Island Fox

How do we bring the endemic island fox back from the brink of extinction?

Island fox puppies being socialized in the captive pens, prior to being released into the wild after the successful removal of non-native feral pigs, and golden eagles from Santa Cruz Island, 2006. Photo: © Christina Boser/TNC

Island foxes evolved on the California Channel Islands, a chain of eight islands located off the coast of southern California. In the late 1990s, the foxes on Santa Cruz Island and its neighbor islands to the west, started to decline rapidly. Research revealed that this was due to predation by golden eagles which had been spotted on the island for a few decades, following the disappearance of bald eagles due to pesticide poisoning. The presence of nesting golden eagles was indicative of a larger problem: an ecosystem out of balance. Feral pigs, originally introduced during the ranching era (the mid-1800s to late 1970s) had become abundant on the island, and were already known for their devastating effects on the native vegetation. Ignored by bald eagles which feed heavily on fish, the pigs were the perfect meal for golden eagles which hunt land animals.

As golden eagles began nesting on the islands and their numbers increased, they also began hunting island foxes. At only four pounds, the foxes are the largest native land animals on the islands and play vital roles in the plant and animal communities, such as dispersing seeds of shrubs that are unique to the islands. common on the islands but never found on the mainland. They were likely introduced to the islands by Native Americans thousand years ago and played an important role in those societies, as evidenced by the ritual fox burials discovered throughout the Channel Islands.

Island foxes proved to be easy prey because they evolved without predators and don’t have the instinct to hide from eagles. Within a few years on Santa Cruz Island, the fox population dropped from an estimated 2000 individuals to less than 100. Just 15 foxes remained on each of two neighboring islands. The situation needed to be addressed. In 2004, the island fox was added to the endangered species list and Conservancy was engaged in multi-partner and multi-disciplinary efforts to restore the island ecosystem and recover the fox.

Applying our Science

To bring the island fox back from the brink of extinction, the Conservancy and partners launched a multifaceted research, wildlife management, and monitoring program.  Once the research identified the causes of the fox’s decline, land managers translocated the golden eagles directly threatening the foxes and removed their primary food source by eradicating the feral pigs. Scientists designed and conducted a complex pig eradication utilizing GPS technology to track the hunter’s movements. Important new scientific methods around measuring eradication success and confirming completion were developed on the islands in these years. 

At the same time, Conservancy scientists, working closely with statistical experts, designed a dynamic monitoring program. The design allowed the team to adjust the management strategy in response to changes in population estimates or survival rates detected in data from telemetry collars and live trapping. Simultaneously, the Conservancy began a vaccination program to protect the fox from the most dangerous and common diseases that could be accidently brought from the mainland.Also during this time, the Conservancy brought Santa Cruz Island’s foxes into captivity to protect them and to breed them for later release back into the wild once the threats were controlled. 

Meanwhile, Conservancy scientists worked with university researchers, and state and federal agency scientists to develop clear criteria for determining when the island fox would be biologically recovered and thus could be removed from the endangered species list. These criteria were incorporated into the official Recovery Plan written by the Fish and Wildlife Service for the island fox. Data gathered by the island fox monitoring program on fox survival and abundance was used to model the fox’s probability of extinction over the coming 50 years. When that extinction probability remained below a threshold defined by the criteria the recovery team was able to conclude that the fox population was recovered.

Since then, the use of these biologically-based recovery plans for threatened and endangered species have multiplied. For example, criteria based on those developed for the island fox are now being used for the Laysan Albatross and the California Condor.

Nature Conservancy scientist Christina Boser performs a health and identification check on an island fox as part of the field work used collect data and estimate fox abundance through time on Santa Cruz Island.  Photo: © Nancy Crowley

In August of 2016, the island foxes were removed from the endangered species list in the fastest mammal recovery ever accomplished.

Following the removal of the pigs and golden eagles, the foxes were released back to the wild on Santa Cruz Island and  have since flourished. Our monitoring continued and confirmed that the foxes were on their way to recovery.  In 2016, the data indicated that there were an estimated 2000 foxes on the island and in August of 2016 the foxes were removed from the endangered species list in the fastest mammal recovery ever accomplished.


