The Island Fox
(Urocyon littorals)
by Amanda Bozin
Ecology
The Island
Fox (Urocyon littoralis) is a species endemic to six of
the eight California Channel Islands. Roughly the size of a house cat, the
Island Fox on average is twelve to thirteen inches tall and weighs only four to
five pounds, yet it is the largest native mammal to the Channel Islands. On the
Channel Islands the Island Fox has no natural predators, allowing them to be
active during the day unlike their mainland ancestors, the Gray Fox (nps.gov). Their
lack of competition and predation have also allowed the Island Fox to become a
habitat generalist, using all habitat types occurring on the Channel Islands.
Rocks, brush, log piles, and earthen burrows are all commonly used as den sites
for Island Foxes (iucnredlist.org).
Geographic and Population Changes
Historically the Island Fox has always
existed in low population densities; however, populations went under decline in
the 1990s. This decline was due to predation by Golden Eagles, which had become
the dominant breeder on the Islands after the populations of the Bald Eagle,
their competitor, declined. By 2000 populations of Island Foxes had declined to
fifteen individuals on San Miguel and Santa Rosa Islands, and less than eighty
individuals on Santa Cruz Island (nps.gov). In 2004 the
Island Fox was listed as endangered under the endangered Species Act by the
U.S. Fish and Wildlife Service due to devastating population declines(ecos.fws.gov).
Threats to Continued Existence
The population
decline of the Island Fox has mainly been due to the predation by Golden eagles
as well as the canine distemper virus. This virus spread amongst the Island
Foxes due to their small populations with low genetic diversity. Low genetic
diversity makes diseases and parasites a major threat to the Island Foxes’
existence. In addition to low genetic diversity, small populations of Island
Foxes causes the species to be more susceptible to stochastic events. Other
threats to the Island Fox include habitat degradation from grazing. On some of
the Channel Islands threats also include competition with feral cats, deer, and
pigs; and mortality from vehicle strikes (ecos.fws.gov).
Recovery Plan
The Island
Fox recovery plan includes actions to remove threats of predation and disease,
as well as manage captive island fox populations, and establish monitoring
strategies (iucnredlist.org). These recovery efforts began in 1999 and most have been completed.
Successful captive breeding programs helped re-establish larger populations of
the Island Fox. By 2008 wild breeding had outpaced captive breeding and all of
the Island Foxes have since been released from captivity.
The
recovery efforts also produced a vaccine against canine distemper virus. Today a majority of
the Island Foxes is vaccinated for canine distemper virus as well as rabies.
These vaccines have relieved the population decline.
Golden Eagles were the main threat
to the Island Fox, causing the relocation of the Golden Eagle from the Channel
Islands to mainland California. This process has been successful as the population
of the Golden Eagles on the Channel Islands decreased the population of the
Island Fox increased. Recovery efforts have been a success. The total
population has risen from less than 1,500 individuals in 2002 to more than 4,000
in 2011. Today the annual survival rates of the Island Fox are above 85% (ecos.fws.gov).
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