Conservation Status
A decline in island fox populations was identified in the 1990s. On San Miguel Island the decline began in 1994, the adult population falling from 450 to 15 in 1999. Similar population declines were discovered on Santa Cruz Island, where the population decreased from 2,000 adults in 1994 to less than 135 in 2000, and on Santa Rosa Island where foxes may have numbered more than 1,500 in 1994 but were reduced to 14 animals by 2000. Golden eagle predation, discovered when foxes were radio-collared and monitored, proved to be the cause of the high mortality rates.
Golden eagle predation is the primary cause of island fox mortality. The golden eagle was an uncommon visitor to the Channel Islands before the 1990s according to data gathered by Dr. Lyndal Laughrin of the University of California Santa Cruz Island Reserve, and the first golden eagle nest was recorded on Santa Cruz Island in 1999. Biologists propose that the eagle may have been attracted to the islands in the 1960s after the decline of the bald eagle. The golden eagle replaced the bald eagle and began to feed on feral pigs due to the decimation of the local bald eagle population due to DDT exposure in the 1950s—the bald eagle would have deterred the golden eagle from settling on the islands while it subsisted on fish.
The feral pigs on Santa Rosa were exterminated by the National Park Service in the early 1990s which removed one of the golden eagle's food sources. The golden eagle then began to prey on the island fox population. Feral pigs on Santa Cruz Island and introduced deer and elk on Santa Rosa Island were introduced almost seventy years prior to island fox decline, therefore, the golden eagle most likely did not seek these animals as alternative prey. This has occurred most likely as a result of a process known as 'apparent competition'. In this process, a predator, like the golden eagle, feeds on at least two prey, for example, the island fox and feral pigs. One prey item is adapted to high predation pressure and supports the predator population (i.e. pigs), whereas the other prey item (i.e. the island fox) is poorly adapted to predation and declines as a consequence of the predation pressure. It has also been proposed that complete removal of golden eagles may be the only action that could save three subspecies of the island fox from extinction.
Introduced diseases or parasites can devastate island fox populations. Because the island fox is isolated, it has no immunity to parasites and diseases brought in from the mainland and are especially vulnerable to those the domestic dog may carry. A canine distemper outbreak in 1998 killed approximately 90% of Santa Catalina Island's fox population. After several years of carefully trapping the foxes and vaccinating them against distemper and rabies, their population has reached 1,542, surpassing the population of about 1,300 seen before the animals were ravaged by the disease that scientists believe was introduced by a pet dog or a raccoon from the mainland that hitched a ride on a boat or a barge.
Diminished food supply and general degradation of the habitat due to introduced mammal species, including feral cats, pigs, sheep, goats, and American bison, the latter having been introduced to Catalina Island in the 1920s by a Hollywood film crew shooting a Western, also has had a negative effect on fox populations.
The foxes threaten a population of the severely endangered loggerhead shrike in residence on San Clemente Island. The island fox population on San Clemente Island has been negatively affected by trapping and removal or euthanasia of foxes by the United States Navy. Since 2000, the Navy has employed different management strategies: trapping and holding foxes during the shrike breeding season, the installation of an electric fence system around shrike habitats, and the use of shock collar systems. With the gradual recovery of the shrike population on San Clemente Island, the Navy no longer controls the foxes. Automobile fatalities have also been high on San Clemente, San Nicolas, and Santa Catalina Islands.
Read more about this topic: Island Fox
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