Origins and antiquity of the island fox (Urocyon littoralis) on California’s Channel Islands
Torben C. Rick, Jon M. Erlandson, René L. Vellanoweth, Todd J. Braje, Paul W. Collins, Daniel A. Guthrie, and Thomas W. Stafford Jr. 2009. Origins and antiquity of the island fox (Urocyon littoralis) on California’s Channel Islands. Quaternary Research 71 (2009) 93–98.
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Abstract
The island fox (Urocyon littoralis) is one of few reportedly endemic terrestrial mammals on California’s Channel Islands. Questions remain about how and when foxes first colonized the islands, with researchers speculating on a natural, human-assisted, or combined dispersal during the late Pleistocene and/or Holocene. A natural dispersal of foxes to the northern Channel Islands has been supported by reports of a few fox bones from late Pleistocene paleontological localities. Direct AMS 14C dating of these “fossil” fox bones produced dates ranging from ~6400 to 200 cal yr BP, however, postdating human colonization of the islands by several millennia. Although one of these specimens is the earliest securely dated fox from the islands, these new data support the hypothesis that Native Americans introduced foxes to all the Channel Islands in the early to middle Holocene. However, a natural dispersal for the original island colonization cannot be ruled out until further paleontological, archaeological, and genetic studies (especially aDNA [ancient DNA]) are conducted.
Introduction
The endangered island fox (Urocyon littoralis), a diminutive relative of the gray fox (U. cinereoargenteus), has been an important apex predator on California’s Channel Islands for millennia (Collins, 1993; Moore and Collins, 1995; Roemer et al., 2004). While a great deal is known about island fox ecology, biogeography, and conservation, questions remain about when and how these animals first colonized the Channel Islands (Johnson, 1975, 1983;Wenner and Johnson, 1980; Collins, 1991a; Vellanoweth, 1998; Agenbroad, 2002a). Most researchers agree that Native Americans introduced the island fox to the southern Channel Islands, probably during the middle to late Holocene (Collins, 1991a,b; Vellanoweth, 1998; Shelley, 2001). Based partly on reports of fox remains from late Pleistocene sediments of the Upper Tecolote Formation on Santa Rosa Island, however, foxes were thought to have reached the northern Channel Islands naturally during the late Pleistocene by rafting across a Santa Barbara Channel narrowed by lower sea levels (Wenner and Johnson, 1980; Collins, 1991a,b, 1993).
Recent AMS (Accelerator Mass Spectrometry) 14C dating of the Upper Tecolote Formation fox specimen to the late Holocene raised questions about the natural dispersal of foxes to the northern islands (Shelley, 2001), but several fox bones from San Miguel Island fossil localities continued to support a possible Pleistocene age for the origins of the island fox (Guthrie, 1993:409). All the San Miguel specimens were found on eroded surfaces where faunal remains of paleontological, archaeological, or recent biological origin could have become mixed.
To help clarify the origins, antiquity, and evolution of island foxes, we obtained direct AMS 14C dates for three island fox bones from the late Pleistocene San Miguel Island fossil localities (Fig.1). These are the only known specimens that could predate the earliest definitive evidence for human colonization of the northern Channel Islands, approximately 13,000 cal yr BP (Johnson et al., 2002).
Context and background
Divided into northern (Anacapa, Santa Cruz, Santa Rosa, and San Miguel) and southern (San Clemente, Santa Catalina, San Nicolas, and Santa Barbara) groups, California’s eight Channel Islands range in size from about 2.6–249 km2. Currently between 20–98 km offshore, the islands have not been connected to the mainland during the Quaternary (Johnson, 1983). During glacial periods of the Pleistocene, lower sea levels caused the northern islands to coalesce into a single, larger island (Santarosae), the eastern end of which was only 6–8 km from the mainland (see Porcasi et al., 1999; Kennett et al., 2008). Considerably more dispersed and isolated, the southern islands have remained farther from the mainland and were more difficult for terrestrial animals to colonize.
Island foxes are about the size of a house cat (Fig. 2), with subspecies found on all the islands except Anacapa and Santa Barbara (each ~2.6–3 km2 in area). Other endemic island terrestrial mammals appear to have been limited primarily to the deer mouse (Peromyscus maniculatus), western spotted skunk (Spilogale gracilis), western harvest mouse (Reithrodontomys megalotis), San Miguel Island vole (Microtus miguelensis), and ornate shrew (Sorex ornatus) (Guthrie, 1998; Schoenherr et al., 1999). Pygmy (Mammuthus exilis) and fullsized (M. columbi) mammoths lived on the northern islands during the Pleistocene (Agenbroad, 1998; Thaler, 1998). Mammoths are generally good swimmers that colonized the islands naturally, while foxes are poor over-water dispersers (Wenner and Johnson, 1980; Johnson, 1983; Collins, 1991a).
