New Technology for Monitoring Island Foxes

Monitoring island fox survival is vital to protecting the vulnerable and small populations on six separate Channel Islands. (Current island fox status)

 

Checking for the individual radio signals from 50–60 individual island foxes across an entire island every two weeks, can require many staff hours. Reducing staffing hours would make island-fox monitoring less expensive?

Enter a new technology referred to as "Digipeater." The collar pictured above is one of the 10 new Digipeater radio collars funded by FIF and fitted on Santa Cruz Island foxes this summer. While the collar size is similar to VHF radio-tracking collars, the new collars weigh slightly less and have an additional ability: they interact with stationary digital repeating antennae in the field. 

Multiple times a day, receivers on the antenna scan for fox-collar signals. When a signal is picked up, it's relayed from one antennae to another until it reaches a base station. The base station transmits information directly to biologists. A biologist doesn't have to be in the field to know that all collared island foxes are active and well.

If an island fox goes for a number of days without being picked up by the automated system, biologists can go into the field looking for the signal from that specific fox.

 

The U.S. Navy on San Clement Island has been using Digipeaters for several years. Last summer during a wildfire that burned across a third of the island, biologists were restricted from going into the field. As the low-burning wildfire spread, the Digipeaters continued to collect status information on island foxes. From a safe location biologists could detect island fox activity and survival. No collared island foxes died in the wildfire. 

 

This Santa Cruz Island fox was fitted with a "Digipeater" collar in July. Her new collar reports in daily and requires less in-person labor. It's a win-win for monitoring island foxes.

These collars are possible, because of donors like you. 

Digipeater collars are $350 each and are made locally in Southern California. 

Island Fox Status Update 2025

In 2024, island foxes remained healthy. Normal rainfall levels led to population balancing; high density populations decreased in number and low density populations increased. San Clemente Island, however, realized a third consecutive year of population decline. Concern for these island foxes grows because a specific cause for the decline remains unknown.

island fox on San Clemente Island

The following is an update across the Channel Islands from notes compiled by Friends of the Island Fox at the Island Fox Conservation Working Group Meeting May 15, 2025 hosted at the Santa Barbara Zoo (hybrid meeting).

Reported population numbers are the official estimates submitted by the land managers and calculated by them from island foxes captured for health checks June 2024–January 2025. (How island foxes are captured and given health checks) 

Overview: While food and shelter resources for island foxes were good across the islands in 2024, dry conditions were more prevalent on San Clemente Island and a wildfire burned a third of the island. Monitoring systems documented island foxes surviving the fire, but it is possible the fire contributed to the low number of pups documented. Weather extremes are becoming more frequent across the islands. 

Fox Density: Because island size, weather, and habitat varies from island to island, comparing island fox density can be more informative than comparing population sizes. Fox density reflects the number of island foxes found within a square kilometer (per sq km). (More on density).

A density of 8–12 island foxes per sq km, is the fairly high density of individual animals typically found across the Channel Islands. When a density rises above this range, as San Miguel Island did in 2023 (see graphic above), it is not surprising when the population adjusts down the following year, especially if weather conditions are not optimum for growing native fruit and supplying large amounts of insect and rodent prey.

The two smallest islands with island foxes, San Miguel and San Nicolas, remain most stable when their population density is around 8 island foxes per sq km. Food resources on these smaller islands are never as plentiful as on the larger islands. While the population number decline on San Miguel may seem concerning, the downward adjustment in density creates a more sustainable population. 

The larger islands, Santa Rosa, Santa Catalina, and Santa Cruz provide greater biodiversity of resources and can maintain higher island fox population densities. Densities over 12 foxes per sq km, however, can mean that some island foxes are pushed to very small territories with lower quality resources. Drought, flooding, or the introduction of disease, often has a greater negative impact when foxes are living in high density.

The density graphic above also shows how thin the island fox density was on San Clemente Island in 2023 and 2024. Everyone is watching this island closely and investigating leads on the causes. 

