The island fox (Urocyon littoralis) is endemic to the California Channel Islands. Over the past thirty years the species experienced a dramatic population decline to near extinction followed by rapid recovery. These drastic fluctuations in population size make the island fox an excellent candidate for studying the effects of density on home range size and habitat selection. In 2010, when density was historically low, researchers on Santa Rosa Island used GPS collars to document male fox home ranges on the eastern portion of the island. Beginning in 2022, with the fox population now at carrying capacity, we tracked the locations of 15 adult male foxes using GPS collars in a similar study area to compare their home range size, characteristics and overlap. Preliminarily, we have found that island foxes display density dependent effects on home range size. Fox home ranges were significantly smaller at higher population density. We also found that island foxes exhibit minimal home range overlap regardless of population density. Due to the inability of island species to disperse as their population increases, understanding density dependent effects on island fox home ranges is especially important for informing management decisions for this iconic species.

The island spotted skunk (Spilogale gracilis amphiala) is a rare, cryptic mesocarnivores endemic to Santa Rosa and Santa Cruz Islands, part of the California Channel Island archipelago. During the near-extinction of the sympatric island fox via predation by invasive golden eagles, island spotted skunk populations increased significantly. Now island foxes have recovered on these islands and skunks seem to have precipitously declined - potentially due to interspecific competition with foxes, who have a larger body size and broader temporal and dietary niche. We suspect that skunks now have low abundance on both islands. We are investigating island-wide occupancy via year-round camera surveys on both islands, with cameras placed in drainages to maximize detectability of this small mesocarnivore. We installed 92 cameras in the summer of 2023 and will maintain them for one year. Preliminary data suggests that skunks have low rates of occupancy across both islands, and differential rates of occupancy are associated with topographic, environmental, and interspecific interaction-level differences across sites. This study helps address a time-sensitive question of how island spotted skunk populations are responding to high fox abundance, and could be used to inform future studies, conservation, and management on the Channel Islands.

Island species have long been considered an important system for investigating evolutionary forces leading to divergence. The Island spotted skunk (Spilogale gracilis amphiala) is an endemic insular carnivore found on two of the California Channel Islands: Santa Rosa Island and Santa Cruz Island. Limited study of morphology found little differentiation between the island spotted skunks and their mainland counterpart, the western spotted skunk (S. gracilis spp.), leading some to suggest that spotted skunks may have arrived on the Channel Islands <200 years ago. However, studies using microsatellite and mitochondrial markers found significant differences among the two island populations and mainland populations. Still, these markers were insufficient to precisely estimate when island skunks diverged from one another and their mainland relative. To address this question as well as consequences for genetic diversity and inbreeding, we used a combination of whole genome sequencing on six individuals and reduced representation sequencing on 72 individuals. We estimated genomic diversity, inbreeding, and timing of population divergence. Our results support the antiquity of island spotted skunks, showing high genomic differentiation among all three populations, and both lower diversity and increased inbreeding in island populations. Additionally, demographic trajectories of island and mainland populations diverged >10,000 years ago.

Currently, 17 of the 26 bat species now known to occur in California have been identified by capture, sightings, or acoustic records on the eight California Channel Islands. Of these only six species are known to breed on the islands. On Santa Cruz Island, breeding Yuma myotis (Myotis yumanensis) were documented in 2017 and a lactating long-legged myotis (M. volans) was captured in 2022, the latter a first for all the Channel Islands. In 2017 and again in 2018, we captured juvenile red bats on Santa Cruz Island indicating local breeding. Valdez and Haidar (pers.comm.) identified the 2018 capture by total genomic analysis as an eastern red bat (Lasiurus borealis), a new record of this species for California. Some call frequencies of eastern and western red bats (L. frantzii) overlap, however we infer that both species have been acoustically recorded on Santa Cruz, Santa Catalina and San Nicolas Islands. Between 2017 and 2022, long-term acoustic recording stations have been installed on Santa Cruz (Brown and Rainey); Santa Catalina (Santa Catalina Conservancy); San Nicolas (USN and USGS); and San Clemente, Anacapa and Santa Rosa Islands (USGS). Acoustic data have documented new species for all the islands, and several new records on individual islands.