The focus of extensive conservation, including a captive breeding program, four subspecies of island fox are currently critically endangered due to predation by golden eagles (Aquila chrysaetos) and possibly canine diseases (Coonan et al., 2002, 2005; Roemer et al., 2002, 2004; Clifford et al., 2006). Foxes are omnivorous, consuming insects, fruits, mice, small reptiles, marine invertebrates, and other foods, and they prey on deer mice and ground nesting birds (Moore and Collins, 1995). Island foxes are generally docile, show little fear of humans, and are easily tamed (Moore and Collins, 1995).
Island foxes played an important role in the spiritual lives of native Channel Island peoples—the Island Chumash and Tongva (Gabrielino). Island foxes have been found in numerous archaeological sites, were likely semi-domesticates or pets, were harvested for their pelts, and probably served other functions like pest/rodent control (Collins, 1991b). The Chumash and Tongva had extensive exchange networks with the mainland and islands, including trade of a variety of beads, subsistence items, other goods, and likely island foxes (Collins, 1991b; Vellanoweth, 2001; Kennett, 2005). …
Results
Calibrated 14C dates for the three island fox specimens range from ca. 6400 cal yr BP to the Historic period—much younger than the late Pleistocene dates available for other bones from the same localities (Table 1). The locality V-7 ulna produced a date of 6120±25 14C yr BP (6400–6210 cal yr BP; UCIAMS-40173), currently the oldest securely dated fox from the Channel Islands. …
AMS measured d13C values were also obtained for the three San Miguel Island fox specimens, with the preliminary values ranging from -11.6‰ for the ca. 6400 yr old specimen to -18.4‰ and -19.5‰ for the two late Holocene specimens. …
Discussion
Prior to our study, several researchers speculated that island foxes evolved from gray foxes that arrived on the northern islands by chance-rafting during the Pleistocene, with Native Americans later transporting island foxes to the southern islands (Wenner and Johnson, 1980; Collins, 1991a; Vellanoweth, 1998). Others speculated on human-assisted dispersal of foxes to all the islands (Vellanoweth, 1998; Kennett, 2005:49). Through analysis of island fox and mainland gray fox skeletons, Collins (1991a, 1993) suggested that gray foxes may have first colonized the islands just prior to the Wisconsin glaciation (~25,000 14C yr BP), and under selective pressure and inbreeding rapidly dwarfed into the small-sized island fox in 10,000 yr or less. …
Numerous paleontological projects … have yielded faunal assemblages that include abundant avian materials, extant and extinct micro-mammals, reptiles and amphibians, and mammoths (Guthrie, 1980, 1993; Walker, 1980; Agenbroad, 1998). Orr (1968) estimated that a minimum of 200 mammoths had been identified by the early 1960s. Agenbroad’s (1998, 2002b) surveys on Santa Rosa, San Miguel, and Santa Cruz identified over 140 new mammoth localities.
In contrast, island foxes are rare or absent in fossil deposits and the few that have been found are all Holocene in age. Moreover, at Daisy Cave, pre-human deposits lack island foxes, yet post-human archaeological deposits contain them (Walker, 1980). If island foxes originated from a small founding population prior to human arrival, finding the remains of those presumably full-sized foxes in the fossil or archaeological records would be difficult. However, the complete absence of island foxes in pre-human age deposits is peculiar, especially given the large samples of birds, micromammals, and mammoths that have been recovered in Quaternary deposits. …
Conclusions
Foxes and domestic dogs were present on California’s Channel Islands since at least the middle Holocene, and their introduction by humans would have significantly altered island ecosystems. The purportedly pre-human-age island fox bones have now been directly 14C dated to the Holocene, with island foxes on the northern islands for at least 6400 yr and on the southern islands (San Nicolas) for at least 6000–5000 yr (Vellanoweth, 1998; Shelley, 2001). Several lines of evidence support the hypothesis that Native Americans introduced foxes to all the islands where they are currently found, including: 1) the widespread occurrence of foxes in island archaeological sites and absence in pre-Holocene fossil/subfossil deposits; 2) deliberate translocation of foxes between islands by Native Americans; 3) significance of foxes in Native American religion and ceremony; 4) presence of late Pleistocene ground nesting colonies of Chendytes and Fratercula; and 5) rapid dwarfing of animals on other islands around the world.
This is one of the few known animal translocations by hunter-gatherers (see Grayson, 2001) and demonstrates a significant Native American influence on the structure and functioning of Channel Island ecosystems. …