Pup on Northern Islands in August 2024

 

In 2025, the leading threats to island foxes are:

• reduced funding for Federal lands: Monitoring island foxes requires staffing. Reductions in Federal funding for National Park staffing, especially biologists, and unknown budgetary cuts affecting U.S. Navy base environmental efforts threatens island fox health checks and monitoring in 2025. Across Federal lands health checks began early in hopes of completing them before funding cuts were enacted. The ability to continue monitoring on Santa Rosa, San Miguel, San Clemente, and San Nicolas Islands remains in jeopardy for 2026 and into the future. 
• biosecurity: Annual vaccination of island foxes for the deadly canine distemper virus remains a priority. If health checks are discontinued on Federal lands, there will be no annual opportunity for vaccination. Additionally, canine adenovirus (dog flu) has swept across several islands and may be impacting pup survival.
• climate change: Weather extremes not only influence island fox health and resources, they also impact island fox monitoring. The heavy rains of 2023 limited access to Santa Cruz Island and the data collected that year led to a false representation of an upward spike in population numbers. Quality monitoring requires consistency in data collection. Monitoring data in 2024 revealed a stable population on Santa Cruz–mitigating the spike. This highlights the importance of annually collected data to provide the most accurate depiction of island fox population trends across the islands.    

island fox having teeth examined during a health check

 

Greatest Concern: We know how quickly an entire population of island foxes can be impacted by disease, resource loss, or an introduced threat. Quality monitoring is the cornerstone of island fox recovery success. Millions of dollars invested in island fox recovery could be swept away to save a few $100,000 in annual monitoring costs. 

 

Smaller Islands

Because of the amount of years tracked, the graph above shows population estimates for even years only. While smaller populations can be more volatile, San Nicolas and San Miguel Islands remain stable. 

San Miguel Island (lime green line): The downward adjustment of the population from an estimated 525 individual island foxes to 322 reflects a rebalancing to a more sustainable population density. Trends suggest the resources on the island can support 300–450 foxes. Pup numbers were typical in 2024 and individual health appeared good.

San Nicolas Island (pink line): The population remained stable. General health remained good and pup numbers increased. Forty percent of the population shows antibodies for exposure to adenovirus. Ear mites are prevalent. In 2025 foxes receiving health checks will be treated with a topical intervention, following protocols developed on Catalina Island. The hope is to reduce ear mite infestation and increase overall health.

San Clemente Island (blue line): Adult survival dropped from an 89% chance of surviving the year to 69%, and only 7 pups were documented in 2024. Investigations continue into pup survival, the impacts of adenovirus (exposure now prevalent in 80% of the population), and the quality of food resources. The wildfire may have also contributed to population decline. Car strikes add an additional threat to survival. Providing necropsies of individuals killed by vehicles may be vital to identifying health concerns that have gone undetected. 

Larger Islands

Because of the amount of years tracked, the graph above shows population estimates for even years only. As all of these islands hover at carrying capacity, their populations remain stable.

Santa Catalina Island (red line): This population increased slightly in 2024. Treating island foxes for ear mites has reduced cancerous tumors and increased overall health. Introduced adenovirus, corona, herpes, and parvo viruses all continue to decline. Biosecurity threats are greatest to this island, but no raccoons or other invasive species were detected on the island in 2024. The greatest threats to island foxes on this island are people and their pets. Eighteen island foxes were killed by cars and two were attacked by dogs. Rodenticide and unintended poisoning is a growing threat on all human-inhabited islands.

Santa Rosa Island (pink line with black centers): This island currently has the greatest island fox density–13.2 island foxes per sq km. As the density has increased, adult annual survival has declined slightly to a 72% chance of surviving the year. How this high density impacts available resources and fox territory is under investigation this summer with a group of known individual foxes wearing GPS tracking collars and being monitored for diet and health.

Santa Cruz Island (black line): This island continues to have the largest island fox population. As expected, the estimate of over 4,000 individuals in 2023 was an anomaly created by not being able to count foxes at historic counting locations because of stormy weather and flooding. Returning to count in the historic spots in 2024 resulted in a scientifically supportable and healthy population estimate of 3,086. 

Your donations help fund vaccinations and radio collars for monitoring island foxes. 

