Researchers, headed by Brian Cypher, examined the diet of island foxes across all six Channel Islands. Their findings have just been published in Global Ecology and Conservation, 2(2014) 255–66. Their article: “Multi-population comparison of resource exploitation by island foxes: Implications for conservation,” looks at the dietary differences between the six island subspecies, compares seasonal dietary shifts and dependence on introduced species, and recommends considerations for future conservation efforts. (Original paper)
The scientists gathered island fox scat across the six islands during four seasons in 2009. The scat samples were analyzed at California State University-Stanislaus’ Endangered Species Recovery Program office in Bakersfield, CA.
|San Miguel Island deer mouse, courtesy of C. Schwemm
- Animal Prey - island deer mice, birds, lizards, beetles and beetle larvae, Jerusalem crickets, silk-spinning sand crickets, and grasshoppers
- Plant Fruits - from toyon, manzanita, prickly pear cactus, and summer holly
- Introduced Species - earwigs, European snails, fruits of ice plant and Australian saltbush
|toyon fruit, courtesy of K. Dearborn animalbytes.net
Arthropods in the Diet
An interesting finding is the importance of numerous insect species. Insect parts constituted a “significant proportion of each scat.” The dark purple band in the graphic above depicts the frequency of insects found in scat on each island. On all six islands, beetles were a primary food item year-round (most identifiable were darkling beetles and ten-lined June beetles). Insect prey offers calorie-rich food for little energy expenditure, making them an efficient food source. In addition there was evidence island foxes occasionally ate cockroaches, dragonflies, butterfly caterpillars, and wasps.
European earwigs are now found across North America, including the Channel Islands. This introduced species has become an important food resource for island foxes. Earwigs were a primary food source on San Nicolas, San Miguel, Santa Rosa, and Santa Cruz, and were an important food source on San Clemente in the spring and on Santa Catalina during the fall and winter.
Crustaceans–beach hoppers and various crabs–were occasionally found in scat, demonstrating that some island foxes search for food along shorelines. Introduced European garden snails are now found on several of the Channel Islands and island foxes have included them in their foraging. On the two islands, San Clemente and San Nicolas, garden snails (red band on graphic) have become a primary food resource for island foxes.
|island fox with 3 deer mice in jaws, courtesy NPS
Some additional prey animals were found occasionally in fox scat: Catalina California ground squirrels (only found on Catalina), scavenged seal or sea lion, spotted skunk (competitors on Santa Rosa and Santa Cruz), a few black rats, a house mouse, and a bat. While island foxes have been seen catching snakes, no evidence of snake remains was found in 2009.
Native Fruiting Plants
|Santa Cruz Island fox in tree searching for fruit
While fruit is an important part of the diet for most island foxes, there can be a great deal of difference in the species consumed between islands. The chart below shows the plant species found in the scat with a more than 10% frequency.
Removing introduced animal species from the islands has eliminated some carrion opportunities for island foxes. However, carrion of large introduced animals is not believed to have ever been a primary food source for these omnivorous canines.
Removing introduced non-native plant species is a major goal across the Channel Islands, but this study reveals an important caution. Island foxes are consuming introduced ice plant and the garden snails it harbors. Before invasive ice plant and Australian saltbush can be removed, native fruiting plants will need to be reestablished so that island foxes have enough resources to survive.
This study provides the first comprehensive look at island fox diet across the Channel Islands and through the seasons. However, it represents one year: 2009. Native plant resources fluctuate with annual weather. Climate change and drought are impacting native plants and fruit production. Have impacts to plant resources in 2013 and 2014 challenged survival for island foxes and their smaller prey, which are also dependent on plant foods? Have island foxes altered their diet in the face of drought? (Parasite threat from food source on San Miguel) Can conservation measures to restore the natural ecosystem be managed so that resources are not compromised for island foxes? And will island foxes expand their diet as their ecosystem is restored? Continued study of island fox diet is vital to informed conservation decision making.
Download the original Research Paper “Multi-population comparison of resource exploitation by island foxes: Implications for conservation”