Keep the Channel Islands Foxy

by: Mayra Concepcion

Urocyon littoralis

Four Subspecies of Island Fox (Urocyon littoralis) experienced catastrophic declines in the late 1990s, primarily due to golden eagle predation on the northern Channel Islands and canine distemper virus (CDV) outbreak on Santa Catalina Island (Timm et al. 2009).

In 2004, the FWS listed the San Miguel Island fox, Santa Rosa Island fox, Santa Cruz Island fox, and Santa Catalina Island fox as endangered (U.S. Fish and Wildlife Service 2004) pursuant to the ESA. The remaining two subspecies, the San Nicolas Island fox (U. l. dickeyi) and San Clemente Island fox (U. l. clementae), weren’t federally listed.

The IUCN (World Conservation Union) listed the entire species as Critically Endangered in 2001 (Sillero-Zubiri and Macdonald 2004). All six subspecies are listed as threatened by the State of California.

Recovery Plan Link

Island foxes feed on a wide variety of insect prey, native and introduced mice, small mammals, ground-nesting birds, and native plants. The island fox is a habitat generalist and an opportunistic omnivore; so, no critical habitat area was needed.

Although primarily nocturnal, the island fox is more diurnal than the mainland gray fox, possibly a result of historical absence of large predators and freedom from human harassment on the islands (Laughrin 1977).

The golden eagle is four times the size of the island fox and can easily prey on it.

Golden eagle predation has continued to be the primary mortality factor for foxes on the northern Channel Islands. The extirpation of bald eagles (Haliaeetus leucocephalus) from the Channel Islands as a result of dichlorodiphenyltrichloroethane (DDT) may have facilitated golden eagle colonization. Bald eagles historically bred on the islands and aggression by breeding bald eagles may have discouraged foraging golden eagles from establishing residence.

Successful longterm suppression of golden eagles would likely require removal of the non-native prey base (feral pigs removed from Santa Cruz Island and deer and elk removed from Santa Rosa Island), as well as the successful restoration of bald eagles to the northern Channel Islands (Coonan 2003; Coonan et al. 2005a).

Between November 1999 and July 2006, 44 golden eagles, were removed from Santa Cruz and Santa Rosa Islands (Latta et al. 2005; Coonan et al. 2010). They were trapped and subsequently released in northeastern California. The recent, successful restoration of bald eagles to the Channel Islands may also provide a deterrent to future golden eagle colonization of the islands. Sixty-one bald eagles were releasedon Santa Cruz Island as the result of annual experimental reintroductions of juvenile bald eagles from 2002 to 2006 (Coonan et al. 2010).

Captive breeding was conducted on each island and within 10 years, reproduction in the reintroduced wild populations was outpacing that in captivity.

The fox’s annual survival has remained relatively constant, at above 90 percent for most of period from 2004-2013. In 2013, however, island fox survival declined to about 80 percent, and five of the 11 mortalities that occurred in radio-collared foxes had evidence of a parasite never before recorded in island foxes (Coonan 2014). Necropsy of those foxes revealed acanthocephalans (spiny-headed worms).

Tracking population estimates for the total population (both adults and juveniles) reveals that it has hovered around 550 foxes since 2010, and this may very well represent carrying capacity for the island (Coonan 2014). This is supported by the general decline in reproductive effort as the population has increased.

Sources:
Recovery Plan
Foxy Image
Golden Eagle Image