As July and August unfold, biologists are in the field vaccinating island foxes and fitting them with radio-tracking collars funded by Friends of the Island Fox.

Healthy island foxes depend on people like you supporting conservation efforts. 

 

Vaccinating Island Foxes Takes a Community

 $15,322 of vaccine is headed into the field to protect island foxes!

Donors like you made this possible! 

courtesy M. Navarro, NPS

Why do island foxes need to be vaccinated annually?

Canine distemper virus (CDV) caused a catastrophic decline of Santa Catalina Island foxes 26 years ago. Evolving in isolation on their islands, island foxes haven't developed immunity to typical canine diseases. To protect populations, each year at least 100 island foxes are vaccinated on each island against this deadly dog disease and rabies. On Catalina the goal is to vaccinate 350 island foxes, because the threat of introduced disease is so much higher for this population.

Island foxes are so susceptible to CDV that they can not tolerate the vaccine commonly given to dogs. They must be vaccinated with a special dead-virus vaccine that is produced in small batches and only provides protection for less than a year.

That means island foxes need to be vaccinated annually and the effort is one of the more expensive measures taken to protect their health each year.

This year's 650 vaccinations were supported by:

• Island Fox Ambassador Schools & Projects
• Local organizations 
• Recycling 4 Island Foxes & the Planet
• USU Recycles 4 Island Foxes
• 2024 FIF Island Trip participants 
• Private donors
• a grant from the Fresno Chaffee Zoo Wildlife Conservation Fund

How do you vaccinate an island fox? 

Metabarcoding Reveals the Genetic Fingerprints of Prey in Scat

 

Scat samples from island spotted skunks and island foxes were collected last December on Santa Cruz Island. The samples were part of a trial research project to determine if a conservation working dog, Moose, could accurately locate and identify island spotted skunk scat. Meet Moose; How accurate was Moose?

A total of 15 island spotted skunk scats were compared to island fox scats using metabarcoding. 

Metabarcoding is a process that takes a general biological sample and sifts out short sections of DNA and matches them to known strands of DNA representing different species. Using this process, a sample of pond water can provide a list of species that have been in that pond. In the Florida Everglades biologists are using metabarcoding to locate invasive pythons. The pythons shed DNA into the environment and metabarcoding can identify their presence.

 

In a scat sample, metabarcoding can help identify food items that an animal has eaten, especially when that prey may not leave exoskeletons, seeds, fur, or bones visible in the scat. (Scat & fox diet)

If island foxes and island spotted skunks are competing for the same food resources, the growing number of island foxes could have a population-limiting impact on the smaller species, the island spotted skunks. (Island foxes and island spotted skunks)

The preliminary results are very interesting.

There was an overlap in some prey species. Both island foxes and island spotted skunks were consistently consuming Jerusalem crickets in the fall of 2024. This large insect is an important food resource for both species. 

Jerusalem cricket

Deer mice appeared to be more important in the diets of island foxes than island spotted skunks. Both species also preyed on katydids, millipedes, and crane fly (most likely the larva which can be large and pump in the fall). For these three arthropods, island foxes were more likely to include them in their diet than island spotted skunks.

 

There were also a large number of prey items that were unique to either foxes or skunks.

Island foxes were frequently eating ground beetles and earwigs, which skunks were not eating. They were eating faster-moving diurnal species like: grasshoppers, song birds and quail. They were consuming fly and moth species that were different from those consumed by the skunks. Island foxes were also occasionally consuming snails. While snails might seem a slow-moving, nocturnal prey, their DNA did not show up in the skunk scat. 

Island spotted skunks were also consuming unique prey species. Several moth species were detected and more than a third of skunk scats revealed moth DNA. Island spotted skunks are strictly nocturnal and it's not a surprise that nocturnal species like moths and field crickets would be prey. Surprisingly, petrel DNA, a sea bird, was also found in about a third of the scats. These are small marine birds nesting in sea caves on the islands. Slender salamanders, a small terrestrial species most likely found in moist canyon soils were a common food source, while weevils and butterflies (possibly overwintering chrysalis) were occasionally eaten.  