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2016 | Terrestrial | Science | Publications & Reports

Adaptive divergence despite strong genetic drift: genomic analysis of the evolutionary mechanisms causing genetic differentiation in the island fox

Funk, W.C., R.E. Lovich, P.A. Hohenlohe, C.A. Hofman, S.A. Morrison, T.S. Sillett, C.K. Ghalambor, J.E. Maldonado, T.C. Rick, M.D. Day, T.J. Coonan, K.R. Crooks, A. Dillon, D.K. Garcelon, J.L. King, L.M. Lyren, E.E. Boydston, N. Gould , W.F. Andelt

The genomics revolution provides powerful tools for understanding evolution and advancing conservation. This study applies genomics techniques to examine the evolutionary mechanisms underpinning differences in the six populations of island fox on the California Channel Islands. Such insights can be critical for conservation management of…

2009 | Terrestrial | Science | Publications & Reports

Incorporating ecological drivers and uncertainty into a demographic population viability analysis for the island fox

Victoria J. Bakker, Daniel F. Doak, Gary W. Roemer, David K. Garcelon, Timothy J. Coonan, Scott A. Morrison, Colleen Lynch, Katherine Ralls, Rebecca Shaw

Population models can be a critical tool in managing recovery of endangered species. This paper presents an analysis that became the foundation of recovery planning and tracking for the endangered island fox. By combining data from research and long-term monitoring efforts across the six islands…

2015 | Terrestrial | Science | Publications & Reports

Mitochondrial genomes suggest rapid evolution of dwarf California Channel Islands foxes (Urocyon littoralis)

Hofman, C.A., T. C. Rick, M. T. R. Hawkins, W. C. Funk, K. Ralls, C. L. Boser, P. W. Collins, T. J. Coonan, J. L. King, S.A. Morrison, S. D. Newsome, T. S. Sillett, R. C. Fleischer, J. E. Maldonado

Genomics techniques provide powerful means of understanding evolutionary history. This paper examines the evolution of the island fox, which occurs on six of the California Channel Islands. Insights from the research include the role humans played in the evolution of the species, and the remarkably…

2014 | Terrestrial | Science | Publications & Reports

On the fast track to recovery: island foxes on the northern Channel Islands

TJ Coonan, V Bakker, B Hudgens, CL Boser, DK Garcelon, SA Morrison

The island fox is a rare carnivore existing on only six California Channel Islands. In the late 1990’s, due to new and excessive golden eagle predation, it was threatened with extinction on the three northern islands. After extensive and carefully-managed conservation efforts spearheaded by the Conservancy…

2007 | Terrestrial | Science | Publications & Reports

Facing the dilemma at eradication’s end: uncertainty of absence and the Lazarus effect

Scott A. Morrison, Norman Macdonald, Kelvin Walker, Lynn Lozier, M Rebecca Shaw

One of the greatest challenges in pest eradication is knowing when it has been achieved. This paper discusses why that is challenging, and why it is so important to consider how that challenge will be met before any eradication effort is initiated. For many vertebrates,…

2008 | Terrestrial | Science | Publications & Reports

Quantifying eradication success: the removal of feral pigs from Santa Cruz Island, California

DSL Ramsey, J Parkes, SA Morrison

Populations at very low abundance can be very difficult to detect. Consequently, one of the biggest challenges of eradication projects is determining whether an inability to detect the species at the presumed end of a project means that it has been completely removed. A helpful…

2010 | Terrestrial | Science | Publications & Reports

Rapid eradication of feral pigs (Sus scrofa) from Santa Cruz Island, California

John P. Parkes, David S.L.Ramsey, Norman Macdonald, Kelvin Walker, Sean McKnight, Brian S.Cohen, Scott A. Morrison

This paper describes the approach, planning, and field implementation of an intensive effort to eradicate a population of feral pigs from an island. Key elements of the project included comprehensive data collection of all field effort and outcomes, and comprehensive use of helicopters in nearly…

2007 | Terrestrial | Science | Publications & Reports

Reducing risk and enhancing efficiency in non-native vertebrate removal efforts on islands: a 25 year multi-taxa retrospective from Santa Cruz Island, CA

Scott A. Morrison

Eradication of invasive non-native species is often necessary to protect island ecosystems. Eradication efforts can nonetheless be risky investments. How they are planned and implemented can greatly reduce the risk of failure. Santa Cruz Island provides an interesting case study in eradication, because a variety…