Spilogale gracilis amphiala
The island spotted skunk is endemic to the two largest California Channel Islands, Santa Cruz and Santa Rosa. Unlike the island fox and the island deer mouse, the island spotted skunk shows no little differentiation between the two islands as well as the mainland subspecies, suggesting recent colonization of the species. In recent times, the species was limited in numbers. However, island spotted skunk populations on both islands began increasing in the late 1990s, coincident with the decline in island foxes caused by golden eagle predation. As the only two terrestrial carnivores on the islands, skunks and foxes are natural competitors.
Quick and Cool Facts
- Island spotted skunks on the two islands differ only slightly, with those on Santa Rosa spotted skunk being slightly longer than those on Santa Cruz.
- Island spotted skunks are only about a third as large as their competitor, the island fox.
- They are more carnivorous than foxes, and more nocturnal. However, their diet became a little more omnivorous in the absence of the fox, during the late 1990s.
- Skunks may live only one to two years in the wild.
- Historically, skunks have been classified as a subfamily in the weasel family, the Mustelidae. Recent genetic data has resulted in skunks being reclassified into its own family, Spilogale.
The island spotted skunk can be identified by its complex pattern of white markings on a blackbackground consisting of four to six broken white stripes, a triangular white forehead patch, a series of shorter white stripes resembling spots, and white on part of the abdominal surface and tip of the tail.
It is distinguished from spotted skunk subspecies on the mainland by its shorter tail and less white abdominal coloration, slightly larger size, broader skull, and proportionately less white and blacker in the fur. Like the mainland subspecies, the island spotted skunks exhibit sexual size differences, with males averaging 28% larger than females. This skunk is considerably smaller than striped skunks on the mainland and has softer, glossier fur.
Channel Islands spotted skunks currently occur only on Santa Cruz and Santa RosaIslands where they are widely distributed. Spotted skunks occurred on San Miguel Island, probably until the late nineteenth century. Fossil material has been collected on San Miguel Island and a spotted skunk was reportedly collected from San Miguel Island sometime during the 1870s. However, there have been no records of skunks on San Miguel since then.
Spotted skunks on the Channel Islands show habitat preferences similar to those reportedfor the mainland subspecies. Based on radio telemetry studies, spotted skunks on Santa Cruz Island showed a preference for chaparral-grassland, open grassland, fennel-grassland, and ravines. On Santa Rosa Island, spotted skunks were found to be associated with rocky canyon slopes, cactus patches, chaparral, coastal sage scrub, open woodland, other scrub-grassland communities, and riparian habitat along streams. On both islands, the species has also been recorded in or under human dwellings and ranch outbuildings. The elevational range of the Channel Islands spotted skunk extends from sea level to approximately 2000 feet.
Channel Islands spotted skunks are nocturnal. Activity begins at dusk, peaks during the early evening, and continues intermittently until dawn. On Santa Cruz Island, spotted skunks nest in cavities, burrows, and other natural crevices, as they do on the mainland. Dens are constructed in roots and earth under shrubs, cavities in rocks, open grassy areas, road cuts, human-made structures, and trunks and roots of oaks. Individuals use several dens distributed throughout their home range; some dens are used by two or more individuals either sequentially, or for females, simultaneously.
Spotted skunks on the Channel Islands have similar diets as those reported on the mainland. Studies on Santa Cruz Island showed skunks to be carnivorous, consuming primarily island deer mice and insects along with occasional lizards. Jerusalem crickets were the most frequent prey, but other prey included grasshoppers, crickets, beetles, caterpillars, earwigs, and ants. Seasonally available fruits and berries were collected on Santa Cruz Island consisting of grapes, summer holly stems and berries.
In recent years skunks have begun preying on seabirds nesting in sea caves on Santa Cruz Island. Expansion of skunk foraging to sea caves is likely a result of their substantial population increase following decline of foxes.
The breeding season for spotted skunks on the islands is probably similar to spotted skunks on the mainland. Western spotted skunks mate in September and October, and following delayed implantation and a 210-310 day gestation, give birth in April and May to 2-6. Counts of three and five uterine scars were recorded from two skunks collected at Santa Cruz Island in September.
On Santa Cruz Island, California, in a 1994 study of 47 dens used by island spotted skunks, 29.8% were under shrubs, 21.3% in open grassland, 21.3% in cavities in rocks, 10.6% in road cuts, 10.6% under human structures, and 6.4% in cavities in roots and trunks of trees.
According to the IUCN Red List (2008), the Western Spotted Skunk is listed as Least Concern as they are widely distributed in a variety of habitats including human altered habitats. The species may be declining in parts of the United States but not at a rate fast enough to be threatened. In contrast, prior to the recent upswing in skunk numbers on the islands, the island spotted skunk was thought to be rare, and was listed as a Species of Special Concern by the state of California. when the Island Spotted Skunk had a small population and was not well-studied, the skunk that time was designated as a species of concern. However, recent surveys now show a remarkable recovery in the species. On Santa Rosa Island, skunks are marked and counted during annual population monitoring for island foxes, and as of 2011 there were approximately 3,000 skunks on Santa Rosa Island.
- Ecology of the Island Spotted Skunk
- Channel Islands Spotted Skunk
- ICUN Red List
- Coonan, T. J. and A. Guglielmino. 2012. Island fox recovery program: 2010 annual report. Natural Resource Report NPS/MEDN/NRR-2012/483. National Park Service, Fort Collins, Colorado