While this was a preliminary study over a short amount of time with a small sample size, it suggests that, at least in the fall, there is not a lot of overlap in resource use between island foxes and island spotted skunks. We don’t know how many different island foxes or island spotted skunks are represented by the scat samples and more data is definitely needed.

The scat samples are currently being evaluated for plant DNA.

A Nose for Identifying a Species

Last December, Friends of the Island Fox worked with The Nature Conservancy and Working Dogs 4 Conservation on a project to see if a specially trained dog could track down island spotted skunk dens and scat. (See Moose the conservation working dog)

courtesy of TNC and WD4C

 

In the initial project, Moose used his specially trained nose to locate 11 scat samples. Two scat samples were also found by humans. The samples were sent to the Genetics Lab at UC Davis and Friends of the Island Fox helped fund the genetic testing of the samples. How well did Moose do identifying island spotted skunk scat from island fox scat?

Moose: 9 out of the 11 scats came from island spotted skunks. 1 sample was too degraded for DNA analysis (it might have been skunk) and 1 sample was island fox scat. 90% accurate!

Humans: 1 of the 2 scats came from an island spotted skunk, the other was island fox. 50% accurate!

 

Obviously, Moose is better than humans at detecting island spotted skunk scat.

island fox scat

The next questions: 

• Is there enough quality DNA in a scat sample to determine the identity of an individual island spotted skunk?
• It would cost $7,000 to develop island spotted skunk genetic markers to determine individuals. Can enough scat be located to establish a population estimate and would it be fiscally feasible to count the population this way?

 

The other information obtained from the scat samples pertains to diet. Island spotted skunk scat was compared with island fox scat. Stay tuned for more on metabarcoding.

Why do we need to count island spotted skunks?

Fox Foto Friday - Creating a Living Library

 What's in these vials?

 

courtesy L. Brenner, TNC

Island fox blood samples going back decades. 

During annual health check-ups, samples are taken of island fox blood. Blood samples can be used to screen for increased antibodies to a specific virus, to check for toxins, or to provide genetic information.

 

 

These island fox blood samples from Santa Cruz Island are currently being archived and prepared for long-term cryogenic storage at the Museum of Southwestern Biology (MSB) at the University of New Mexico. 

For years, island fox samples have been housed in freezers spread across counties and agencies. While a collection of samples are stored at the School of Veterinary Medicine at UC Davis, samples from different islands have been stashed in a variety of locations with ever-changing safety measures or lack there of. The value of these specimens to science is degraded if they experience unreliable freezing, are not accessible, or are misplaced.

In 2023, FIF worked with the Dept. of Defense and the U.S. Navy to move some specimens from San Nicolas Island foxes to the Museum of Southwestern Biology (MSB), one of the largest and most advanced centers for archiving mammal specimens.

 

At the end of 2024, FIF assisted The Nature Conservancy with sending historic island fox blood samples from Santa Cruz Island to the MSB. The last group arrived in New Mexico March 26, 2025.

FIF's goal is to have scientific samples from all six islands archived, protected, and available to future researchers. 

 

Island foxes on San Miguel and Santa Rosa Islands have been through a historic genetic bottleneck; one that most geneticists considered impossible to recover from. Yet today, island foxes persevere. Island foxes can teach us about evolution, adaptation, and species sustainability. The information in this living library will provide future researchers with access to crucial data.

Donations to FIF help support important island fox research 

Apply for FIF's 2025 Research Grant 

Genetic research currently supported by Friends of the Island Fox:

• Transcriptomics in RNA and island fox health
• Comparing the genetics of the small founding populations on San Miguel and Santa Rosa Islands with today's island fox populations

Friends of the Island Fox Research Grant 2025

Friends of the Island Fox 

is currently accepting applications through June 15 

for the FIF 2025 Research Grant

 

Download Grant Application

In 2025, Friends of the Island Fox is offering up to $7,000 in support to research projects benefiting greater understanding of the island fox and the Channel Island ecosystem.

From the genetic impacts of near extinction and specific genetic influences on health to drought impacts on fox diet and counting island spotted skunks, FIF supports research to improve the understanding of island fox survival and the complexity of the Channel Island ecosystem.

