Recovering the Island Fox: Eagles, Diseases, Exotics, Oh My!

Recovering the Island Fox: Eagles, Diseases, Exotics, Oh My!

By Rhys Gilmore

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The island fox, Urocyon littoralis, is endemic to six of the eight California Channel Islands and can be found nowhere else on the planet.  At only a foot in height and merely three to six pounds in weight, the species is one of the smallest fox species in the world. The most probable explanation for the foxes’ existence implies the species is a descendant of the mainland gray fox.  Approximately ten thousand years ago during the ice age, gray foxes likely found their way to Santarosae, a massive island that later split into the northern Channel Islands.  The gray foxes then evolved to create the significantly smaller island fox species.

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As Earth warmed at the end of the Ice Age, sea levels rose and Santarosae became the four northernmost Channel Islands.  Thousands of years of geographic isolation caused the island fox to develop six distinct subspecies, corresponding to each island it inhabits.  By 1994, four of these six subspecies experienced catastrophic population declines.  In the most extreme case, on Santa Rosa Island, the population decreased by 99.2%

Island Subspecies	Initial Population	Population after Decline
San Miguel	450	15
Santa Rosa	1750	14
Santa Cruz	1450	55
Santa Catalina	1300	103

A draft recovery plan for the four subspecies listed in the table above emerged in May 2012.  Since then, recovery efforts have been primarily successful—the species has been de-listed and is no longer considered a threatened or endangered species.

There were numerous causes of the island fox’s imperilment including exotic species, diseases, and toxin exposure.  Habitat degradation due to exotic grazers along with low genetic diversity and diseases such as the Canine Distemper Virus thwarted the survival of the island foxes.  However, the introduction of golden eagles to the island was by far the most threatening exposure to island fox survival.  After World War II, the use of the pesticide DDT caused the extinction of the bald eagles on the Channel Islands. The absence of the bald eagle and later introduction of large grazers, such as pigs and deer attracted golden eagles from the mainland.  Island foxes have no natural predators and are approximately a fourth the size of golden eagles.  Consequently, by the 1990s, golden eagles had nearly brought about the extinction of island foxes.

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The recovery of the island fox is largely dependent on the elimination of the main threats to the species, golden eagles and disease, and maintaining and monitoring the current populations.  In 2004 the species was listed under the Endangered Species Act of 1973.  Since then, the species has recovered substantially due to a multitude of factors.  The surviving island foxes were frst brought into captivity where captive breeding helped ensure population growth.  Meanwhile, golden eagles were captured and moved from the Channel Islands to Northern California.  Exotic plant species and grazers have also been removed—however this is a work in progress.  Bald Eagles, which prey on fish, have since been introduced with the hope of deterring golden eagles from returning.  The island fox population is also extensively monitored with tracking microchips and collars.  Foxes are vaccinated as threatening diseases are identified.  Although drought in recent years has negatively affected the foxes, the recovery plan is largely viewed as a success—the island fox is no longer listed as a threatened or endangered species.

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Sources:

http://www.nps.gov/chis/learn/nature/island-fox.htm

http://www.iucnredlist.org/details/22781/0

http://www1.islandfox.org/p/about-island-fox.html