Zubir-09.qxd 5/13/04 11:37 AM Page 173 CHAPTER 9 Island foxes The evolution, behavioural ecology, and conservation of island foxes Gary W. Roemer A yearling, male Santa Cruz island fox just Urocyon littoralis santacruzae prior to dispersal © G. Roemer. The island fox is (Urocyon littoralis) endemic to the currently recognized as a distinct subspecies, and California Channel Islands, a continental archipel- both the hypothesized colonization scheme and the ago located off the coast of the southwestern United current taxonomic classification are supported by States. A descendent of the mainland gray fox morphological and genetic evidence. (U. cinereo argenteus), it is hypothesized that island An insular existence has had a profound influence foxes first colonized the three northern Channel on the evolution, ecology, and genetic structure of Islands (Santa Cruz, Santa Rosa, and San Miguel) by island foxes. A dwarf form of the gray fox, island chance over-water dispersal. Native Americans then foxes are the smallest canid in North America. transported foxes from these islands to three south- Compared to mainland canids of similar size, island ern Channel Islands (Santa Catalina, San Clemente, foxes have shorter dispersal distances (mean ϭ and San Nicolas). Each island fox population is 1.39 km, SD ϭ 1.26, range ϭ 0.16–3.58 km, n ϭ 8), Zubir-09.qxd 5/13/04 11:37 AM Page 174 174 Biology and conservation of wild canids a smaller average home range size (mean annual home nature would bring a handsome price. Limú, of the range ϭ 0.55 km2, SD ϭ 0.2, n ϭ 14) and higher Chumash Indians of Santa Cruz Island was about to population densities (2.4–15.9 foxes/km2). Although introduce an animal that the Gabrielino Indians of they are distributed as socially monogamous pairs, Santa Catalina Island had never seen. The Gabrielino island foxes are not completely monogamous. Extra- were about to meet the island fox. pair fertilizations (EPFs) accounted for 25% of all Although fictional, this scene may well depict how offspring whose parents were determined through island foxes colonized the southern most Channel paternity analysis. This relatively high rate of EPFs Islands, a continental archipelago located off the may be related to high population density and the coast of southern California, USA (Fig. 9.1). proximity of suitable partners other than social Archaeological, ethnographic, morphological, and mates. Finally, the genetic gradient among fox popu- genetic evidence support the contention that foxes lations appears steeper than mainland populations were brought to the southern Channel Islands (Santa suggesting that smaller dispersal distances on islands Catalina, San Clemente, and San Nicolas) by Native result in increased population structure. Americans between 2,200 and 5,200 YBP (Collins An insular existence coupled with small popula- 1991a,b, 1993; Wayne et al. 1991b; Vellanoweth tion size may have also increased the vulnerability of 1998). Native Americans of the Channel Islands har- the island fox to extinction. Over the past decade, vested foxes to make arrow-quivers, capes, and head- five of the six subspecies have declined and two are dresses from their pelts, they ceremonially buried extinct in the wild. Factors contributing to these foxes, conducted an Island Fox Dance and most likely declines include predation by golden eagles (Aquila kept foxes as pets or semi-domesticates (Collins chrysaetos), the introduction of canine distemper 1991b). Island foxes played a prominent role in the virus and predator control efforts aimed at control- ling foxes to protect an endangered bird. A multi- faceted conservation strategy that includes the N 50 km live-capture and removal of golden eagles, the vacci- Northern Channel Islands nation of foxes against canine distemper virus, the SMI Los Angeles eradication of feral herbivores and the captive prop- SRO SCZ California agation of island foxes is currently underway to avert the impending extinction of this endemic canid. SCA Southern Channel Islands SNI Introduction SCL The bow sliced through the calm waters of the bay and then quietly slid to a stop on the gently sloping Santa Cruz Island beach. Limú was glad the journey was half over. The Fraser Point crossing from Santa Cruz Island to this sheltered bay Central Valley at the west end of Santa Catalina Island had been rough. The swells were half as tall as his tamal was long, and more than once he had felt they would lose 20 km their cargo. Their safety was critical to the success Figure 9.1 Island foxes occur on the six largest California of his trading effort. He was sure they would fetch Channel Islands. The three northern islands are Santa Cruz a handsome price, perhaps a few