See prior grant winning projects.

It's all Science for Fox Sake!

 

Scientific data is vital for making informed conservation decisions. Your donations help gather scientific knowledge and build the next generation of scientists and field biologists. 

"Date with a Fox" - Investigating Causes of Death in Island Foxes

Join Friends of the Island Fox for an insightful look into island fox health with veterinary pathologist, Leslie Woods, Ph.D. 

"Date with a Fox" Zoom Program

Mortalities in the Channel Island Fox 

(Urocyon littoralis)

The important role of postmortem examinations

Tuesday, March 18 at 6:30 pm PT

 

Leslie Woods, Professor Emerita of the California Animal Health and Food Safety Laboratory at the School of Veterinary Medicine at U.C. Davis has been investing island fox health since 2010.

Though retired, she continues to teach and performs all of the necropsies on island foxes.

What are the current health threats to island foxes? Why is it important to evaluate cause of death for wild animals? Professor Woods is a wonderful teacher and a true detective. 

Watch Recorded Video Program

(Be advised this program contains images of dead island foxes and bodily organs. Examination to determine cause of death is important, but the subject may not appeal to all viewers.)

Professor Wood's work provides factual scientific evidence so land managers can make informed decisions to help keep island fox populations healthy and safe.

 

FIF Supports Research into the Impact of a Genetic Bottleneck on Island Foxes

When a population declines to a small number of survivors and then increases dramatically over the next few generations, there are always questions about genetic issues.

Meet Elisabeth Leung a student at the University of California at Riverside. Working with her advisor Professor Ellie Armstrong, Leung is “Exploring founder contributions from the captive island fox breeding programs for Santa Rosa and San Miguel Island using genomic sequencing.”

FIF is supporting Leung’s research because she is delving into an important question with long-lasting consequences for island foxes.

 

Around 26 years ago, the island fox populations on Santa Rosa and San Miguel Islands dropped to a critically low number: 15 surviving individuals on each island. When we look at Santa Rosa’s estimated population of 2,536 island foxes in 2023, all of them have descend from just 12 individuals in captive breeding: 4 males and 8 females.

Elisabeth Leung’s investigation will look directly at the genetics of the original founding individuals on Santa Rosa Island and San Miguel Island and compare their DNA to their descendants on the islands today.

 

Why is this important? Typically a population has some members with genetic-related health issues, maybe a tendency toward heart problems, a physical deformity, or an increased occurrence of specific cancers. Usually, these individuals are a small minority in the population because they are less successful passing on their genes before they die. When survivors are randomly chosen, rather than because they have traits that drive their success, traits that are not necessarily beneficial can increase across a population; this is called “genetic drift.”

With just 4 males contributing to the first generation of captive-born island foxes on Santa Rosa Island, if just one of those males carried a gene that increased health risks, a greater percentage of the population could be impacted. The recovered population might then have higher numbers of individuals with non-beneficial genetic traits. Overtime this would be expected to cause “inbreeding depression”–a magnification of negative traits and reduction in species vigor.

The Florida panther (Puma councilor coryi) is a well-known example of “inbreeding depression.” Genetic problems arose as the population became very small, leading to reduced male fertility and noticeably kinked tails. The inflammation response of Santa Catalina Island foxes to ear mite infestation may be linked to genetics or epigenetics and is currently being investigated by Alexandria DeCandia at the Smithsonian.

biologist examines island fox ear during health check

Though geneticists have raised concerns about island foxes, there is no evidence of current genetic problems.

Today genetic research can delve deeper into DNA and health-related issues than it could 26 years ago. See FIF Grant for Transcriptomic Research

Leung’s research will help us understand the evolutionary impact of recovering from a small founding population. Has there been genetic drift in the fox populations on these two islands? What has changed or not changed in island fox genes?

To examine these changes, the lab at UC Riverside is also creating the first island fox reference genome. The island fox pictured here is fox “25205” on Santa Rosa Island. Blood samples from this island fox will be used to assemble the first complete island fox genome.

