differences in diet. Abundant marine resources on coastal beaches may increase population resilience of island foxes, especially during declines in terrestrial resources due to climate variability and long-term climate change.