steatite bowls, (SCZ), Santa Rosa (SRO), and San Miguel (SMI), and the soapstone cookware coveted by all the tribes of the three southern islands are Santa Catalina (SCA), San Channel Islands, or maybe several sea otter pelts. Clemente (SCL), and San Nicolas (SNI). The enlargement of Yes, indeed, he was sure these gentle creatures with Santa Cruz Island shows the relative placement and size their beautiful cinnamon, white and grey coats, their of two trapping grids, Fraser Point and Central Valley, which large hazel eyes, and their inquisitive and playful were used to capture island foxes. Zubir-09.qxd 5/13/04 11:37 AM Page 175 Island foxes 175 spiritual and personal lives of these island Americans. (Collins 1982; Moore and Collins 1995). Morphology Fossil evidence dates the arrival of foxes to the north- is so distinctive that each fox population can be dis- ern Channel Islands (Santa Cruz, Santa Rosa, and San tinguished from the other solely on osteological Miguel) much earlier, from 10,400 to 16,000 YBP (Orr traits. Using 29 cranial and mandibular characters 1968). Their actual colonization probably occurred measured from 2,207 island and gray fox specimens, between 18,000 and 40,000 years ago, when these Collins (1982, 1993) correctly classified 91% of all northern islands were joined into one large island island fox specimens to their island of origin. known as ‘Santarosae’ (Collins 1982, 1993; Johnson Insularity has also had a profound influence on 1983). At its closest, Santarosae was a mere 6 km from genetic diversity and the phylogeography of the the North American continent, having reached its island fox. Founder events, genetic drift, and selection maximum size 18,000–24,000 YBP. It is hypothesized have played significant roles reducing phenotypic that sometime during this period, mainland gray and genetic variation, and creating six genetically dis- foxes, the progenitor of the island fox, colonized tinct populations. Island foxes contain about 35% of Santarosae by chance over-water dispersal, by either the genetic variation observed in mainland grey foxes, swimming or by rafting on floating debris (Collins and the fox population on San Nicolas Island is one of 1982, 1993). As glaciers retreated and sea levels rose, the most genetically invariant wild populations Santarosae was subdivided into separate islands. Santa known (Table 9.1). Genotype profiles generated from Cruz Island was formed first, some 11,500 YBP. Sea lev- hypervariable minisatellite and microsatellite DNA els continued to rise separating the remaining land were identical for all foxes assayed from San Nicolas mass once again, approximately 9,500 YBP, to form (Gilbert et al. 1990; Goldstein et al. 1999). Of the five Santa Rosa and San Miguel Islands. Native Americans then colonized the Channel Islands 9,000–10,000 YBP, and after establishment of an extensive trade Table 9.1 Genetic diversity at 19 microsatellite loci in route, transported foxes to the southern islands. the island fox and a mainland California population of gray fox Alleles/ % The island syndrome Population n locus Polymorphic He HW-He In general, insular populations differ from their main- San Miguel 17.8 1.7 47.4 0.106 0.155 land counterparts in aspects of form, genetics, (0.8) (0.2) (0.045) (0.048) demography, and behaviour. They may be dwarfed or Santa Rosa 25.4 2.5 57.9 0.198 0.274 gigantic, they typically have lower levels of genetic (0.9) (0.4) (0.056) (0.065) diversity, occur at higher densities, have decreased Santa Cruz 22.4 2.3 57.9 0.209 0.284 dispersal tendencies, and reduced aggression (Stamps (1.1) (0.3) (0.047) (0.058) and Buechner 1985; Adler and Levins 1994; Burness San Nicolas 26.4 1.0 0 0 0 et al. 2001). Island foxes are no exception. A dwarf (0.9) (0.0) (0.0) (0.0) form of the mainland gray fox, island foxes are the San Clemente 24.9 2.1 52.6 0.228 0.248 smallest North American canid, varying in body mass (1.1) (0.3) (0.061) (0.064) from 1.4 to 2.5 kg, roughly two-thirds the size of a Santa Catalina 25.4 2.5 89.5 0.341 0.405 mainland grey fox (Moore and Collins 1995; Roemer (1.1) (0.2) (0.046) (0.043) et al. in press). Further, each insular population differs Grey fox 11.9 6.3 94.7 0.700 0.752 in body mass and morphology (Collins 1982, 1993; (0.6) (0.5) (0.045) (0.047) Wayne et al. 1991; Roemer et al. in press). For example, Santa Catalina has the largest island foxes (U. littoralis Note: The San Nicolas island fox population is genetically invariant at all catalinae), San Clemente’s foxes (U. littoralis clementae) loci. n: mean sample size per locus (ϮSD); Alleles/locus: mean number have the smallest craniums and San Miguel foxes of alleles per locus; % Polymorphic: the percentage of loci that had two or (U.