Genetic research has entered a golden age and donors like you are helping uncover important genetic information to help island foxes survive into the future.

Conservation Working Dogs and Zoos Helping Wildlife

photo courtesy of TNC and WD4C

 

Meet “Moose” a hard-working canine with the nonprofit organization Working Dogs for Conservation (WD4C).

Moose recently completed a tour of duty on Santa Cruz Island as part of a multi-organizational effort to find a better way to gather information on island spotted skunks.

Island spotted skunks only live on Santa Rosa and Santa Cruz Islands. As island foxes recovered on these islands, island spotted skunks seemed to have declined. There is concern for these rare little skunks and a lack of understanding about their relationship with island foxes. Do island foxes directly impact island spotted skunks? Do they compete for similar resources?

Friends of the Island Fox has supported several research investigations into this relationship:

• C. Gagorik and V Zhang: "Examining habitat use and movement patterns of island foxes and island spotted skunks on Santa Cruz Island”
• J. Schammel: Dietary overlap and change between island foxes and island spotted skunks on Santa Rosa Island
• J. Owen: Genetic relationships of spotted skunk subspecies
• D. Thomaier: Occupancy modeling of island spotted skunks on Santa Rosa and Santa Cruz Islands using field cameras 

In 2024, the question arose about western spotted skunks in captivity that might participate in research studies as a control for island spotted skunks. FIF’s Education Director, Keri Dearborn, did an internet search and found “Boo” a female western spotted skunk at the Sequoia Park Zoo. Boo and her two brothers had been orphaned when they were very young. Though they were rescued, they became imprinted on humans and couldn’t be returned to the wild. Boo was living at the Sequoia Park Zoo in Eureka and her two brothers were at the Turtle Bay Exploration Park near Redding.

 

While Thomaier’s field cameras have documented island spotted skunks, to-date identifying individual skunks in images has been very difficult. Island spotted skunks push off radio collars and typically avoid capture.

Lara Brenner, Island Scientist with The Nature Conservancy, had been working with a conservation dog to sniff out invasive Argentine ant colonies on Santa Cruz Island. Could a conservation working dog locate island spotted skunk dens? Finding scat and dens would be less invasive than capturing skunks and might open up a whole new way to determine their numbers.

Moose gets suited up for work

 

Moose had experience tracking grizzly bears and locating their dens. Could he do the same job for tiny island spotted skunks? Protocol for a test was put in place. Because island foxes are susceptible to canine diseases and because island foxes can be a source of disease for dogs, Moose was up-to-date on all of his vaccinations.

The two zoos collected soiled bedding and feces from the three western spotted skunks. The fragrant material was sent to a WD4C training location in Montana, where Moose learned to identify spotted skunk scent. Would the western spotted skunk scent be close enough to the island spotted skunk scent for Moose to be successful?

 

Toward the end of 2024, Moose and his handler traveled to Santa Cruz Island. Moose “hit the ground running,” Brenner says. As a conservation working dog, he wears a special harness with bells and a GPS locator. Brenner explains that the GPS locator “is so that we can record his tracks and understand [his] search effort… i.e. how far does Moose have to go and how long does he have to sniff before he finds a skunk?”

On the first day, Moose signaled his handler that he’d found an island spotted skunk den. 

Working the hillsides with a canine nose, detection dogs are more efficient than people and have a higher success rate locating a target species. Over three weeks, Moose found several den sites, including this one with an island spotted skunk at home, and 12 scats.

Island spotted skunk in den (courtesy of TNC)

Can DNA from the scats identify individual island spotted skunks? Can genetic meta-barcoding of scat samples identify specific dietary items for island spotted skunks and island foxes? We’re just at the tip of learning how working dogs like Moose can contribute to island conservation?

courtesy of TNC and WD4C

 

This project is a multi-institutional collaboration between Sequoia Park Zoo, Turtle Bay Exploration Park, The Nature Conservancy, Working Dogs for Conservation, and Friends of the Island Fox. The biggest credit goes to the four-footed collaborators: the three western spotted skunks who are helping their wild counterparts and a very talented working dog named Moose.